1.7 rocker effect

[converted1]

I'm considering adding a set of 1.7 rockers to my build, intake only,its a tman 590 cam, how does the additional lift figure in.
1 will it help make more hp\ if so to the left or right
2 will it help make more torque/if so left or right

[Admiral Akbar]

They will gain about 2-3 degrees of 0.053 equivelent duration and add lift.. Overall you motor can breath a little better.. Typically it increase peak TQ and HP but not do much on the low end unless head flow is limiting..

[HD/Wrench]

OR it will do nothing at all , ( other than lighten your wallet)  Tested that been there and got the tee shirt.. With testing it on your set up there is no way to know and testing means getting the bike on the drum that day up to temp make the base line, pull it down swap the rockers then re tune and test.. At least that is how we did it on a a few different cams. Even easier if you have two extra supports ready to go . Look forward to the results 

[Admiral Akbar]

OR it will do nothing at all , ( other than lighten your wallet)  Tested that been there and got the tee shirt.. With testing it on your set up there is no way to know and testing means getting the bike on the drum that day up to temp make the base line, pull it down swap the rockers then re tune and test.. At least that is how we did it on a a few different cams. Even easier if you have two extra supports ready to go . Look forward to the results 

Absolutely.. At least you got the T shirt... 

[sfmichael]

best results I've seen are where the cam is too small to begin with, not likely with the TMan 590...and as Max stated if the heads are lame the additional lift will help

not knowing what you have for heads is a bit of a wild card - but I'd guess 1-3 hp/tq
I personally have never seen really big gains but can be worthwhile on some builds

Steve/GMR nailed it with his comment 

[HD/Wrench]

OR it will do nothing at all , ( other than lighten your wallet)  Tested that been there and got the tee shirt.. With testing it on your set up there is no way to know and testing means getting the bike on the drum that day up to temp make the base line, pull it down swap the rockers then re tune and test.. At least that is how we did it on a a few different cams. Even easier if you have two extra supports ready to go . Look forward to the results 

Absolutely.. At least you got the T shirt... 

Yep it says " max went to AZ and all I got was this stupid shirt"   HA HA

[pwmorris]

Gain, achieve nothing at all, or lose power. Depending on cam, compression, heads, pipe etc, I have lost torque going to the higher rocker ratio...
As said, gotta test and find out if your combo likes it-or not.
If you can't, don't want to, or don't have access to repeated straight swap, no other changes dyno testing, leave it as is with stock ratio. Some like stock, some like intake only, and some motors like intake and exhaust...

[Matt C]

If the heads are "lame" it won't help at all because "lame heads" won't flow any more
at higher lifts. And the added duration is so negligible, I doubt you'd even be able to
notice it on a dyno. The margin of error is probably greater than any gains you would
get.

Save your money, that's a good cam you have in there.

[NHBagger]

There may be better ways to make more HP or TQ, depending on what you want.  What's the rest of your setup?

[converted1]

107 ci set at 10.8 (est) ccp 205 (est)
massaged on MVA'S
massaged on SE 58MM T/B---5.3 inj
TMAN 590 CAM
RUSH WRATH 2.50

[Admiral Akbar]

 

So what are you trying to accomplish?

[sfmichael]

If the heads are "lame" it won't help at all because "lame heads" won't flow any more
at higher lifts. And the added duration is so negligible, I doubt you'd even be able to
notice it on a dyno. The margin of error is probably greater than any gains you would
get.

Save your money, that's a good cam you have in there.

I know you know it all but I have seen decent gains with stock heads. The valve will be open farther at low/all lifts than it would be normally with stock ratio rockers. They don't only open the valve farther at maximum lift...where the headflow typically flatlines in relation to lift.

[Barrett]

They worked well with my 37's.

[Don D]

I thought TW37s had .510 lift with stock rocker ratio?
This can't be a graph of 37s right?

[BVHOG]

TDC lift and valve to valve clearance will be horrendous with a 590 and high ratio rockers.

[sfmichael]

I thought TW37s had .510 lift with stock rocker ratio?
This can't be a graph of 37s right?

correct

[Matt C]

TDC lift and valve to valve clearance will be horrendous with a 590 and high ratio rockers.

Don't confuse them with facts...

[converted1]

I just happen to have a set lying around,and have seen them added to builds,and was hoping I could use them to get a little more
So I threw the question out here to get the pro's and cons,in this case looks like the cons rule the roost

[Matt C]

I know you know it all but I have seen decent gains with stock heads.

prove it

[Raleigh111]

i do not know the answer to what i am about to say so dont take this the wrong way, asking not stating or telling.

a while back i had a conversation with a guy that makes cams for a living and he said dont bother with those high ratio rocker arms it will rob you of horsepower as it takes more force to lift them. if you want higher lift buy a different cam, gave me some example of a tidder todder at a park? still trying to figure that out in my head. car guys use them all the time and have been for many many years.

i used them anyways and it helped me in my situation?

[Barrett]

I thought TW37s had .510 lift with stock rocker ratio?
This can't be a graph of 37s right?

The graph is from a car guy.. His name is on it.
The TDC would come in at .222

[Barrett]

Here's a test from a car site.. Lifting the valve more than the heads flow didn't make any gains. It did help up to that point.
http://www.hotrod.com/how-to/engine/116-0101-roller-rocker-ratio-test/

[Matt C]

If you need to use high ratio rockers, you have the wrong cam.

[No Cents]

   just curious here...but why did S&S design their new T143 crate engine and use 1.725 rockers arms in that engine?
It seems if the 1.725's didn't help...they would have ran the stock ratio arms.

Ray

[aswracing]

I've carefully tested them multiple times, in various engines, where the change in rocker ratio was the only change I made. I've seen between zero and 2hp improvement, depending on the application.

The rocker arm geometry is a key part of the equation. If it's not right, you may not get even get any measurable additional lift out of them. They're really not a bolt-on mod.

[Raleigh111]

   just curious here...but why did S&S design their new T143 crate engine and use 1.725 rockers arms in that engine?
It seems if the 1.725's didn't help...they would have ran the stock ratio arms.

Ray
i do not know the answer to what i am about to say so dont take this the wrong way, asking not stating or telling.

a while back i had a conversation with a guy that makes cams for a living and he said dont bother with those high ratio rocker arms it will rob you of horsepower as it takes more force to lift them. if you want higher lift buy a different cam, gave me some example of a tidder todder at a park? still trying to figure that out in my head. car guys use them all the time and have been for many many years.

i used them anyways and it helped me in my situation?

i thought that exact same thing when i saw they were using them!! if they rob horsepower why not have rocker arms with even lower ratio ? geometry ?

[pwmorris]

Here is some notes from Jim Hand, a Pontiac car guy, but the testing results were similar to mine.
Harley street motors with very moderate lift and compression don't exactly tax a valve train, but I have seen Jesel rockers in a VTwin with a 1.9 intake rocker ratio, so used wisely in the right motor combo, adding lift in either the intake or both rockers can see benifits-Including my current 126" street bike motor running 1.7's on just the intake (didn't test using both int and ex, as I was happy with the results as is, but maybe in the future).

JH-
" If the 1.5 arms are replaced by 1.65. Is this good? On any engine that can use the extended duration, it is very good. A 455 with the 068 will feel much stronger in the normal driving range and will pick up as much as .2 seconds in the 1/2 with this change. However, if the cam duration is already adequate with 1.5 ratio arms, the added duration caused by 1.65 arms may result in a loss of performance. We recently witnessed a 455 street car that runs in the 12.70 range with a 041 cam lose performance and driveability when the stock 1.5 rockers were replaced with a set of 1.65 Harland Sharp units. The 041 cam/1.5 rocker combination exactly matched the overall setup of this vehicle, and the increased cam timing unbalanced the combination.

A change in rocker arm ratio can provide a significant boost in usable power, or they can actually cause a loss, depending on what duration and lift the engine needs and what it has before the change. Note that push rod length and stiffness, and lifter leakage, can affect actual valve lift, but these factors will remain relatively constant. The real concern is not theoretical numbers, but how your engine responds to the overall combination."

[Raleigh111]

Here is some notes from Jim Hand, a Pontiac car guy, but the testing results were similar to mine.
Harley street motors with very moderate lift and compression don't exactly tax a valve train, but I have seen Jesel rockers in a VTwin with a 1.9 intake rocker ratio, so used wisely in the right motor combo, adding lift in either the intake or both rockers can see benifits-Including my current 126" street bike motor running 1.7's on just the intake (didn't test using both int and ex, as I was happy with the results as is, but maybe in the future).

JH-
" If the 1.5 arms are replaced by 1.65. Is this good? On any engine that can use the extended duration, it is very good. A 455 with the 068 will feel much stronger in the normal driving range and will pick up as much as .2 seconds in the 1/2 with this change. However, if the cam duration is already adequate with 1.5 ratio arms, the added duration caused by 1.65 arms may result in a loss of performance. We recently witnessed a 455 street car that runs in the 12.70 range with a 041 cam lose performance and driveability when the stock 1.5 rockers were replaced with a set of 1.65 Harland Sharp units. The 041 cam/1.5 rocker combination exactly matched the overall setup of this vehicle, and the increased cam timing unbalanced the combination.

A change in rocker arm ratio can provide a significant boost in usable power, or they can actually cause a loss, depending on what duration and lift the engine needs and what it has before the change. Note that push rod length and stiffness, and lifter leakage, can affect actual valve lift, but these factors will remain relatively constant. The real concern is not theoretical numbers, but how your engine responds to the overall combination."

good info thanks! Makes sense you use them to fine tune if the cam is one way or another? any mention of it taking more force to lift the higher ratio arm?

[1FSTRK]

You take the valve spring pressure and multiply it time the rocker ratio to get the pressure on the lifter.

The smart guys will account for this when picking cams and setting up springs for the ratio of the rocker.

[Admiral Akbar]

107 ci set at 10.8 (est) ccp 205 (est)
massaged on MVA'S
massaged on SE 58MM T/B---5.3 inj
TMAN 590 CAM
RUSH WRATH 2.50

With this build I would almost best that what Paul (pwmorris) says rings true... No gain maybe some loss..

[1FSTRK]

There have been several that have already posted that experience and testing is the only real way to tell for sure.

Here a good example of "you do not know unless you test".



Care to guess which run is a 590 lift 246 duration cam with stock ratio rockers and which is the .511 lift 242 duration cam with 1.725 ratio rockers. Both were fully tuned.

[Matt C]

Blue line - stock rockers

[1FSTRK]

Blue line - stock rockers

Buzzzzzzzzzzzz

Want to try the bonus round where the prizes are double?


ADDED
MCE, Not trying to be a knob, my attempt at humor, don't take it as a personal jab.

Here is a 105ci Woods 9F with Stock ratio rollers and with 1.7 ratio rollers.
It required bigger thunder jets and less timing.
They do not always work out like this but the test is the only way I have seen anyone know for sure.

[Matt C]

I'm ok with it 

Sometimes it works, sometimes it doesn't. Only one way to know. Right?

[jam65]

If you need to use high ratio rockers, you have the wrong cam.

So what is your position on this subject?

[Matt C]

If you need to use high ratio rockers, you have the wrong cam.

So what is your position on this subject?

I feel these are more of a fine tuning or an R&D tool, (to see if the motor wants more
cam).

I'm not a fan of using them as a permanent solution. Although that certainly has been
done by others. jmo tho

[PanHeadRed]

I'm considering adding a set of 1.7 rockers to my build, intake only,its a tman 590 cam, how does the additional lift figure in.

I'd put them in on both sides, assuming parts won't collide. If only one side I'd consider the EX side as strongly as the IN side as valve movement will speed up and that in it's self is a benefit. But as others have stated sitting on the bench they only offer potential, added to the engine is the only way to determine if your application will realize the potential.

Any part that opens the valves higher and/or faster has the potential to add power.

[Durwood]

If you need to use high ratio rockers, you have the wrong cam.

So what is your position on this subject?

I feel these are more of a fine tuning or an R&D tool, (to see if the motor wants more
cam).

I'm not a fan of using them as a permanent solution. Although that certainly has been
done by others. jmo tho

I agree, I did see some performance gains with them in my 103' with 204's, so I went to AP-57's.

I have seen two different builds with these ran long term, 15k and 25k, that an exhaust lifter took a dump, it actually took the roller needles out.

I can't say for sure that it was the 1.725 rockers that caused the failure but both builds had good quality tappets.

After some research I feel the leverage increase may very well have been the culprit.

Daren

[1FSTRK]

Lets look at the math rather than the myth.

First look at an example of close to stock numbers
Ratio    lifter seat    lifter open  spring seat   spring open
1.625   219.4 lbs   650.0 lbs   135.0 lbs        400.0 lbs

Now with the 1.725
1.725   232.9 lbs   690.0 lbs   135.0 lbs        400.0 lbs

And the increase pressure at the lifter with 1.725 ratio
Increase     13.5 lbs     40.0 lbs

Now say you buy some fancy high performance springs for your stock ratio rockers
Ratio    lifter seat    lifter open  spring seat   spring open
1.625   260.0 lbs   780.0 lbs   160.0 lbs   480.0 lbs

As you can see the spring kits far exceed the the lifter pressure of simply adding the bigger ratio rockers.

Now there are things to consider when using higher ratio rockers with performance springs when you set the spring pressure but any good cylinder head specialist will know this and take care of this when setting things up for you.

Some of the things to consider are the weight of the lifter and pushrod are not accelerated as quickly and do not move as far with the smaller cam and the higher ratio rocker for the same valve travel. Also because the valve spring not only closes the valve but also pushes the pushrod and lifter back down it's job is easier because it now has more leverage over the pushrod and lifter so less spring pressure would be needed to move the same weight. There is a lot more to it but simply put running a stage two cam with higher ratio rockers will not over load your lifters or hurt your longevity unless you really screw up something else in your set up.

