1.7 rocker effect

[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 )