Performance difference between High lift cams and Low lift cams

[Tre_11 FLHX]

I am sure this has been asked before, just can't find it.  I was just wondering what the difference in performance was with a high lift and a low lift cam if all the numbers are almost identical except lift.  Example:

TW-6-6
20/40
42/18
240
240
.510
.510
.191
.173
 
TW-7H
20/40
42/18
240
240
.575
.575
.194
.176

[wfolarry]

Higher lift will make the motor think it has a bigger cam at high RPM's while still running good down low. How well your valve train holds up is a different story.

[txtech]

   

[Tre_11 FLHX]

WFOLarry- I was thinking the same thing- I am by far no expert, but when I was talking to Bob W a few weeks back, he could not give me a clear answer, wanted me to go with tw7h, titanium this and that, Jag oil cooler etc. But never gave me a reason to go with the tw7h.

[NightTrain67]

Higher lift equals more airflow available, but that is only part of the story.  With everything else being equal, higher lift will mean quicker opening and closing events.....that equals more valve train wear and tear.  And if your heads can't flow the air at the higher lift numbers, you will not be gaining anything but increased valvetrain abuse. It is just about useless to use a .600 lift cam if your head does not show increasing flow numbers past .500.

[steelknee57]

I don't understand why the high lift cams need more static compression. I have read that the Woods 6 suggested ratio is 10.0 to 1 but the 6h (I don't know about the 7h) is 10.5 to 1. And that the more compression helps the bottom end on the high lift cam.

[NightTrain67]

I don't understand why the high lift cams need more static compression. I have read that the Woods 6 suggested ratio is 10.0 to 1 but the 6h (I don't know about the 7h) is 10.5 to 1. And that the more compression helps the bottom end on the high lift cam.

Lift does not effect compression at all.. Duration, Overlap, Lobe Seperation Angle, and Centerline can dictate what compression the motor will need.

[PanHeadRed]

 > I was just wondering what the difference in performance was.......if all the numbers are almost identical except lift.<

Typically the higher lift produces higher peak #'s.

[Jeffd]

I don't know if this is bs or not but a few years ago Ralph at Andrews told me via a telephone conversation that the higher the lift the lower the mpg.  He said that for best mpg use the lowest lift possible for your particular application. I realize that for many applications mpg is of no concern.

[taz95dog]

suppose it's only a"3/4" racing cam? ..hey dave ,if that's, you merry Christmas if not still merry Christmas.. ..bill...

[NightTrain67]

suppose it's only a"3/4" racing cam? ..hey dave ,if that's, you merry Christmas if not still merry Christmas.. ..bill...

Hey Bill.....It's me.  Merry Christmas to you, as well.

[taz95dog]

 

[wfolarry]

I don't know if this is bs or not but a few years ago Ralph at Andrews told me via a telephone conversation that the higher the lift the lower the mpg.  He said that for best mpg use the lowest lift possible for your particular application. I realize that for many applications mpg is of no concern.

It's B.S.

[Bakon]

More lift= more air/fuel= more power= less mpg not sure= more fun= more money for other parts = more conversation in here

heads and cams and compression are all parts of the receipe which need to match. Higher lift is going to give more flow given the other parts can give it.

[uglyDougly]

  Completely with Larry on the subject.
 At part throttle (where you run when looking for mileage) the MAP controls the air flow and the low pressure makes the fuel condition much better than WOT.

 After that the only thing that matters is the inlet closing and exhaust opening.

 For cams with identical inlet closing and exhaust opening, lift will have no effect on mileage at part throttle.

  These cam discussions seem to get max power (WOT) and economy (part throttle) intertwined and they are definitely different operating regimes.

  The best cam for mileage will make poor HP. But, compression ratio will get you mileage. Finally, tuning will be the last and best place to get fuel economy, so don't forget that variable.

 Doug

[Golfman]

If you have two cams with the same duration and opening and closing events, but one has a much higher lift, it will also likely have a higher contact velocity and quicker opening and closing. The cam will act slightly bigger but the high contact velocity and fast opening rate CAN also increase some torque - a double win as long as it doesn't make it act too big for the combination. The lift itself doesn't help the horsepower once you reach a lift beyond which the head will flow more; but it will help keep the lobe in contact with the lifter. If you had a high opening rate and contact velocity and then just cut the lift at the point where the head doesn't flow anymore the cam lobe would be said to have a high amount of "dwell"; and it would be much harder to keep out of float, without excessive spring pressure, etc.
Another way to accomplish a similar advantage is to use a slightly slower rate cam lobe with a greater rate rocker arm ratio, as the valve rate at any point on the lobe is multiplied by the rocker ratio; and the lifter and pushrod, being before the rocker arm, are not forced to accelerate and decelerate as fast as if all the acceleration was built into the cam lobe.
Golfman
Dave

[PanHeadRed]

>It's B.S.<

Pretty much sums it up.

[Hillside Motorcycle]

As Larry said, you can use the high-lift/short-duration grinds, as long as you use good valve train components.
"Prior proper planning, prevents piss-poor procedure."

[skyhook]

can't believe no one's brought out the "it's only at max lift once, but on the ramps twice" argument!?

[wfolarry]

can't believe no one's brought out the "it's only at max lift once, but on the ramps twice" argument!?