[sfmichael]

good stuff 

[Durwood]

As I stated Eric, I am not sure exactly what caused these failures, but they were both hot rods, and both lost the rear exhaust lifter.

The set of SE 1.725 I took off of my bike with about 5k on them both of the exhaust rocker tips had some abnormal wear, one much worse than the other and it's not lube related as I use top shelf oil and change it often.

Could be a myth, but I wont ever run them on the exhaust side again. JMO

[sfmichael]

As I stated Eric, I am not sure exactly what caused these failures, but they were both hot rods, and both lost the rear exhaust lifter.

The set of SE 1.725 I took off of my bike with about 5k on them both of the exhaust rocker tips had some abnormal wear, one much worse than the other and it's not lube related as I use top shelf oil and change it often.

Could be a myth, but I wont ever run them on the exhaust side again. JMO

interesting

[1FSTRK]

As I stated Eric, I am not sure exactly what caused these failures, but they were both hot rods, and both lost the rear exhaust lifter.

The set of SE 1.725 I took off of my bike with about 5k on them both of the exhaust rocker tips had some abnormal wear, one much worse than the other and it's not lube related as I use top shelf oil and change it often.

Could be a myth, but I wont ever run them on the exhaust side again. JMO

What brand of rocker?
If they all had the same bigger ratio, why would one wear more than the others if the wear was caused by the new ratio?
I do not dispute the problems you had/found, I only question that you blame it on a ratio change.

[Durwood]

As I stated Eric, I am not sure exactly what caused these failures, but they were both hot rods, and both lost the rear exhaust lifter.

The set of SE 1.725 I took off of my bike with about 5k on them both of the exhaust rocker tips had some abnormal wear, one much worse than the other and it's not lube related as I use top shelf oil and change it often.

Could be a myth, but I wont ever run them on the exhaust side again. JMO

What brand of rocker?
If they all had the same bigger ratio, why would one wear more than the others if the wear was caused by the new ratio?
I do not dispute the problems you had/found, I only question that you blame it on a ratio change.

They were new SE non roller rockers. Only running them 5k I removed them when I changed my cams and noticed the wear only on the exhaust rocker tips, one is junk, and the valve tips were fine.
If you remember, I know Stroker does, I contemplated using them on the 57's before I pulled it down.

I reinstalled my stock rockers with the 57's and have had it apart 2 times in the last 16k miles for other reasons, once just a month ago and the stock rockers still look great.

Why ratio? It was a culmination of seeing the failed exhaust lifters, both had 1.7 roller tip rockers, and the abnormal exhaust rocker arm tip wear on mine, I decided not to try them again, at least not on the exhaust side.

Could be a huge coincidence, but one that I will be able to rule out of the equation moving forward.

Daren

[1FSTRK]

Your rockers, one worse than the other sounds like poor quality control at production. If both valve stems were fine than the rockers could have been too soft.

The lifter bikes there is just not enough information to make any type of call what the cause was. For me to come to your conclusion, all bikes with 1.7 on the exhaust would have to ruin both exhaust lifters and they do not. I also have seen many, if not most lifters fail when running stock ratio rockers.

I do not mean to challenge you, I just feel like when things come up and we simply blame a part and move on nothing is solved or learned. Thanks for sharing your experiences with the 1.7's, wish for you it had been better.


Added
Another thing to note on your bike is the valve arm end of the SE 1.7 rocker is identical to the stock one, it is the pushrod cup they move so the contact point and movement on the valve when opening is identical to a stock rocker with a higher lift cam. Just no way the failure was due to the ratio. 

[Don D]

Consider factoring if the valves turn or remain stationary

[Durwood]

Your rockers, one worse than the other sounds like poor quality control at production. If both valve stems were fine than the rockers could have been too soft.

The lifter bikes there is just not enough information to make any type of call what the cause was. For me to come to your conclusion, all bikes with 1.7 on the exhaust would have to ruin both exhaust lifters and they do not. I also have seen many, if not most lifters fail when running stock ratio rockers.

I do not mean to challenge you, I just feel like when things come up and we simply blame a part and move on nothing is solved or learned. Thanks for sharing your experiances with the 1.7's, wish for you it had been better.

Challenge is good. I too wondered about QC but it's funny that the 2 intake rockers were perfect, only the exhaust rockers were affected, rear more than front, maybe someone running them now could take a look to see how theirs are doing.

And the lifter failure was also the rear and could be the front was to follow? who knows as all 4 were changed.

I didn't spend the time to investigate further considering the fact that the higher ratio rockers seem to only help performance on the intake side and have read cases where when used on the exhaust side can actually make the power go backwards.

I still have those rockers and will be more than happy to snap some pics and post them when I am in the shop next week.

[1FSTRK]

It is curious about the intake both being fine. I was thinking about the geometry difference with the exhaust valve being at a different angle than the intake but none of that changes from stock rocker to the SE rocker so that is out. I could see if your bike eat the ball off the pushrod, that contact point is where the change takes place but the pressure and geometry at the valve stays exactly the same with the exception of the extra travel which it the same as adding some cam lift. Just does not makes sense.

One thought, inspect the SE rockers for the angle of the valve oiling hole and the size as well as condition compared to a stock rocker. Maybe a difference there or something not made right.

[kd]

Another consideration may be the difference in exh / int valve tip temp. A good quality oil should handle the difference though.

[1FSTRK]

Another consideration may be the difference in exh / int valve tip temp. A good quality oil should handle the difference though.

Yes that was why I was questioning the oil supply holes. It would not seem that the rocker pad on the stock would be able to handle any higher temp than the rocker pad on the SE.

[Barrett]

 Mine have about 25,000 miles on them with 37's.. Here's a pic of the exhaust rockers.

[converted1]

thanx to ev1 for that info,think I'm gone give em a whirl

[1FSTRK]

TDC lift and valve to valve clearance will be horrendous with a 590 and high ratio rockers.

While I do not agree that another .010-.015 lift at TDC is horrendous, you will want to check all valve clearances as well as the rocker travel at the valve stem and pushrod clearance with this upgrade.

[Matt C]

Id be willing to bet that the extra TDC lift is what's making the difference.
More so than a little more total lift at LCA. Just a theory though... 

There's more degrees of overlap too, that has a huge influence.

[1FSTRK]

With most heads it is the increased area under the total flow curve that makes the difference. More total flow, more overlap flow, all without changing actual valve seat time.

[Matt C]

I get that. My point was to highlight the importance of the overlap event.
It's the most critical event of them all (even though the piston isn't even
moving)

[HD/Wrench]

The issue is that unless all testing is done with X cam specs you are dealing with different lift rates on the cam. X amount of rotation vs amount of lift. so shape of the lobe can be just one thing that will effect how it works or does not work. I have found that the 640 S&S cam does respond to the 1.7 rocker , but that is a pretty mild cam grind wise. now looking at something that is more aggressive my guess is you will not see the same type of increase if any .  with all things equal. But again its back to testing it on that given package.   

[Matt C]

  You're less likely to see the same gains on more aggressive cams.

added: These are a very useful as a tool to tell you if the motor wants more
cam (In and/or Ex)

[1FSTRK]

That too becomes head relative, some port designs will respond better than others. As far as the lobe design goes whether it is the lobe or the rocker ratio doing it we cannot open the valve as fast as we would like without loosing control of the valve in this type of engine anyway.

[Matt C]

Since the head is part of the "motor", what you're saying is true.
How much cam the motor 'wants' is directly related to how well the
heads work (or don't work). The better the heads, the less cam you
need. (generally)

[jam65]

Very interesting theories being stated here. So you think a radical cam will not benefit from using a higher ratio rocker arm?

[No Cents]

       

[Matt C]

 

[CowboyTutt]

Very interesting theories being stated here. So you think a radical cam will not benefit from using a higher ratio rocker arm?

Jam, I'm thinking this might actually be true.  The more the heads flow, the less cam duration and lift is needed.  This has been proven true with Kury heads who shunt the exhaust off early with Kury cams but with great intake flow, or with B2 or B3 heads which seem to need the early closing 635 HO intake cam timing to produce good torque with such big valves and large ports.  Ray's heads flow better than any large port B2 or B3 head, so they need to be considered as any other large flowing head, and he should be looking at reducing his cam timing as he is.  In such high flowing, big port heads, I would be looking to reduce timing events to increase velocity and torque and that includes valve lift. 

Regards,

-Tutt

[jam65]

I understand what you are saying. Some people say that the maximum flow of a certain head is not the end all, be all of the build. Strong mid lift numbers have a major importance in this game as was stated. I know my head porter would not steer me into this situation of using higher ratio rockers if he thought I was going in the wrong direction. I will just have to wait until the finished product makes it to the dyno.

[Don D]

Very interesting theories being stated here. So you think a radical cam will not benefit from using a higher ratio rocker arm?

INDEED!

[No Cents]

 hell "A"...I don't even have any heads on my bike right now.
For almost two months now it's been sitting kind of naked just waiting   ...but it will go back together with 1.725 rollers on the intakes.
I've personally seen and felt gains with 1.725's on the intakes of both the CR651 cams (which has a radical lobe) and more timid S&S 640's. I like what I've personally seen for the results.
I think Scott from Hillside said it best..."the 1.725's are just another tool in your tool box".

Ray

[Don D]

The more the heads flow, the less cam duration and lift is needed

Depends on what the air speed is which the CSA will be part of determining among other factors

This has been proven true with Kury heads CAMS who shunt the exhaust off early with Kury cams but with great intake flow

The heads actually have very strong exhaust flow right off the seat on up, on purpose.

Try the ratio rocker(s), run a test, then decide
This is part of TUNING, not just laptops and software.
Giving the motor what it wants.

Or spend another dozen pages in theory taking bandwidth.

[Matt C]

Very interesting theories being stated here. So you think a radical cam will not benefit from using a higher ratio rocker arm?

Jam, My experience (with dirt circle track motors) showed under camed/under headed motors see the best
gains from higher ratio rockers. Allot of classes don't allow trick heads (or roller cams for that matter)
so they need all the help they can get.

Unlimited engines (fewer rules) you don't need them so much. If your heads are really good, you don't
need as much duration to fill the cylinders at a given rpm. This gives a much flatter torque curve, better low
end manners while still running out strong on the top. Bigger valve heads also require less overlap, further
helping low end manners.

So, if the heads are inadequate, you'll find yourself looking at huge cams and high ratio rockers to make
up for it. So it's really not the cam by itself that determines weather you can use HR rockers, its the whole
package. It has to all work in harmony, Heads, pipes, cams.

Hope that helps.... mc

PS. As Don points out, port cross sectional area is what determines air speed at a given rpm. So that has
to be right too.

[Don D]

The added lift does nothing if the heads have already flatlined
And that critical balance during overlap can be disturbed if it was close to begin with.
Trial, A and B testing on the same dyno.
Definitive answer no theory

[Matt C]

The added lift does nothing if the heads have already flatlined
And that critical balance during overlap can be disturbed if it was close to begin with.
Trial, A and B testing on the same dyno.
Definitive answer no theory

Yep. Stock heads peter out around .500" (if you're lucky). Anything over a mild cam is a big waste if
your heads are not up to the task. Dyno testing or lap times/ET are the only real ways to know if you're
helping or hurting your cause.

[Matt C]

I think Scott from Hillside said it best..."the 1.725's are just another tool in your tool box".
Ray

I think I said that on page 2 as well...

[1FSTRK]

The funny thing is this debate goes on for all rocker arm engines. Chevy SB had 1.5 and 1.6 the stock LS1 has a rising rate rocker that starts at about 1.5 on the seat and reaches 1.7 at full valve lift, as did the 1967 the 427 Ford and Big block chevys were 1.7 at the time. Harley has run 1.43, 1.5, 1.62 just in the last three rocker designs.

How exactly does one determine that the present HD stock ratio is perfect and the only right ratio for all Twin cam engines regardless of cam grind, displacement, and port flow, both volume and speed?

As long as you do not loose control of the valve the way in which you open the valve as fast as possible really does not matter. Just like every other time this comes up the answer is test it on the dyno, the simulators will just not cut it for this type of thing. I have seen all types of engines have all types of responses. Saw a World of Outlaws injected engine come in from the builder with 1.6 ratio rollers and leave the dyno with 1.8 on the intake and 1.5 on the exhaust, oh and it picked up 85hp.

Do the test, the rest of this is just bar room talk without the pretty girls.

[N-gin]

I believe VDOP from another forum was thinking of 1.7 with his 266e cams. At the time his numbers were 145/133t, from a 113 and DVR head, 2.1/1.65. Don't know what came of it the post kind of fizzled away.

[strokerjlk]

As I stated Eric, I am not sure exactly what caused these failures, but they were both hot rods, and both lost the rear exhaust lifter.

The set of SE 1.725 I took off of my bike with about 5k on them both of the exhaust rocker tips had some abnormal wear, one much worse than the other and it's not lube related as I use top shelf oil and change it often.

Could be a myth, but I wont ever run them on the exhaust side again. JMO

What brand of rocker?
If they all had the same bigger ratio, why would one wear more than the others if the wear was caused by the new ratio?
I do not dispute the problems you had/found, I only question that you blame it on a ratio change.

They were new SE non roller rockers. Only running them 5k I removed them when I changed my cams and noticed the wear only on the exhaust rocker tips, one is junk, and the valve tips were fine.
If you remember, I know Stroker does, I contemplated using them on the 57's before I pulled it down.

I reinstalled my stock rockers with the 57's and have had it apart 2 times in the last 16k miles for other reasons, once just a month ago and the stock rockers still look great.

Why ratio? It was a culmination of seeing the failed exhaust lifters, both had 1.7 roller tip rockers, and the abnormal exhaust rocker arm tip wear on mine, I decided not to try them again, at least not on the exhaust side.

Could be a huge coincidence, but one that I will be able to rule out of the equation moving forward.

Daren

both engines running the same lifters ?
Ex valve is harder to open than the intake.

What came first the chicken or the egg ?  ( lifter or rocker arm )

[1FSTRK]

As I stated Eric, I am not sure exactly what caused these failures, but they were both hot rods, and both lost the rear exhaust lifter.

The set of SE 1.725 I took off of my bike with about 5k on them both of the exhaust rocker tips had some abnormal wear, one much worse than the other and it's not lube related as I use top shelf oil and change it often.

Could be a myth, but I wont ever run them on the exhaust side again. JMO

What brand of rocker?
If they all had the same bigger ratio, why would one wear more than the others if the wear was caused by the new ratio?
I do not dispute the problems you had/found, I only question that you blame it on a ratio change.

They were new SE non roller rockers. Only running them 5k I removed them when I changed my cams and noticed the wear only on the exhaust rocker tips, one is junk, and the valve tips were fine.
If you remember, I know Stroker does, I contemplated using them on the 57's before I pulled it down.

I reinstalled my stock rockers with the 57's and have had it apart 2 times in the last 16k miles for other reasons, once just a month ago and the stock rockers still look great.

Why ratio? It was a culmination of seeing the failed exhaust lifters, both had 1.7 roller tip rockers, and the abnormal exhaust rocker arm tip wear on mine, I decided not to try them again, at least not on the exhaust side.

Could be a huge coincidence, but one that I will be able to rule out of the equation moving forward.

Daren

both engines running the same lifters ?
Ex valve is harder to open than the intake.

What came first the chicken or the egg ?  ( lifter or rocker arm )

Yes but he has 100 lbs of tq and 1.7 ratio what about the engines with 150 lbs tq and stock 1.62 ratio their ex valve sees a much higher cylinder pressure to open against.

[Don D]

Depends on where the exhaust opens.

[1FSTRK]

Depends on where the exhaust opens.

So you are on record as stating a 150 hp engine will have an exhaust valve opening at a time in the power stroke that will have less chamber pressure than Darren's engine with the 57H cams, right?

We are talking real world here not some imaginary cam that opens at 5 degrees BBDC

[Don D]

This is all theory Eric
Move the exhaust earlier and pressure drops. Right?
As far as Darren's failure, it is exhaust and opens under pressure stacked on the pressures you already mentioned. OK fine and dandy or not if the materials such as the valve stem tip or rocker tip are not hard enough. Materials do count and quality is not always consistent.
But haven't we strayed from the topic?

[1FSTRK]

This is all theory Eric
Move the exhaust earlier and pressure drops. Right?

Are you sure?
Opening the exhaust valve earlier in the combustion stroke will decrease the pressure the rocker has to over come?


Added
I see you added to your post while I was typing my reply to the original one. I will get to the additions you made right after you answer this post.

[strokerjlk]

As I stated Eric, I am not sure exactly what caused these failures, but they were both hot rods, and both lost the rear exhaust lifter.

The set of SE 1.725 I took off of my bike with about 5k on them both of the exhaust rocker tips had some abnormal wear, one much worse than the other and it's not lube related as I use top shelf oil and change it often.

Could be a myth, but I wont ever run them on the exhaust side again. JMO

What brand of rocker?
If they all had the same bigger ratio, why would one wear more than the others if the wear was caused by the new ratio?
I do not dispute the problems you had/found, I only question that you blame it on a ratio change.

They were new SE non roller rockers. Only running them 5k I removed them when I changed my cams and noticed the wear only on the exhaust rocker tips, one is junk, and the valve tips were fine.
If you remember, I know Stroker does, I contemplated using them on the 57's before I pulled it down.

I reinstalled my stock rockers with the 57's and have had it apart 2 times in the last 16k miles for other reasons, once just a month ago and the stock rockers still look great.

Why ratio? It was a culmination of seeing the failed exhaust lifters, both had 1.7 roller tip rockers, and the abnormal exhaust rocker arm tip wear on mine, I decided not to try them again, at least not on the exhaust side.

Could be a huge coincidence, but one that I will be able to rule out of the equation moving forward.

Daren

both engines running the same lifters ?
Ex valve is harder to open than the intake.

What came first the chicken or the egg ?  ( lifter or rocker arm )

Yes but he has 100 lbs of tq and 1.7 ratio what about the engines with 150 lbs tq and stock 1.62 ratio their ex valve sees a much higher cylinder pressure to open against.

I would think the spring pressure on the 150 hp motor would effect the pressure of the valve opening more .
The 204 was cranking well over 200 CCP IIRC .
Put a cheap lifter in the front exhaust with heavy nose pressure  , if you want to see how well it stays pumped up .

The fact that both ex rockers and ex lifters were trashed throws up a flag to me .
Was the lifter providing enough lubercant to the top end ?
Did the lifter become so weak that it couldn't pump enough oil to the top end . ( ex lifters would go first )
Did the particles from the trashed rollers get pumped to the rockers ?
I am betting that all 4 lifters were getting weak . The two that take the  most abuse went first .
Was it the 1.7 rockers fault? I doubt they helped the situation .

[Durwood]

As I stated Eric, I am not sure exactly what caused these failures, but they were both hot rods, and both lost the rear exhaust lifter.

The set of SE 1.725 I took off of my bike with about 5k on them both of the exhaust rocker tips had some abnormal wear, one much worse than the other and it's not lube related as I use top shelf oil and change it often.

Could be a myth, but I wont ever run them on the exhaust side again. JMO

What brand of rocker?
If they all had the same bigger ratio, why would one wear more than the others if the wear was caused by the new ratio?
I do not dispute the problems you had/found, I only question that you blame it on a ratio change.

They were new SE non roller rockers. Only running them 5k I removed them when I changed my cams and noticed the wear only on the exhaust rocker tips, one is junk, and the valve tips were fine.
If you remember, I know Stroker does, I contemplated using them on the 57's before I pulled it down.

I reinstalled my stock rockers with the 57's and have had it apart 2 times in the last 16k miles for other reasons, once just a month ago and the stock rockers still look great.

Why ratio? It was a culmination of seeing the failed exhaust lifters, both had 1.7 roller tip rockers, and the abnormal exhaust rocker arm tip wear on mine, I decided not to try them again, at least not on the exhaust side.

Could be a huge coincidence, but one that I will be able to rule out of the equation moving forward.

Daren

both engines running the same lifters ?
Ex valve is harder to open than the intake.

What came first the chicken or the egg ?  ( lifter or rocker arm )

Yes but he has 100 lbs of tq and 1.7 ratio what about the engines with 150 lbs tq and stock 1.62 ratio their ex valve sees a much higher cylinder pressure to open against.

I would think the spring pressure on the 150 hp motor would effect the pressure of the valve opening more .
The 204 was cranking well over 200 CCP IIRC .
Put a cheap lifter in the front exhaust with heavy nose pressure  , if you want to see how well it stays pumped up .

The fact that both ex rockers and ex lifters were trashed throws up a flag to me .
Was the lifter providing enough lubercant to the top end ?
Did the lifter become so weak that it couldn't pump enough oil to the top end . ( ex lifters would go first )
Did the particles from the trashed rollers get pumped to the rockers ?
I am betting that all 4 lifters were getting weak . The two that take the  most abuse went first .
Was it the 1.7 rockers fault? I doubt they helped the situation .

I only had an EX rocker issue with my bike, my lifters were good.

The bike with a lifter issue was a friends.

[strokerjlk]

Ahh . Carry on .
< great taste > < less filling >

[pwmorris]

Very interesting theories being stated here. So you think a radical cam will not benefit from using a higher ratio rocker arm?

Jam, I'm thinking this might actually be true.  The more the heads flow, the less cam duration and lift is needed.  This has been proven true with Kury heads who shunt the exhaust off early with Kury cams but with great intake flow, or with B2 or B3 heads which seem to need the early closing 635 HO intake cam timing to produce good torque with such big valves and large ports.  Ray's heads flow better than any large port B2 or B3 head, so they need to be considered as any other large flowing head, and he should be looking at reducing his cam timing as he is.  In such high flowing, big port heads, I would be looking to reduce timing events to increase velocity and torque and that includes valve lift. 

Regards,

-Tutt

You sure about that? 
As Ray said, not sure even he agrees with that...lol
Anyway, my experience has been just the opposite-the better the heads and bigger the cam I have had to work with, combined with a compression bump and all other parts working together, the better results I have had with increasing rocker ratios. The motors have seemed to like it. I've never been good with theory, but I sure love to test stuff out...

[PanHeadRed]

better ...heads.... bigger.... cam.... a compression bump..... better results....with increasing rocker ratios.

Now you done done it.

[No Cents]

better ...heads.... bigger.... cam.... a compression bump..... better results....with increasing rocker ratios.

Now you done done it.

     
Red...that will get something started.

  Paul...my heads did flow some respectful numbers before...but nothing like a loved on set of B2/B3 head would.
From what I'm being told my heads will be even better than before when I get them back this time. The valves were picked up today from being coated...which I wasn't even aware to the fact that they were being coated. Fred said the heads will run much cooler with the coating on the valves. 
 
Ray

[pwmorris]

better ...heads.... bigger.... cam.... a compression bump..... better results....with increasing rocker ratios.

Now you done done it.

     
Red...that will get something started.

  Paul...my heads did flow some respectful numbers before...but nothing like a loved on set of B2/B3 head would.
From what I'm being told my heads will be even better than before when I get them back this time. The valves were picked up today from being coated...which I wasn't even aware to the fact that they were being coated. Fred said the heads will run much cooler with the coating on the valves. 
 
Ray

[strokerjlk]

better ...heads.... bigger.... cam.... a compression bump..... better results....with increasing rocker ratios.

Now you done done it.

pump..... pump up the volume. 

[CowboyTutt]

Ray and Paul, two of my best friends here and always grateful for your input from both of you.  You make my Harley world a better place!  I'm no head porter as you both know so darn well, but as a general rule of thumb running higher lift rocker ratios on the intake seems to be a good thing if the intake flow of the heads don't flat line earlier as Don mentioned in one of his posts I believe. 

Now running higher lift ratios on the exhaust flow seems a trickier condition to me, and depending on so many variables, how the exhaust flows on the heads, the exhaust cam timing and lift, the exhaust ports and exhaust itself.  Wow.  Lots to consider on the exhaust side. 

Don consulted with Mike Roland about heads and stuff for my build and Mike told him "run the most intake lift feasible" for a good set of intake flowing heads IIRC.  The exhaust equation was trickier because exhaust lift and duration needed was based upon how well the exhaust port already flowed, how large the engine was, and how the pipe flow was matched to the engine build. 

I don't understand all this stuff myself, but I think my friend Don does and hopefully he can articulate it better than I have. 

That being said, I don't think a radical cam will benefit from increased rocker ratios as much if the cam is already very aggressive in intake lift and short duration.  A milder grind like a S&S 640 or 635 HO in particular might benefit from higher ratios on the intake side (the 635 certainly does with the 143 engine!) but I'm not sure if the exhaust will in very large builds with high flowing exhaust heads. 

Hey, I leave it up to your engine builders like Don, and Ray and Paul through their engine builders!  But I would suspect that Jamie at FM would agree that everything needs to be beta tested and the combination has to work as a whole. 

Very glad to have such knowledgeable friends here who inspired me.  My engine is basically done, now just trying to upgrade all the other parts necessary to make it hold together and run cool.  That requires a lot money too.  Sigh.   

Regards to the group, but Don, Ray and Paul most of all.  Maybe Ray most of all for him inspiring me (although I'm broke for years because of him!!!!  LOL)

Keep on keeping on Brothers!   

-A- 

[Admiral Akbar]

Ray and Paul, two of my best friends here and always grateful for your input from both of you.  You make my Harley world a better place!  I'm no head porter as you both know so darn well, but as a general rule of thumb running higher lift rocker ratios on the intake seems to be a good thing if the intake flow of the heads don't flat line earlier as Don mentioned in one of his posts I believe. 

Now running higher lift ratios on the exhaust flow seems a trickier condition to me, and depending on so many variables, how the exhaust flows on the heads, the exhaust cam timing and lift, the exhaust ports and exhaust itself.  Wow.  Lots to consider on the exhaust side. 

Don consulted with Mike Roland about heads and stuff for my build and Mike told him "run the most intake lift feasible" for a good set of intake flowing heads IIRC.  The exhaust equation was trickier because exhaust lift and duration needed was based upon how well the exhaust port already flowed, how large the engine was, and how the pipe flow was matched to the engine build. 

I don't understand all this stuff myself, but I think my friend Don does and hopefully he can articulate it better than I have. 

You definitely don't.. There is a point where you can have too much intake..

It's all about matching the flow demands to the motor.

[N-gin]

So having a higher ratio rocker increases valve speed /lift/RPM as well as the additional lift, but what If the heads start to Peter out at say .55-.6, however max flow is .3-.55 lift  and you have a .590 lift cam, would the faster valve speed hit the sweet spot quicker adding more air sooner. Given piston speed is met at that exact moment?
Would there be a performance gain then?

[1FSTRK]

So having a higher ratio rocker increases valve speed /lift/RPM as well as the additional lift, but what If the heads start to Peter out at say .55-.6, however max flow is .3-.55 lift  and you have a .590 lift cam, would the faster valve speed hit the sweet spot quicker adding more air sooner. Given piston speed is met at that exact moment?
Would there be a performance gain then?

Now you are seeing some of the theory. There are many factors and most people think increasing rocker ratio is about getting more lift and the lift is the smallest contributor in the gains if you have gains.

[PanHeadRed]

 max flow is .3-.55 lift 

If your heads hit max flow @ .3" lift and are stalled up to your max of .55" lift, all the rocker arms/cams in the world will not correct the problem of those heads.

[Barrett]

I was told the 1.725's on the EX would be too much flow w/55's by the same guy who said I need larger EX valves.. Can someone explain that one to me?

[Don D]

Ray and Paul, two of my best friends here and always grateful for your input from both of you.  You make my Harley world a better place!  I'm no head porter as you both know so darn well, but as a general rule of thumb running higher lift rocker ratios on the intake seems to be a good thing if the intake flow of the heads don't flat line earlier as Don mentioned in one of his posts I believe. 

Now running higher lift ratios on the exhaust flow seems a trickier condition to me, and depending on so many variables, how the exhaust flows on the heads, the exhaust cam timing and lift, the exhaust ports and exhaust itself.  Wow.  Lots to consider on the exhaust side. 

Don consulted with Mike Roland about heads and stuff for my build and Mike told him "run the most intake lift feasible" for a good set of intake flowing heads IIRC.  The exhaust equation was trickier because exhaust lift and duration needed was based upon how well the exhaust port already flowed, how large the engine was, and how the pipe flow was matched to the engine build. 

I don't understand all this stuff myself, but I think my friend Don does and hopefully he can articulate it better than I have. 

You definitely don't.. There is a point where you can have too much intake..

It's all about matching the flow demands to the motor.

Absolutely right on
Andy my conversation with MR was very specifically constrained to your motor in the context of using a certain wild things cam
That is the problem with a lot of these theory exercises, a component gets examined with a brush far too wide.

[1FSTRK]

max flow is .3-.55 lift 

If your heads hit max flow @ .3" lift and are stalled up to your max of .55" lift, all the rocker arms/cams in the world will not correct the problem of those heads.

But this is a rocker thread, so given he has sub standard heads will rockers help them out or not?

[PanHeadRed]

There is potential, I would be surprised if they did not.

[CowboyTutt]

Don and Max, thanks guys.  I believe Don this is why you thought my intake manifold did not need more reworking as it flows plenty to feed the engine.  It could maybe flow more on a flow bench but that would not necessarily benefit the engine.  Would that be correct?  Thanks for taking the time to correct me, just trying to get the right information out there.  -A-

[1FSTRK]

There is potential, I would be surprised if they did not.

I agree.
At this point the next step would be a good back to back test on the dyno with a tuner that has some R&D experience. Many times things get run on the dyno this year, multiple changes get made and it is back to the dyno next year for a run and there is no way to tell what change had what effect. Rocker changes are tuning for the valve train, look at it just like timing, or jetting.

[bulldog68]

I am considering trying them on the intake side

[PanHeadRed]

What is up with this only on the intake stuff? Where does that come from?

There really is performance value in getting the fired charge out to make more room for the new.

Just because the exhaust is evacuated under pressure does not automatically mean one has maximized it's potential to facilitate cylinder fill. HD's exhaust is designed to limit emissions out put not maximize performance. The quicker you snap the exhaust valve open the greater the pressure differential. In simple terms all your really trying to accomplish with this stuff is keep pressure differential as great as possible for as long as possible.

I don't understand why the exhaust side is so overlooked, taken for granted and under valued as part of the system.

[86fxwg]

I was told the 1.725's on the EX would be too much flow w/55's by the same guy who said I need larger EX valves.. Can someone explain that one to me?

86

[1FSTRK]

What is up with this only on the intake stuff? Where does that come from?

There really is performance value in getting the fired charge out to make more room for the new.

Just because the exhaust is evacuated under pressure does not automatically mean one has maximized it's potential to facilitate cylinder fill. HD's exhaust is designed to limit emissions out put not maximize performance. The quicker you snap the exhaust valve open the greater the pressure differential. In simple terms all your really trying to accomplish with this stuff is keep pressure differential as great as possible for as long as possible.

I don't understand why the exhaust side is so overlooked, taken for granted and under valued as part of the system.

I can only speak for what I have seen, but I have never seen an exhaust only ratio increase anything. I have seen many times that just on the intakes helps and about half again as many times that adding ratio to both helped. It is not that it is not looked at and tested, it seems it does not yet need additional improvements to keep up.

I will also add that I have not seen gains from the bigger exhaust valve that everyone likes to install. Vic used the stock 96" casting with HD valve, seat and rocker on my 110". It just looks to me like the exhaust side was either sufficient or perhaps a little big to begin with.

[PanHeadRed]

the exhaust side was either sufficient or perhaps a little big to begin with.

No argument, in relation to what, all applications?

Care to share your ex flow rates, port size, and valve lift?

[Don D]

Lol
Consider where you are at in the cycle where that added lift is applied. I see benefits in opening quicker but lift, not so much.
Often overlooked and especially so when cams are advanced is the very important exhaust opening point. And red is right, the goal is to accomplish pressure differential by exhaust scavenging. Then we get better filling by means of an intake with proper port geometry.

[1FSTRK]

Depends on where the exhaust opens.

So you are on record as stating a 150 hp engine will have an exhaust valve opening at a time in the power stroke that will have less chamber pressure than Darren's engine with the 57H cams, right?

We are talking real world here not some imaginary cam that opens at 5 degrees BBDC

This is all theory Eric
Move the exhaust earlier and pressure drops. Right?

Are you sure?
Opening the exhaust valve earlier in the combustion stroke will decrease the pressure the rocker has to over come?

Before you start in another direction could we finish with this post you made?

[1FSTRK]

the exhaust side was either sufficient or perhaps a little big to begin with.

No argument, in relation to what, all applications?

Care to share your ex flow rates, port size, and valve lift?

We all know it is a relationship so naturally it could not be enough in all applications.
I can say that the best running 74" sportsters I have witnessed all started with original 883 heads and retained the original exhaust seats. I know that my 110" 130/130 makes more with the original 96" castings and exhaust seats then the reworked SE110 heads the kit came with. I am not talking just a peak number, this is HP/CI, TQ/CI, area under the tq curve and required cam duration and static compression.

There is of coarse a point where you will need to increase the exhaust, bigger cam lobe, faster ratio, bigger valve, but until I see signs of it falling behind or see the exhaust increases help we have not needed to.

The early small block chevys needed help on the exhaust side and every time you improved them you gained. Later when the after market heads appeared they were already fixed when you got them. The example I mentioned in an earlier post had aftermarket heads that had been worked on ( because more has always been better right) that was the engine that they took the 1.6 ratio off the exhaust and put 1.5 on and it picked up. Took the 1.6 off the intake, put 1.8's on and picked up more. More intake area under the curve helps but the fact it wanted up on intake ratio and down on exhaust ratio to gain power would indicate the balance was off. These guys would have 4 or 5 cams ground and bring them to the dyno for testing (V-8 test cams for $110 a pop and have them in 5 days not like the HD stuff we put up with). They pulled the head checked them on the bench and they simply had the best SB exhaust numbers they had ever seen so I have seen engine combo gain from exhaust work and loose from to much exhaust work.

[Don D]

the exhaust side was either sufficient or perhaps a little big to begin with.

No argument, in relation to what, all applications?

Care to share your ex flow rates, port size, and valve lift?

Care to share your flows, throat size, valve size and lift, exhaust side

[strokerjlk]

[PanHeadRed]

the exhaust side was either sufficient or perhaps a little big to begin with.

No argument, in relation to what, all applications?

Care to share your ex flow rates, port size, and valve lift?

Care to share your flows, throat size, valve size and lift, exhaust side

I poke a 1.4" diameter hole, and cut a seat for 1.61" valve, @ 28" / .6" lift  it yields 220+ on 99 style castings and 240+ on the 06 up's

[Admiral Akbar]

I know that my 110" 130/130 makes more with the original 96" castings and exhaust seats then the reworked SE110 heads the kit came with. I am not talking just a peak number, this is HP/CI, TQ/CI, area under the tq curve and required cam duration and static compression.

This agrees with my Tail of 2 heads.. Head flow and cam need to be matched to displacement.. IMO 110 heads are really to big for a 110.. Look at what Wess (tattoo) is getting with SE cnc ported stock castings in 110s.. The only way you are going to get the 110 to produce a better power band (if possible) is to spin the motor to 8K.. 

[PanHeadRed]

We all know it is a relationship so naturally it could not be enough in all applications.

Agreed, so where does this "Intake only" come from?

What's the absolute 1st thing we do as a community for performance? Yeah, improve exhaust flow, most times before it leaves the dealer, why? because we KNOW improving the exhaust will improve performance.  At some point there will be a diminishing return on the effort, we can all agree on that,  but on an unknown combo who has the wisdom and foresight to determine that point from behind a computer 50 states away?

The exhaust is a pretty common choke point for a lot of builds.

[PanHeadRed]

I know that my 110" 130/130 makes more with the original 96" castings and exhaust seats then the reworked SE110 heads the kit came with. I am not talking just a peak number, this is HP/CI, TQ/CI, area under the tq curve and required cam duration and static compression.

This agrees with my Tail of 2 heads.. Head flow and cam need to be matched to displacement.. IMO 110 heads are really to big for a 110.. Look at what Wess (tattoo) is getting with SE cnc ported stock castings in 110s.. The only way you are going to get the 110 to produce a better power band (if possible) is to spin the motor to 8K.. 

255 Cam.

[Admiral Akbar]

I know that my 110" 130/130 makes more with the original 96" castings and exhaust seats then the reworked SE110 heads the kit came with. I am not talking just a peak number, this is HP/CI, TQ/CI, area under the tq curve and required cam duration and static compression.

This agrees with my Tail of 2 heads.. Head flow and cam need to be matched to displacement.. IMO 110 heads are really to big for a 110.. Look at what Wess (tattoo) is getting with SE cnc ported stock castings in 110s.. The only way you are going to get the 110 to produce a better power band (if possible) is to spin the motor to 8K.. 

255 Cam.

Yep that helps..  But the heads are severely neutered on the top..

[HD/Wrench]

IF we take out the head flow and lets look at just testing to see what happens. In fact I do have head flow on some of the testing we did but all we can do is say rule of thumb??  So we had a 107 CI bike with stock heads and a Woods 6 cam. We ran it with stock rockers and it made X with 1.7 on the intake we did pick a few across the board. When we installed the 1.7 on the ex we lost low end tq curve and it stayed very close to the same from 3500 RPM on up.  Now the same test with a T man 625 in another 107 with RR stage V cast Hp heads the 1.7 did nothing at all on either side. The same build with a S&S 585 did respond to the 1.7 on intake went backwards with it on the ex side. Same build with a Crane 296 1.7 on in did nothing, on the ex side it did pull the tq curve our further but no gains in peak numbers or even the curve just a bit quicker coming in and held on a few more hundred further.

I feel that in most cases the ex side of the cam is a main issue with building power due to when or how soon to be more accurate it opens. The crane 296 and the S&S are very close intake wise but the ex is nothing alike. back to back holding on to the cylinder charge produce more hp and more tq in that given build. 

Each one is different with stock heads I feel you can get a more close test subject but even then you have flow changes.   Testing did not prove or dis prove anything other than each package may or may not respond to it. What I thought would happen was not the case per say.

[1FSTRK]

Rocker changes are tuning for the valve train, look at it just like timing, or jetting.

IF we take out the head flow and lets look at just testing to see what happens. In fact I do have head flow on some of the testing we did but all we can do is say rule of thumb??  So we had a 107 CI bike with stock heads and a Woods 6 cam. We ran it with stock rockers and it made X with 1.7 on the intake we did pick a few across the board. When we installed the 1.7 on the ex we lost low end tq curve and it stayed very close to the same from 3500 RPM on up.  Now the same test with a T man 625 in another 107 with RR stage V cast Hp heads the 1.7 did nothing at all on either side. The same build with a S&S 585 did respond to the 1.7 on intake went backwards with it on the ex side. Same build with a Crane 296 1.7 on in did nothing, on the ex side it did pull the tq curve our further but no gains in peak numbers or even the curve just a bit quicker coming in and held on a few more hundred further.

I feel that in most cases the ex side of the cam is a main issue with building power due to when or how soon to be more accurate it opens. The crane 296 and the S&S are very close intake wise but the ex is nothing alike. back to back holding on to the cylinder charge produce more hp and more tq in that given build. 

Each one is different with stock heads I feel you can get a more close test subject but even then you have flow changes.   Testing did not prove or dis prove anything other than each package may or may not respond to it. What I thought would happen was not the case per say.

And once you have enough experience with a particular package you know what to recommend.

[1FSTRK]

Many head designs use two smaller exhaust valves, it will allow for quicker exhaust which requires less exhaust duration and that makes more room for the bigger intake with the extra intake duration they needed to make more power. The same thing Mike Roland did only taking it to the next level.

[1FSTRK]

We all know it is a relationship so naturally it could not be enough in all applications.

Agreed, so where does this "Intake only" come from?

What's the absolute 1st thing we do as a community for performance? Yeah, improve exhaust flow, most times before it leaves the dealer, why? because we KNOW improving the exhaust will improve performance.  At some point there will be a diminishing return on the effort, we can all agree on that,  but on an unknown combo who has the wisdom and foresight to determine that point from behind a computer 50 states away?

The exhaust is a pretty common choke point for a lot of builds.

But what evidence can you give that we have reached the point of out growing the stock seat and valve.
As for the wisdom I have seen the losses or lack of gains in many tests on various size Twin cam engines when increasing exhaust.

I have seen extensive testing where the 54"(883) has grow to 74", 80", 88" using the same engine, cams, and proportional increase on the intake flow only and continued to make top power curves and HP/CI with no exhaust valve or flow changes from the original 883 ported stock size seat. Different free flowing test exhaust were tried on each combo, each yield comparable curve shapes as displacement increased.

This same type of testing went into the TW88, 95", 97" and again for the 96"103" and 110" all with the same outcome. In the end the relationship of the exhaust valve to the engine size for both engine groups yielded the same information in regard for the need to retain or increase the stock ex size. 

[HD/Wrench]

Rocker changes are tuning for the valve train, look at it just like timing, or jetting.

IF we take out the head flow and lets look at just testing to see what happens. In fact I do have head flow on some of the testing we did but all we can do is say rule of thumb??  So we had a 107 CI bike with stock heads and a Woods 6 cam. We ran it with stock rockers and it made X with 1.7 on the intake we did pick a few across the board. When we installed the 1.7 on the ex we lost low end tq curve and it stayed very close to the same from 3500 RPM on up.  Now the same test with a T man 625 in another 107 with RR stage V cast Hp heads the 1.7 did nothing at all on either side. The same build with a S&S 585 did respond to the 1.7 on intake went backwards with it on the ex side. Same build with a Crane 296 1.7 on in did nothing, on the ex side it did pull the tq curve our further but no gains in peak numbers or even the curve just a bit quicker coming in and held on a few more hundred further.

I feel that in most cases the ex side of the cam is a main issue with building power due to when or how soon to be more accurate it opens. The crane 296 and the S&S are very close intake wise but the ex is nothing alike. back to back holding on to the cylinder charge produce more hp and more tq in that given build. 

Each one is different with stock heads I feel you can get a more close test subject but even then you have flow changes.   Testing did not prove or dis prove anything other than each package may or may not respond to it. What I thought would happen was not the case per say.

And once you have enough experience with a particular package you know what to recommend.

[strokerjlk]

I know that my 110" 130/130 makes more with the original 96" castings and exhaust seats then the reworked SE110 heads the kit came with. I am not talking just a peak number, this is HP/CI, TQ/CI, area under the tq curve and required cam duration and static compression.

This agrees with my Tail of 2 heads.. Head flow and cam need to be matched to displacement.. IMO 110 heads are really to big for a 110.. Look at what Wess (tattoo) is getting with SE cnc ported stock castings in 110s.. The only way you are going to get the 110 to produce a better power band (if possible) is to spin the motor to 8K.. 

255 Cam.

Been saying that myself forever . No one ever listens .

Just my observations . More directed toward Bruce
Stock 110 heads will go 120 square on a 110 with 10.5 compression . Will a stock 96 head do that ?   
I haven't had the fortune of ever using/ seeing a stock 88-103 ci 99-2013 casting head, that was ported and I felt would make the power of a good ported 110 head .

Personally IMO , based on the stuff I have tuned . And I have tuned most everyone's heads at one point ...... Currently the choke is intake manifold flow and EX port flow .
Whoever takes the EX port to the next level will be a busy man .

[Don D]

Dave's heads had an exhaust port reduction. Hopefully he will get it to you later this year. He is happy with it.

[PanHeadRed]

But what evidence can you give that we have reached the point of out growing the stock seat and valve.

None. I have absolutely no clue, the OP stated he has a TM 590 cam, that's it, all the info I got, hell I don't even know what displacement the engine is or any other details, from there the technical posts came from every direction abut how HRR's only work on the intake side, he's got the wrong cam, he going to blow up the lifters, to much spring pressure, to much intake etc....WTF?

So I'm not sure were having the same discussion. Are we still discussing the issue of stating HRR's on the exhaust valves absolutely wont work without trying or even knowing the details of the engine and attached components?

Did we ever figure out if the HRR's are a benefit on the IN valves?

I think the thread got sideways.

EDIT: My comment about the exhaust being the choke point was: There are more 95" and 103" builds with stock heads then ported heads.

[1FSTRK]

But what evidence can you give that we have reached the point of out growing the stock seat and valve.

None. I have absolutely no clue, the OP stated he has a TM 590 cam, that's it, all the info I got, hell I don't even know what displacement the engine is or any other details, from there the technical posts came from every direction abut how HRR's only work on the intake side, he's got the wrong cam, he going to blow up the lifters, to much spring pressure, to much intake etc....WTF?

So I'm not sure were having the same discussion. Are we still discussing the issue of stating HRR's on the exhaust valves absolutely wont work without trying or even knowing the details of the engine and attached components?

Did we ever figure out if the HRR's are a benefit on the IN valves?

I think the thread got sideways.

Sideways 
It is winter on HTT this is how every thread ends up.

[Admiral Akbar]

Been saying that myself forever . No one ever listens .

Just my observations . More directed toward Bruce
Stock 110 heads will go 120 square on a 110 with 10.5 compression . Will a stock 96 head do that ?   
I haven't had the fortune of ever using/ seeing a stock 88-103 ci 99-2013 casting head, that was ported and I felt would make the power of a good ported 110 head .

Personally IMO , based on the stuff I have tuned . And I have tuned most everyone's heads at one point ...... Currently the choke is intake manifold flow and EX port flow .
Whoever takes the EX port to the next level will be a busy man .

Not sure what you been saying forever..

But you should know what I been saying forever..  But its got a flatland TQ curve... 

First won't argue that 110 heads make more power and TQ but it will have a flatland power band.. Been a while since I looked but there are a number of modified stock castings in 107s that make 120/120 and they typically have better power bands..   For me, I want something that gives a nicer linear throttle response and  still make the numbers up top.. It can be done but it takes a bunch of work to match things up.. If you use bigger ports than needed, you have to cut cam timing to get the velocity up.. That works but then the flow is too high at higher RPM and you lose power.. (Why I said the 255 works for the low end)..  You can increase compression to get upper end net flow up but then you are dealing with higher CCPs and more critical timing..

IMO you can take a 2.1 inch valved head, put it on a range of displacements but expect it to have the same foot-pound per cubic inch across the power band.  Sure it will make HP.. Flow makes HP..   

[strokerjlk]

It don't always have a flatland curve .
You can make it that way ( de tune ) if you want to lose hp/tq .

I though the OP was a wash a day ago . If you think you can come to any real conclusion on the forum , think again . It has to be tested . And if it gains or loses  It will be very little , and not worth most guys time/ money to find out for sure . Especially the level of build we are talking about here .
Carry on. But the sideways conversation was more interesting   

O - yeah .. I was talking stock head Bruce not modified

[Admiral Akbar]

It don't always have a flatland curve .
You can make it that way ( de tune ) if you want to lose hp/tq .

I though the OP was a wash a day ago . If you think you can come to any real conclusion on the forum , think again . It has to be tested . And if it gains or loses  It will be very little , and not worth most guys time/ money to find out for sure . Especially the level of build we are talking about here .
Carry on. But the sideways conversation was more interesting   

O - yeah .. I was talking stock head Bruce not modified

Isn't what's in red a conclusion from this discussion?

[strokerjlk]

It don't always have a flatland curve .
You can make it that way ( de tune ) if you want to lose hp/tq .

I though the OP was a wash a day ago . If you think you can come to any real conclusion on the forum , think again . It has to be tested . And if it gains or loses  It will be very little , and not worth most guys time/ money to find out for sure . Especially the level of build we are talking about here .
Carry on. But the sideways conversation was more interesting   

O - yeah .. I was talking stock head Bruce not modified

Isn't what's in red a conclusion from this discussion?

Yes ur  honor 

[Bagger]

When I think of exhaust restrictions, I think of: stock exhausts, non-reworked exhaust port, stock exhaust valve.

And cam manufacturers use longer exhaust durations in dual pattern cams to compensate for above restrictions to give the engine more time for exhaust gases to exit.

We can reduce exhaust restrictions by:
1.  Installing free flowing exhaust.
2.  Reworking head exhaust port.
3.  Installing larger than stock exhaust valve.

When the valve first cracks open, that's when the most air-flow velocity occurs, so if all exhaust restrictions have been eliminated, then how much lift is necessary?  Have to take into account the cam's lift .510", .525", .575", .590", .625", .650" etc.  Obviously the benefit of increased rocker arm ratio is the valve is opened a little further and faster, allowing more air to exit out of the engine.  If using a cam with a .625" lift, a higher than stock ratio rocker arm may not be necessary.

From my end user results, if exhaust restrictions have been eliminated, than a higher-ratio rocker arm on the exhaust to increase lift is not beneficial.  The extra lift on the exhaust side can lead to over exhaust scavenging.

And that's why I prefer a single pattern cam profile when I've removed as much exhaust restrictions as I can.

[HD/Wrench]

Yes but its winter for most.. so these threads tend to get extrapolated upon .. Maybe we can run a special moly oil and valve coating to reduce the pressure increase  from the higher ratio , Max can you come up with a excel spread sheet for that     waiting for the +4 thread to come next ..

[Don D]

+4 yes 
Coatings
A "good" Cam 

Bagger you mention "restriction". That is certainly a menace in an exhaust system but it is not safe to assume most of the performance exhausts out there either have eliminated restriction and/or actually scavenge.

[Bagger]

+4 yes 
Coatings
A "good" Cam 

Bagger you mention "restriction". That is certainly a menace in an exhaust system but it is not safe to assume most of the performance exhausts out there either have eliminated restriction and/or actually scavenge.

I agree  There are so many variables to consider. 

Considering valve sizes i.e. my Baisley Superstock Plus heads with 1.94" I / 1.630" E.  I think the exhaust valve is too big, but Baisley, who I've trusted with his years experience thinks otherwise. He may believe the larger the diameter, the more valve area the engine will have to let the burnt gases out.  My exhaust valve is 84.1% the size of my intake valve.

And a thought.  Compression plays a role in valve diameter and valve lift.  Higher compression I think one could use less lift or ratio of the exhaust to intake can be smaller.

[Don D]

I have a set of those heads here now and I went down to 1.61", same valve shape
Flow did not change on the flow bench. 
The goal and motivation however was to fit a larger intake!

[Bagger]

I have a set of those heads here now and I went down to 1.61", same valve shape
Flow did not change on the flow bench. 
The goal and motivation however was to fit a larger intake!

Mentally, a 1.610" exhaust valve would have given me warm and fuzzy feeling.  So with those heads 1.94" intake you used a ratio 83% exhaust to intake valve ratio or did you increase the intake valve size?

[kd]

I have a set of those heads here now and I went down to 1.61", same valve shape
Flow did not change on the flow bench. 
The goal and motivation however was to fit a larger intake!

Ahhhh, but does riding the flow bench compare with years of testing in the engine / on the track experience? I got the same theory from Mr Baisley and got an 81% ratio after a larger exhaust valve was installed. He said the MVA heads were good to go in most ways but the exhaust ports were throw-back evo style and unable to perform at the level the rest of the head could. I, like Bagger, put our trust in the experience this man has. We discussed the recipe (which he took part in creating and testing previous to me contacting him) and he made his recommendations. The bible says to pick a good porter and do what they say. AMEN and pass the biscuits.

Could it be that this discussion about the effect of getting the exhaust valve off the seat quick and getting the flow started fast can be accomplished by up-sizing the exhaust valve appropriately? This statement comes with the caveat that it would be only done to heads that the riding style and performance requirements (RPM range) needed the early evacuation start and it may also be cheaper and easier than extensive port work.

[Don D]

This response seems adversarial or like I am in competition with Dan.
Not so, in fact I spoke to him regarding this change and in the context of this particular build it made sense.
Once again using a more narrow brush and considering the build specifically can provide better results when guys are pushing the higher HP levels.
Times change. We evolve, hopefully. The heads I have were roughly 2009 vintage.

[Admiral Akbar]

It's interest to examine the exhaust valve size but it sort of mimics the rocker arm ratio discussion..  I suspect that exhaust valve nirvana is where you find it.. For instance, a compressionally challenged motor that Bagger mentions probably benefits from a bigger exhaust valve and freer flowing exhaust.. Move the compression up and you have more force driving the exhaust out of the cylinder. Do you need the same sized valve / exhaust flow? Probably not but say you want to increase the RPM limit from 5500 to 7500.. Now you need to do things faster.. Bigger exhaust valve might help.  I don't care what the valve size is as long as it does its job..     

[strokerjlk]

Dave's heads had an exhaust port reduction. Hopefully he will get it to you later this year. He is happy with it.

I was not in any way running anyone's 110 heads down .
There are several guys producing very good 110 ported heads .
They have come a long way since back in 2007 , when most were saying they were junk .

There was a guy that would frequent this site a few years back , that had some stock 99-04 casting heads that was flowing very well , he was making 190 + Hp . ( from AZ I believe )
IIRC. He said they needed constant maintenance .  This holds true with what I have seen at the track with guys running stock casting also .

[kd]

Don, the post was definitely not meant to be adversarial or put you in competition with anyone. The bench comment was a general statement because it seems to be the measure everyone is using to make their point. Maybe it could have been worded better.  I did try to be clear that the comment was in the context of a particular build. I see you agree that it does seem to make sense in this case.  It also backs up the need to test the theory and prove the results.

I have been following this thread without making a comment but the thought of cracking a larger valve off the seat (along with a good multi angle valve job) seemed to me to be an option that no one was mentioning. It is a  fact that the situation with myself (larger Ex Valve recommendation) that I mentioned didn't seem right until I talked to the people involved in the testing and compared the graphs that resulted from the work to more conventional builds.  I hesitated to mention the modification because it is part of a recipe that the porter / builder / tuner put a great deal of time into perfecting. It isn't mine to disclose or even say to much about. If you spoke to Dan about it you likely know that now.   It is a narrow brush but I see this as a narrow brush discussion.

[1FSTRK]

dis·cus·sion
dəˈskəSH(ə)n/
noun
the action or process of talking about something, typically in order to reach a decision or to exchange ideas.
"the proposals are not a blueprint but ideas for discussion"
a conversation or debate about a certain topic.
plural noun: discussions
"discussions about environmental improvement programs"

This is a concept that some do not comprehend.
Any statement not complimentary or in agreement is automatically an attack or  adversarial.

[04 SE Deuce]

Since this thread is seasoned,  I'll throw out what I'm considering.

I've got a couple sets of Kury WT heads, 1.98"/1.63" and all the WT components,  pistons/cams/TB.  One set will go on the FXDXI this year which will be 95",  the other is for when the Deuce needs attention and will be 103".  I have one set of WT46 and 2 sets of WT26 cams and leaning towards using the 26 in both bikes.


Kury TC-26G     Lift    Lift@TDC     Open   Close    Duration    Lope Center
         Intake    .575"     .175"         18       50         248             106
       Exhaust    .495"     .145"         48       14         242             107


Thinking the WT26 cams in the 95" dyna with possibly 1.725 rockers on both intake and exhaust as the heads flow way on up and there is more disparity between the intake and exhaust lift on this cam than any other Kury cam,  or any cam for that matter.

Thought about doing the build with stock rockers,  after tune and plenty of break-in miles do a pull then swap in the 1.725 rockers and re-visit the dyno.  Would measure actual lift with each rocker set.

I tend to ride and not tinker but thought this might be a good application for 1.725 rockers.  Given I ride a fair amount of miles a couple HP probably won't be worth it if maintenance increased much.

Max has and can add the flow numbers on these heads if he likes.

Whata ya think?  -Rick

Add:  FXDXI has newer Bassani Road Rage II with megaphone muffler.

[1FSTRK]

What TB?
As to the rocker test if done correctly it would be a great test to post.

[04 SE Deuce]

Kury 57mm.

[PanHeadRed]

the exhaust side was either sufficient or perhaps a little big to begin with.

No argument, in relation to what, all applications?

Care to share your ex flow rates, port size, and valve lift?

Care to share your flows, throat size, valve size and lift, exhaust side

I poke a 1.4" diameter hole, and cut a seat for 1.61" valve, @ 28" / .6" lift  it yields 220+ on 99 style castings and 240+ on the 06 up's

Don, I posted wrong info, lift is .7" flow rates are: 99-low- mid 230's 06-up high 230's - 240.

[wfolarry]

1.7 rockers & even exhaust valve size are tuning aids in different applications.
Example 1: Low compression. These motors like a later opening exhaust valve because they are building pressure longer so you want to get the most out of it. Now lets bump the compression up with the same cam. Since we can't open it sooner [same cam] going with the 1.7's will open it faster. With a little luck [no way of knowing for sure without testing] we'll make more power. If we go with the 1.7's at the same compression we'll lose power because we lose pressure in the cylinder faster.
Example 2: High compression. Here we want to open the exhaust valve sooner because the pressure in the cylinder is decaying at a faster rate. So with the right cam everything is fine. Putting a 1.7 here will do nothing. Will a bigger exhaust valve help? Maybe. Sometimes bigger valves with the same size throat will flow better because of the chamber shape. So what works in one head doesn't necessarily mean it will work in another. I like to use the smallest chambers possible but that's just me. You'll get arguments that go both ways on that.
The reason why you hear that increasing the ratio on the intake always helps because many believe you can't open the intake fast enough.
On the intake side the pushrod has a straighter shot so you can get away with it. On the exhaust side I think you're pushing your luck.
As far as exhaust lift goes. You don't need as much lift on the exhaust side because by the main event is over sooner but using a lower lift also means you should be using a different spring. Opening it to the same lift means you're just opening into dead space which doesn't hurt anything but you're using the same springs on both sides now. Easier.
As always it's all about the combination of parts. Some make more power than others because everything is complimenting each other. Same as the members here. 
JMO. Maybe I'm wrong. Don't just tell me I'm wrong. Prove it. I like having discussions. 

[1FSTRK]

Larry
I have read in many places and seen in many software programs that peak cylinder pressure needs to happen around 14 degreess after TDC in the power stroke and that after the exhaust valve leaves the seat the cylinder pressure is to low to add any additional power to the piston.  The gasoline burns at a given rate regardless.

Why do you think that a low compression engine will push the piston more degrees after TDC in the power stroke than a high compression engine does?

[John/1]

Zippers had two evo some years back with raise ports intake and exhaust about .500.A 120" and a 131" both had the same cam a redshift 625.The 131 had 1.745 rocker and the 120 had 1.625.I'm only guessing the 131" needed more cam and there next up was a 715 which was to much I guess?
John

[wfolarry]

Larry
I have read in many places and seen in many software programs that peak cylinder pressure needs to happen around 14 degreess after TDC in the power stroke and that after the exhaust valve leaves the seat the cylinder pressure is to low to add any additional power to the piston.  The gasoline burns at a given rate regardless.

Why do you think that a low compression engine will push the piston more degrees after TDC in the power stroke than a high compression engine does?

Slower burn.

[1FSTRK]

Larry
I have read in many places and seen in many software programs that peak cylinder pressure needs to happen around 14 degreess after TDC in the power stroke and that after the exhaust valve leaves the seat the cylinder pressure is to low to add any additional power to the piston.  The gasoline burns at a given rate regardless.

Why do you think that a low compression engine will push the piston more degrees after TDC in the power stroke than a high compression engine does?

Slower burn.

Can you explain why and how much slower.
If not maybe point me to where you got the information so I can look it over.

[wfolarry]

I'll have to look for it but I'll find it for you.

[1FSTRK]

I'll have to look for it but I'll find it for you.

Thank you
I have information on it but I do not see how it would apply at street compression, rpm, and cam timings. Anything on engines in the common street Harley parameters would be great.

[Don D]

Eric
You will find a full discussion of exhaust valve sizes and the relationship of CR on the exhaust opening point on page 71 of David Vizards book How to Build Horsepower isbn 978-1-934709-17-7.

[1FSTRK]

Eric
You will find a full discussion of exhaust valve sizes and the relationship of CR on the exhaust opening point on page 71 of David Vizards book How to Build Horsepower isbn 978-1-934709-17-7.

I have that book somewhere.
I will re-read that section to see how it may apply here.

[1FSTRK]

Eric
You will find a full discussion of exhaust valve sizes and the relationship of CR on the exhaust opening point on page 71 of David Vizards book How to Build Horsepower isbn 978-1-934709-17-7.

I have that book somewhere.
I will re-read that section to see how it may apply here.

I found my copy of David's book and looked through what you referenced.

Many members don't have a copy and just like at the book club you have to have read the book to join the discussion so I will try to be brief.

The chart and paragraphs compare a theoretical 2:1 compression engine to a 15:1 compression engine to over exaggerate the point he is trying to make.  Because it would take referencing a chart not everyone can see and then crunching numbers and being very specific throughout an on point discussion here on an open forum I will not start down that rabbit hole with you.

I will simply say IMHO if you are referencing that material in this discussion it is like someone having a Softail bagger with SE255 cams and they want a little more power at 5000rpm so you I tell them all about the importance of valve train weight and geometry and use a 8 second 8000 rpm drag motor as an example to make your My point and then sell him a complete Jessel valve train set up for his SE 255 cam touring Softail. Everything you I told him about the Jessel valve train was true but his engine will not have any meaningful gains in the area he requested from the technology, in this case all that truth has been misapplied.

This post has been sanitized for political correctness.

[wfolarry]

I'll give you an example of a recent build
A local shop I do work for wanted to squeeze a little more HP out of their standard build they do for customers [107, S&S 585]. They didn't want to change any of the parts [bigger valves etc] just wanted to get a few more HP out of it so he would have bragging rights over his friends who already had their bikes built. All I did was punch out the throat on the exhaust. It gave him more HP but it gave up the low end torque as well. When they asked me why I told them 'you wanted more HP. You got more HP. You didn't want to change anything else'. Changing just one thing changes everything.

[Admiral Akbar]

1.7 rockers & even exhaust valve size are tuning aids in different applications.
Example 1: Low compression. These motors like a later opening exhaust valve because they are building pressure longer so you want to get the most out of it. Now lets bump the compression up with the same cam. Since we can't open it sooner [same cam] going with the 1.7's will open it faster. With a little luck [no way of knowing for sure without testing] we'll make more power. If we go with the 1.7's at the same compression we'll lose power because we lose pressure in the cylinder faster.
Example 2: High compression. Here we want to open the exhaust valve sooner because the pressure in the cylinder is decaying at a faster rate. So with the right cam everything is fine. Putting a 1.7 here will do nothing. Will a bigger exhaust valve help? Maybe. Sometimes bigger valves with the same size throat will flow better because of the chamber shape. So what works in one head doesn't necessarily mean it will work in another. I like to use the smallest chambers possible but that's just me. You'll get arguments that go both ways on that.
The reason why you hear that increasing the ratio on the intake always helps because many believe you can't open the intake fast enough.
On the intake side the pushrod has a straighter shot so you can get away with it. On the exhaust side I think you're pushing your luck.
As far as exhaust lift goes. You don't need as much lift on the exhaust side because by the main event is over sooner but using a lower lift also means you should be using a different spring. Opening it to the same lift means you're just opening into dead space which doesn't hurt anything but you're using the same springs on both sides now. Easier.
As always it's all about the combination of parts. Some make more power than others because everything is complimenting each other. Same as the members here. 
JMO. Maybe I'm wrong. Don't just tell me I'm wrong. Prove it. I like having discussions. 

While the ideas examples of whats happening when the exhaust valve opens are interesting, I'm not sure they have all that much effect.. The simulators indicate that the cylinder pressure is only about 80-90 psi at valve open.. With the piston at the last 40-60 degrees to the bottom of the stroke, the mechanical advantage of the crank is diminished and with the rocker ratios changing valve timing one only a degree or 2, the difference in generated TQ is negligible..

I think that the more important event for the exhaust is exhaust close and what flow is doing in the pipe.  Too much exhaust duration and the flow either reverses or stops..  The 635 cam is interesting because the exhaust valve closes way late.. Way more than anything that it out there.. I suspect that to optimize this later close, the exhaust port / systems needs to be stepped and small to keep exhaust flow from reversing... 

I suspect that the reason why higher ratio rockers don't do much on the exhaust is that once there is enough exhaust flow, a little more won't do much. On the intake side, it is harder to fill the cylinder in most cases. The little extra lift on the intake helps when flow is needed.. When a builder finally gets a set of heads that are more than adequate on the intake, higher ratio rockers aren't needed.

[wfolarry]

1.7 rockers & even exhaust valve size are tuning aids in different applications.
Example 1: Low compression. These motors like a later opening exhaust valve because they are building pressure longer so you want to get the most out of it. Now lets bump the compression up with the same cam. Since we can't open it sooner [same cam] going with the 1.7's will open it faster. With a little luck [no way of knowing for sure without testing] we'll make more power. If we go with the 1.7's at the same compression we'll lose power because we lose pressure in the cylinder faster.
Example 2: High compression. Here we want to open the exhaust valve sooner because the pressure in the cylinder is decaying at a faster rate. So with the right cam everything is fine. Putting a 1.7 here will do nothing. Will a bigger exhaust valve help? Maybe. Sometimes bigger valves with the same size throat will flow better because of the chamber shape. So what works in one head doesn't necessarily mean it will work in another. I like to use the smallest chambers possible but that's just me. You'll get arguments that go both ways on that.
The reason why you hear that increasing the ratio on the intake always helps because many believe you can't open the intake fast enough.
On the intake side the pushrod has a straighter shot so you can get away with it. On the exhaust side I think you're pushing your luck.
As far as exhaust lift goes. You don't need as much lift on the exhaust side because by the main event is over sooner but using a lower lift also means you should be using a different spring. Opening it to the same lift means you're just opening into dead space which doesn't hurt anything but you're using the same springs on both sides now. Easier.
As always it's all about the combination of parts. Some make more power than others because everything is complimenting each other. Same as the members here. 
JMO. Maybe I'm wrong. Don't just tell me I'm wrong. Prove it. I like having discussions. 

While the ideas examples of whats happening when the exhaust valve opens are interesting, I'm not sure they have all that much effect.. The simulators indicate that the cylinder pressure is only about 80-90 psi at valve open.. With the piston at the last 40-60 degrees to the bottom of the stroke, the mechanical advantage of the crank is diminished and with the rocker ratios changing valve timing one only a degree or 2, the difference in generated TQ is negligible..

I think that the more important event for the exhaust is exhaust close and what flow is doing in the pipe.  Too much exhaust duration and the flow either reverses or stops..  The 635 cam is interesting because the exhaust valve closes way late.. Way more than anything that it out there.. I suspect that to optimize this later close, the exhaust port / systems needs to be stepped and small to keep exhaust flow from reversing... 

I suspect that the reason why higher ratio rockers don't do much on the exhaust is that once there is enough exhaust flow, a little more won't do much. On the intake side, it is harder to fill the cylinder in most cases. The little extra lift on the intake helps when flow is needed.. When a builder finally gets a set of heads that are more than adequate on the intake, higher ratio rockers aren't needed.

Timing of the exhaust opening is important to get all the power out of the combustion event while still maintaining enough energy to get it moving out of the chamber & into the pipe. Open it too late & the piston is doing too much work pushing it out the pipe.

[Admiral Akbar]

1.7 rockers & even exhaust valve size are tuning aids in different applications.
Example 1: Low compression. These motors like a later opening exhaust valve because they are building pressure longer so you want to get the most out of it. Now lets bump the compression up with the same cam. Since we can't open it sooner [same cam] going with the 1.7's will open it faster. With a little luck [no way of knowing for sure without testing] we'll make more power. If we go with the 1.7's at the same compression we'll lose power because we lose pressure in the cylinder faster.
Example 2: High compression. Here we want to open the exhaust valve sooner because the pressure in the cylinder is decaying at a faster rate. So with the right cam everything is fine. Putting a 1.7 here will do nothing. Will a bigger exhaust valve help? Maybe. Sometimes bigger valves with the same size throat will flow better because of the chamber shape. So what works in one head doesn't necessarily mean it will work in another. I like to use the smallest chambers possible but that's just me. You'll get arguments that go both ways on that.
The reason why you hear that increasing the ratio on the intake always helps because many believe you can't open the intake fast enough.
On the intake side the pushrod has a straighter shot so you can get away with it. On the exhaust side I think you're pushing your luck.
As far as exhaust lift goes. You don't need as much lift on the exhaust side because by the main event is over sooner but using a lower lift also means you should be using a different spring. Opening it to the same lift means you're just opening into dead space which doesn't hurt anything but you're using the same springs on both sides now. Easier.
As always it's all about the combination of parts. Some make more power than others because everything is complimenting each other. Same as the members here. 
JMO. Maybe I'm wrong. Don't just tell me I'm wrong. Prove it. I like having discussions. 

While the ideas examples of whats happening when the exhaust valve opens are interesting, I'm not sure they have all that much effect.. The simulators indicate that the cylinder pressure is only about 80-90 psi at valve open.. With the piston at the last 40-60 degrees to the bottom of the stroke, the mechanical advantage of the crank is diminished and with the rocker ratios changing valve timing one only a degree or 2, the difference in generated TQ is negligible..

I think that the more important event for the exhaust is exhaust close and what flow is doing in the pipe.  Too much exhaust duration and the flow either reverses or stops..  The 635 cam is interesting because the exhaust valve closes way late.. Way more than anything that it out there.. I suspect that to optimize this later close, the exhaust port / systems needs to be stepped and small to keep exhaust flow from reversing... 

I suspect that the reason why higher ratio rockers don't do much on the exhaust is that once there is enough exhaust flow, a little more won't do much. On the intake side, it is harder to fill the cylinder in most cases. The little extra lift on the intake helps when flow is needed.. When a builder finally gets a set of heads that are more than adequate on the intake, higher ratio rockers aren't needed.

Timing of the exhaust opening is important to get all the power out of the combustion event while still maintaining enough energy to get it moving out of the chamber & into the pipe. Open it too late & the piston is doing too much work pushing it out the pipe.

This brings up the reason why exhaust open is less important.. It's part of the cycle where delaying the exhaust open to make more power (tq) also wastes power due to higher pumping losses.. Not sure of what the magnitude of the 2 will be but for sure it depends on exhaust port / exhaust system flow.  If the magnitudes are close, changing the exhaust open event does nothing unless it effects what is happening during overlap.. 

[PanHeadRed]

it is like someone having a Softail bagger with SE255 cams and they want a little more power at 5000rpm so someone tell them all about....... a 8 second 8000 rpm drag motor as an example to make their point

Welcome to the forum.

[PanHeadRed]

I'll give you an example of a recent build
A local shop I do work for wanted to squeeze a little more HP out of their standard build they do for customers [107, S&S 585]. They didn't want to change any of the parts [bigger valves etc] just wanted to get a few more HP out of it so he would have bragging rights over his friends who already had their bikes built. All I did was punch out the throat on the exhaust. It gave him more HP but it gave up the low end torque as well. When they asked me why I told them 'you wanted more HP. You got more HP. You didn't want to change anything else'. Changing just one thing changes everything.

After the ex mod it's possible he could have used a shorter cam and had the top HP gain and kept the low rpm power as well.

[Don D]

Eric
You will find a full discussion of exhaust valve sizes and the relationship of CR on the exhaust opening point on page 71 of David Vizards book How to Build Horsepower isbn 978-1-934709-17-7.

I have that book somewhere.
I will re-read that section to see how it may apply here.

I found my copy of David's book and looked through what you referenced.

Many members don't have a copy and just like at the book club you have to have read the book to join the discussion so I will try to be brief.

The chart and paragraphs compare a theoretical 2:1 compression engine to a 15:1 compression engine to over exaggerate the point he is trying to make.  Because it would take referencing a chart not everyone can see and then crunching numbers and being very specific throughout an on point discussion here on an open forum I will not start down that rabbit hole with you.

I will simply say IMHO if you are referencing that material in this discussion it is like someone having a Softail bagger with SE255 cams and they want a little more power at 5000rpm so you tell them all about the importance of valve train weight and geometry and use a 8 second 8000 rpm drag motor as an example to make your point and then sell him a complete Jessel valve train set up for his SE 255 cam touring Softail. Everything you told him about the Jessel valve train was true but his engine will not have any meaningful gains in the area he requested from the technology, in his case all that truth has been misapplied.

You see, there is no rabbit hole. That is your mirage. I simply post a book with a good explanation of the relationship Larry was describing, quite well I might add, and you twist this into me being bad for referencing something everybody may not have. I could scan the page?? Just the messenger ya know..

"I will simply say IMHO if you are referencing that material in this discussion it is like someone having a Softail bagger with SE255 cams and they want a little more power at 5000rpm so you tell them all about the importance of valve train weight and geometry and use a 8 second 8000 rpm drag motor as an example to make your point and then sell him a complete Jessel valve train"

Clever..
Yet another example of taking an informative discussion off course with BS trying to discount, discredit and vilify me.
Vizard clearly is showing how the compression ratio influences valve sizing ratio and the criticality of the cams opening point on the exhaust side as this relates to the compression ratio. This is exactly what you wanted and asked Larry about. Vizards example is extreme to make a point, but I am sure you knew that.
I did scan it for the benefit of others to read and decide for themselves.

Larrys example is real world and works. And yet another example of no free lunch.

Bottom line..
A larger rocker ratio is a tuning aid. Hopefully a camshaft that is reasonably close to matching the goals of the build is already in the motor. Changing rocker ratios is a method to perhaps extract a small amount more torque and horsepower and may also alter the torque curve in the process for good or bad. It is up to the individual if they want to go to the time trouble and expense to do something that may provide a small or no gain. The exhaust side, IMHO, adding rocker ratio could have more of a potential downside because higher lift occurs during a point in the IC process that does not need it and the small benefit that may occur would be a faster and slightly earlier exhaust opening during blowdown assuming the exhaust lobe is not already pushing mechanical limits.

This topic is covered and then some. There are many good responses and the OP certainly has an answer to his question.

[Removed CR material]

[kd]

1.7 rockers & even exhaust valve size are tuning aids in different applications.
Example 1: Low compression. These motors like a later opening exhaust valve because they are building pressure longer so you want to get the most out of it. Now lets bump the compression up with the same cam. Since we can't open it sooner [same cam] going with the 1.7's will open it faster. With a little luck [no way of knowing for sure without testing] we'll make more power. If we go with the 1.7's at the same compression we'll lose power because we lose pressure in the cylinder faster.
Example 2: High compression. Here we want to open the exhaust valve sooner because the pressure in the cylinder is decaying at a faster rate. So with the right cam everything is fine. Putting a 1.7 here will do nothing. Will a bigger exhaust valve help? Maybe. Sometimes bigger valves with the same size throat will flow better because of the chamber shape. So what works in one head doesn't necessarily mean it will work in another. I like to use the smallest chambers possible but that's just me. You'll get arguments that go both ways on that.
The reason why you hear that increasing the ratio on the intake always helps because many believe you can't open the intake fast enough.
On the intake side the pushrod has a straighter shot so you can get away with it. On the exhaust side I think you're pushing your luck.
As far as exhaust lift goes. You don't need as much lift on the exhaust side because by the main event is over sooner but using a lower lift also means you should be using a different spring. Opening it to the same lift means you're just opening into dead space which doesn't hurt anything but you're using the same springs on both sides now. Easier.
As always it's all about the combination of parts. Some make more power than others because everything is complimenting each other. Same as the members here. 
JMO. Maybe I'm wrong. Don't just tell me I'm wrong. Prove it. I like having discussions. 

While the ideas examples of whats happening when the exhaust valve opens are interesting, I'm not sure they have all that much effect.. The simulators indicate that the cylinder pressure is only about 80-90 psi at valve open.. With the piston at the last 40-60 degrees to the bottom of the stroke, the mechanical advantage of the crank is diminished and with the rocker ratios changing valve timing one only a degree or 2, the difference in generated TQ is negligible..

I think that the more important event for the exhaust is exhaust close and what flow is doing in the pipe.  Too much exhaust duration and the flow either reverses or stops..  The 635 cam is interesting because the exhaust valve closes way late.. Way more than anything that it out there.. I suspect that to optimize this later close, the exhaust port / systems needs to be stepped and small to keep exhaust flow from reversing... 

I suspect that the reason why higher ratio rockers don't do much on the exhaust is that once there is enough exhaust flow, a little more won't do much. On the intake side, it is harder to fill the cylinder in most cases. The little extra lift on the intake helps when flow is needed.. When a builder finally gets a set of heads that are more than adequate on the intake, higher ratio rockers aren't needed.

Timing of the exhaust opening is important to get all the power out of the combustion event while still maintaining enough energy to get it moving out of the chamber & into the pipe. Open it too late & the piston is doing too much work pushing it out the pipe.

This brings up the reason why exhaust open is less important.. It's part of the cycle where delaying the exhaust open to make more power (tq) also wastes power due to higher pumping losses.. Not sure of what the magnitude of the 2 will be but for sure it depends on exhaust port / exhaust system flow.  If the magnitudes are close, changing the exhaust open event does nothing unless it effects what is happening during overlap.. 

Let's see if I am keeping up.  One quick question.

When we talk about pumping loss, how does the mechanical advantage of the ex valve opening at the bottom of the swing of the crank figure in? If the valve is sized properly and the seat radius is effective, the flow should start at this point without too much pumping loss. If the simulator is correct and the pressure remaining is 80 -90 # then the initial bleed-off should drop that residual to a level the pumping loss is depreciated.   Once the gasses are in motion, the exhaust port design and the exhaust system should be a larger influence. Am I there yet?   

[wfolarry]

I'll give you an example of a recent build
A local shop I do work for wanted to squeeze a little more HP out of their standard build they do for customers [107, S&S 585]. They didn't want to change any of the parts [bigger valves etc] just wanted to get a few more HP out of it so he would have bragging rights over his friends who already had their bikes built. All I did was punch out the throat on the exhaust. It gave him more HP but it gave up the low end torque as well. When they asked me why I told them 'you wanted more HP. You got more HP. You didn't want to change anything else'. Changing just one thing changes everything.

After the ex mod it's possible he could have used a shorter cam and had the top HP gain and kept the low rpm power as well.

Maybe but that's not what he wanted & I thought I made that clear. Same parts.

[wfolarry]

1.7 rockers & even exhaust valve size are tuning aids in different applications.
Example 1: Low compression. These motors like a later opening exhaust valve because they are building pressure longer so you want to get the most out of it. Now lets bump the compression up with the same cam. Since we can't open it sooner [same cam] going with the 1.7's will open it faster. With a little luck [no way of knowing for sure without testing] we'll make more power. If we go with the 1.7's at the same compression we'll lose power because we lose pressure in the cylinder faster.
Example 2: High compression. Here we want to open the exhaust valve sooner because the pressure in the cylinder is decaying at a faster rate. So with the right cam everything is fine. Putting a 1.7 here will do nothing. Will a bigger exhaust valve help? Maybe. Sometimes bigger valves with the same size throat will flow better because of the chamber shape. So what works in one head doesn't necessarily mean it will work in another. I like to use the smallest chambers possible but that's just me. You'll get arguments that go both ways on that.
The reason why you hear that increasing the ratio on the intake always helps because many believe you can't open the intake fast enough.
On the intake side the pushrod has a straighter shot so you can get away with it. On the exhaust side I think you're pushing your luck.
As far as exhaust lift goes. You don't need as much lift on the exhaust side because by the main event is over sooner but using a lower lift also means you should be using a different spring. Opening it to the same lift means you're just opening into dead space which doesn't hurt anything but you're using the same springs on both sides now. Easier.
As always it's all about the combination of parts. Some make more power than others because everything is complimenting each other. Same as the members here. 
JMO. Maybe I'm wrong. Don't just tell me I'm wrong. Prove it. I like having discussions. 

While the ideas examples of whats happening when the exhaust valve opens are interesting, I'm not sure they have all that much effect.. The simulators indicate that the cylinder pressure is only about 80-90 psi at valve open.. With the piston at the last 40-60 degrees to the bottom of the stroke, the mechanical advantage of the crank is diminished and with the rocker ratios changing valve timing one only a degree or 2, the difference in generated TQ is negligible..

I think that the more important event for the exhaust is exhaust close and what flow is doing in the pipe.  Too much exhaust duration and the flow either reverses or stops..  The 635 cam is interesting because the exhaust valve closes way late.. Way more than anything that it out there.. I suspect that to optimize this later close, the exhaust port / systems needs to be stepped and small to keep exhaust flow from reversing... 

I suspect that the reason why higher ratio rockers don't do much on the exhaust is that once there is enough exhaust flow, a little more won't do much. On the intake side, it is harder to fill the cylinder in most cases. The little extra lift on the intake helps when flow is needed.. When a builder finally gets a set of heads that are more than adequate on the intake, higher ratio rockers aren't needed.

Timing of the exhaust opening is important to get all the power out of the combustion event while still maintaining enough energy to get it moving out of the chamber & into the pipe. Open it too late & the piston is doing too much work pushing it out the pipe.

This brings up the reason why exhaust open is less important.. It's part of the cycle where delaying the exhaust open to make more power (tq) also wastes power due to higher pumping losses.. Not sure of what the magnitude of the 2 will be but for sure it depends on exhaust port / exhaust system flow.  If the magnitudes are close, changing the exhaust open event does nothing unless it effects what is happening during overlap..

Aren't you the same guy that says the S&S 570 cam is over exhausting?

[wfolarry]

1.7 rockers & even exhaust valve size are tuning aids in different applications.
Example 1: Low compression. These motors like a later opening exhaust valve because they are building pressure longer so you want to get the most out of it. Now lets bump the compression up with the same cam. Since we can't open it sooner [same cam] going with the 1.7's will open it faster. With a little luck [no way of knowing for sure without testing] we'll make more power. If we go with the 1.7's at the same compression we'll lose power because we lose pressure in the cylinder faster.
Example 2: High compression. Here we want to open the exhaust valve sooner because the pressure in the cylinder is decaying at a faster rate. So with the right cam everything is fine. Putting a 1.7 here will do nothing. Will a bigger exhaust valve help? Maybe. Sometimes bigger valves with the same size throat will flow better because of the chamber shape. So what works in one head doesn't necessarily mean it will work in another. I like to use the smallest chambers possible but that's just me. You'll get arguments that go both ways on that.
The reason why you hear that increasing the ratio on the intake always helps because many believe you can't open the intake fast enough.
On the intake side the pushrod has a straighter shot so you can get away with it. On the exhaust side I think you're pushing your luck.
As far as exhaust lift goes. You don't need as much lift on the exhaust side because by the main event is over sooner but using a lower lift also means you should be using a different spring. Opening it to the same lift means you're just opening into dead space which doesn't hurt anything but you're using the same springs on both sides now. Easier.
As always it's all about the combination of parts. Some make more power than others because everything is complimenting each other. Same as the members here. 
JMO. Maybe I'm wrong. Don't just tell me I'm wrong. Prove it. I like having discussions. 

While the ideas examples of whats happening when the exhaust valve opens are interesting, I'm not sure they have all that much effect.. The simulators indicate that the cylinder pressure is only about 80-90 psi at valve open.. With the piston at the last 40-60 degrees to the bottom of the stroke, the mechanical advantage of the crank is diminished and with the rocker ratios changing valve timing one only a degree or 2, the difference in generated TQ is negligible..

I think that the more important event for the exhaust is exhaust close and what flow is doing in the pipe.  Too much exhaust duration and the flow either reverses or stops..  The 635 cam is interesting because the exhaust valve closes way late.. Way more than anything that it out there.. I suspect that to optimize this later close, the exhaust port / systems needs to be stepped and small to keep exhaust flow from reversing... 

I suspect that the reason why higher ratio rockers don't do much on the exhaust is that once there is enough exhaust flow, a little more won't do much. On the intake side, it is harder to fill the cylinder in most cases. The little extra lift on the intake helps when flow is needed.. When a builder finally gets a set of heads that are more than adequate on the intake, higher ratio rockers aren't needed.

Timing of the exhaust opening is important to get all the power out of the combustion event while still maintaining enough energy to get it moving out of the chamber & into the pipe. Open it too late & the piston is doing too much work pushing it out the pipe.

This brings up the reason why exhaust open is less important.. It's part of the cycle where delaying the exhaust open to make more power (tq) also wastes power due to higher pumping losses.. Not sure of what the magnitude of the 2 will be but for sure it depends on exhaust port / exhaust system flow.  If the magnitudes are close, changing the exhaust open event does nothing unless it effects what is happening during overlap.. 

Let's see if I am keeping up.  One quick question.

When we talk about pumping loss, how does the mechanical advantage of the ex valve opening at the bottom of the swing of the crank figure in? If the valve is sized properly and the seat radius is effective, the flow should start at this point without too much pumping loss. If the simulator is correct and the pressure remaining is 80 -90 # then the initial bleed-off should drop that residual to a level the pumping loss is depreciated.   Once the gasses are in motion, the exhaust port design and the exhaust system should be a larger influence. Am I there yet?   

When the piston gets to BDC you want all the exhaust out so that when it starts going up it has less work to do. If you had to push everything out you would lose power. That's why ex opening is important.

[Admiral Akbar]

Aren't you the same guy that says the S&S 570 cam is over exhausting?

That be me... 

[Admiral Akbar]

Let's see if I am keeping up.  One quick question.

When we talk about pumping loss, how does the mechanical advantage of the ex valve opening at the bottom of the swing of the crank figure in? If the valve is sized properly and the seat radius is effective, the flow should start at this point without too much pumping loss. If the simulator is correct and the pressure remaining is 80 -90 # then the initial bleed-off should drop that residual to a level the pumping loss is depreciated.   Once the gasses are in motion, the exhaust port design and the exhaust system should be a larger influence. Am I there yet?   

With the piston still going down there is no pumping loss. There is TQ loss as pressure in the cylinder drops quickly.. The less pumping loss is on the exhaust stroke.. With an early open, there is less in the cylinder to push out so the motor has less work to do.    Of course the exhaust system flow, effects pumping loss..

[Admiral Akbar]

Eric
You will find a full discussion of exhaust valve sizes and the relationship of CR on the exhaust opening point on page 71 of David Vizards book How to Build Horsepower isbn 978-1-934709-17-7.

I have that book somewhere.
I will re-read that section to see how it may apply here.

I found my copy of David's book and looked through what you referenced.

Many members don't have a copy and just like at the book club you have to have read the book to join the discussion so I will try to be brief.

The chart and paragraphs compare a theoretical 2:1 compression engine to a 15:1 compression engine to over exaggerate the point he is trying to make.  Because it would take referencing a chart not everyone can see and then crunching numbers and being very specific throughout an on point discussion here on an open forum I will not start down that rabbit hole with you.

I will simply say IMHO if you are referencing that material in this discussion it is like someone having a Softail bagger with SE255 cams and they want a little more power at 5000rpm so you tell them all about the importance of valve train weight and geometry and use a 8 second 8000 rpm drag motor as an example to make your point and then sell him a complete Jessel valve train set up for his SE 255 cam touring Softail. Everything you told him about the Jessel valve train was true but his engine will not have any meaningful gains in the area he requested from the technology, in his case all that truth has been misapplied.

You see, there is no rabbit hole. That is your mirage. I simply post a book with a good explanation of the relationship Larry was describing, quite well I might add, and you twist this into me being bad for referencing something everybody may not have. I could scan the page?? Just the messenger ya know..

"I will simply say IMHO if you are referencing that material in this discussion it is like someone having a Softail bagger with SE255 cams and they want a little more power at 5000rpm so you tell them all about the importance of valve train weight and geometry and use a 8 second 8000 rpm drag motor as an example to make your point and then sell him a complete Jessel valve train"

Clever..
Yet another example of taking an informative discussion off course with BS trying to discount, discredit and vilify me.
Vizard clearly is showing how the compression ratio influences valve sizing ratio and the criticality of the cams opening point on the exhaust side as this relates to the compression ratio. This is exactly what you wanted and asked Larry about. Vizards example is extreme to make a point, but I am sure you knew that.
I did scan it for the benefit of others to read and decide for themselves.

Larrys example is real world and works. And yet another example of no free lunch.

Bottom line..
A larger rocker ratio is a tuning aid. Hopefully a camshaft that is reasonably close to matching the goals of the build is already in the motor. Changing rocker ratios is a method to perhaps extract a small amount more torque and horsepower and may also alter the torque curve in the process for good or bad. It is up to the individual if they want to go to the time trouble and expense to do something that may provide a small or no gain. The exhaust side, IMHO, adding rocker ratio could have more of a potential downside because higher lift occurs during a point in the IC process that does not need it and the small benefit that may occur would be a faster and slightly earlier exhaust opening during blowdown assuming the exhaust lobe is not already pushing mechanical limits.

This topic is covered and then some. There are many good responses and the OP certainly has an answer to his question.

While you 2 guys want to butt heads over this, you really need to look at the context of what Vizard is doing.. He is only giving an example of how CR ratio effects the pressure / volume curve on the power stroke.. A motor with 2 to 1 CR won't ever come close to generating the TQ of a 15 to one motor even tho he says the exhaust needs to be held closed longer.. He's using exhaust close as a bad example IMO..

[1FSTRK]

I agree but beyond that the effects even in his chart show that at the street level you could make more difference in output with almost any other component change and that was the point of my over exaggerated example.

I fixed my post to try and make it more politically correct.
Don you need to ease up buddy your going to have a stroke.

[Admiral Akbar]

While Vizzard does go a little "Donney" on exhaust valve timing, his overall discussion is very good.  He talks about setting intake to exhaust ratios based on built compression ratios.. Lower compression motors favor higher exhaust valve percentages than higher compression motors. Good for me to see that in print as I've known for some time that lower compression motors need better exhaust flow to perform well but hadn't thought about intake to exhaust ratios. It's less of an issue with higher compression motors. That means you can take advantage leaving the exhaust valve size alone to increase the intake..

[Cracked Head]

Vizards whole point was in describing the expansion ratio to compression ratio properties.The rest is up to the indivduals use of the properties in valve timing events.

[wfolarry]

Here's another example of valve size/shape
Customer brings in a set of heads that have the Kibblewhite exhaust valves [44* back angle I believe]. Heads were done by another shop that does good work so I'm not looking to bash anyone here. They like that valve but in this instance I felt it was the wrong one. Heads flowed good so I just freshened them up with a valve job, seals & different exhaust valves. Back on the dyno it gained 12 HP. Nothing else changed. Opinions?

[Admiral Akbar]

Not enough information..

[PanHeadRed]

I'll give you an example of a recent build
A local shop I do work for wanted to squeeze a little more HP out of their standard build they do for customers [107, S&S 585]. They didn't want to change any of the parts [bigger valves etc] just wanted to get a few more HP out of it so he would have bragging rights over his friends who already had their bikes built. All I did was punch out the throat on the exhaust. It gave him more HP but it gave up the low end torque as well. When they asked me why I told them 'you wanted more HP. You got more HP. You didn't want to change anything else'. Changing just one thing changes everything.

After the ex mod it's possible he could have used a shorter cam and had the top HP gain and kept the low rpm power as well.

Maybe but that's not what he wanted & I thought I made that clear. Same parts.

Clear as a crystal, no challenge at all, just trying to post something to make myself sound smart.

[wfolarry]

Not enough information..

It was a 117, Wood cam [don't remember which one], 2" intake on stock heads. That's about all I remember.

[PanHeadRed]

different exhaust valves.

I'm listening, constantly learning.

[harleytuner]

Not enough information..

It was a 117, Wood cam [don't remember which one], 2" intake on stock heads. That's about all I remember.

Same dyno? Similar run conditions?

[wfolarry]

Yes & Yes.

[harleytuner]

Yes & Yes.

interesting.  Just a valve job and new (different valves)?  Same HG?

[wfolarry]

Yes.

[1FSTRK]

For those looking at the Vizard pressure chart he makes the statement that the red line and the light-blue line represent the starting and finishing pressures of the 15:1 and 2:1 on the same scale. Given that the bottom axis is only labeled TDC on the left and BDC on the right, I draw the conclusion that 90 degrees BBDC is the center of the chart, We then can clearly see that by about 60 degrees BBDC the two lines touch and the pressure is equal for the 15:1 and 2:1 engines. Given that very few HD street cams have an exhaust valve opening of earlier than 60 degrees and many of the popular ones are in the 40 and 50 degree range they would all open at the same cylinder pressure in both compression examples Dave uses. Now to our previous examples from Larry's post quoted below, see if anything in Larry's example engines has us working in the ranges of Dave's chart where there are actually pressure differences. I do not see where Larry's changes put anything in the area of Dave's chart where the pressures are different so if it does not show difference on the 15:1 compared to 2:1 pressure chart what kind of cylinder pressure difference will be seen with motors ranging from 10:1 to 11:1. While technically correct just like in my Softail example, not applicable to a street HD with a rocker ratio change. It is just my take on this after seeing many dyno tests involving race engines where these principals did apply.

My point has been that many solid principals and theories for high rpm, high compression, narrow tq band race engines either have little effect or adverse effect on street Harleys.

1.7 rockers & even exhaust valve size are tuning aids in different applications.
Example 1: Low compression. These motors like a later opening exhaust valve because they are building pressure longer so you want to get the most out of it. Now lets bump the compression up with the same cam. Since we can't open it sooner [same cam] going with the 1.7's will open it faster. With a little luck [no way of knowing for sure without testing] we'll make more power. If we go with the 1.7's at the same compression we'll lose power because we lose pressure in the cylinder faster.
Example 2: High compression. Here we want to open the exhaust valve sooner because the pressure in the cylinder is decaying at a faster rate. So with the right cam everything is fine. Putting a 1.7 here will do nothing. Will a bigger exhaust valve help? Maybe. Sometimes bigger valves with the same size throat will flow better because of the chamber shape. So what works in one head doesn't necessarily mean it will work in another. I like to use the smallest chambers possible but that's just me. You'll get arguments that go both ways on that.
The reason why you hear that increasing the ratio on the intake always helps because many believe you can't open the intake fast enough.
On the intake side the pushrod has a straighter shot so you can get away with it. On the exhaust side I think you're pushing your luck.
As far as exhaust lift goes. You don't need as much lift on the exhaust side because by the main event is over sooner but using a lower lift also means you should be using a different spring. Opening it to the same lift means you're just opening into dead space which doesn't hurt anything but you're using the same springs on both sides now. Easier.
As always it's all about the combination of parts. Some make more power than others because everything is complimenting each other. Same as the members here. 
JMO. Maybe I'm wrong. Don't just tell me I'm wrong. Prove it. I like having discussions. 

[Admiral Akbar]

Not enough information..

It was a 117, Wood cam [don't remember which one], 2" intake on stock heads. That's about all I remember.

And the flow was the same between these 2 valves? 

[attach=0]

Average Flow?

[wfolarry]

The low lift #'s were better with the replacement valve.

[Admiral Akbar]

The low lift #'s were better with the replacement valve.

OK so the motor liked more flow at low lifts.. It would be interesting to look at all the details, pipe used, cam, head flow, TB and where the HP differed.  First item would be flow area under the curve between the 2 head versions...

[wfolarry]

Why is it that guys will spend hours tuning their bikes going over every cell, fuel, timing & anything else they can adjust on the bike but they don't want to tune the parts that go into the motor?

[Admiral Akbar]

You talkin' them $299 heads again? 

[Don D]

Before everyone ditches Kibblewhite valves it is important to state the geometry is very different in other ways with the AV&V not just the under head angle.
Seat width, margin, top cut. Plus in some ports the Kibblewhite may have worked better just not in Larrys case. One point I remember from conversations with Mike Roland was he emphasized the importance of low lift exhaust flow and also in the same context discounted the value of high lift exhaust flow for reasons I already stated.