That's B.S. too.

[Jeffd]

I don't know if this is bs or not but a few years ago Ralph at Andrews told me via a telephone conversation that the higher the lift the lower the mpg.  He said that for best mpg use the lowest lift possible for your particular application. I realize that for many applications mpg is of no concern.

It's B.S.

Maybe that is why Ralph apparently is not there any longer LOL.  I do remember at the time I thought it was pretty cool to call to ask a tech question and talk to Ralph.

[KingofCubes]

What happens when you use more lift on a smaller engine with the SE big valve heads?

[loc]

So if you bolt in a TW5-6(.575) lift in say an 08 bike, it will just give you more valve train wear and noise than say the TW6-6 with no performance gains?

[ejk_dyna]

<<So if you bolt in a TW5-6(.575) lift in say an 08 bike, it will just give you more valve train wear and noise than say the TW6-6 with no performance gains?>>

well the 5-6 and 6-6 are 2 different cams so that is not a good comparison.

but the 6-6 and 7H are exactly the same timing with the H 575 lift vs 6-6 510lift

the higher lift cam will be typically be more noisy..in woods case it will be.  how much depends on tolerance stack-ups of valve train and adjustment.

the higher lift has a small benefit at lower rpms as the valve opens more quickly.  not enough to justify the add'l work, noise, wear.

the further above .510 lift your head flows before stalling the greater the performance benefit will be with the 7H

wear factor again depends on parts stack-up and adjustment...but the 7H will definitely reduce overall valve train life.  but in most cases i am not sure it is a practical concern.  like reducing vt life from 200,000 miles to 125,000 miles or something like that.  won't affect most riders.

[Scurvy]

I am mulling over the idea of trying a set of roller rockers at 1.70 ratio on my intakes; Dan Baisley will modify a set of stock ones for $242.
Expensive experiment... (currently at .510 lift with my 37b cams)

[mayor]

I am mulling over the idea of trying a set of roller rockers at 1.70 ratio on my intakes; Dan Baisley will modify a set of stock ones for $242.
Expensive experiment... (currently at .510 lift with my 37b cams)

not going to try and talk you out of that (although, why not just change to a set of 54's with the advance key?), but my guess is your CV40 is holding you back now so you may not see much gains (if your 96" is the same set up you posted on the other site). 

By the way, are you going to post that sheet over here too?  and maybe Jeff can post his 95" tw26build, and then maybe one of you can post the 95" you and Jeff did for your friend.   

[Jeffd]

I am mulling over the idea of trying a set of roller rockers at 1.70 ratio on my intakes; Dan Baisley will modify a set of stock ones for $242.
Expensive experiment... (currently at .510 lift with my 37b cams)

not going to try and talk you out of that (although, why not just change to a set of 54's with the advance key?), but my guess is your CV40 is holding you back now so you may not see much gains (if your 96" is the same set up you posted on the other site). 

By the way, are you going to post that sheet over here too?  and maybe Jeff can post his 95" tw26build, and then maybe one of you can post the 95" you and Jeff did for your friend.   

I have looked high and low and I can not find my dyno graph(s) I am beginning to think they might have gotten shredded with some other documents.  They should still be on the other site if someone knows how to transfer them.

[KingofCubes]

I am mulling over the idea of trying a set of roller rockers at 1.70 ratio on my intakes; Dan Baisley will modify a set of stock ones for $242.
Expensive experiment... (currently at .510 lift with my 37b cams)

You can buy a new set of 1.725 from R&R for that $.

[Don D]

Hold the phone
Is the Wannabe now the Mayor??

[Bakon]

So if you bolt in a TW5-6(.575) lift in say an 08 bike, it will just give you more valve train wear and noise than say the TW6-6 with no performance gains?

Come on, pull the trigger, buy the Tw5-6 already. You know you want it.

[Don D]

EJK sums it up well
The OEM guides are very tough and last a long time when used with OEM or valves of the right material and plating. The noise can be minimized (I thought I would never see the day) by the right lifter preload and not excessive valve spring pressure. In a stock 96" the 5 VS the 6 will produce roughly the same HP and just rev faster and make more torque under the curve. .575 is not excessive lift and there is a huge differance between this .550 to .575 range when comparing to .650. Been there and done that.

[Sonny S.]

Hold the phone
Is the Wannabe now the Mayor??

Obviously I didn't get to vote 

[Deye76]

What happens when you use more lift on a smaller engine with the SE big valve heads?

Torque

[mayor]

Hold the phone
Is the Wannabe now the Mayor??

only in my own mind Don.     that's why the non-capitol "m" in my name.    sadly no mayor position in my little village. 

I just figured sometime's when you fellows called me wannaB it wasn't meant as a compliment (Bruce! ).   

[loc]

Sho,

I do want them but want a quiet valve train and standard valve train wear as well. Its a long winter ahead and  lots of time to decide. Just want to make the right decision.

[KingofCubes]

This is exactly why I prefer the high velocity high cfm cnc ported heads. The energy is so high in the ports that not a lot of lift or rocker geometry work is necessary to gain power. In testing with this type of head, when compairing the lower lift RR525 cam to the higher Andrews 54, it was discovered that the 525 made more torque.

[dadawg]

This is exactly why I prefer the high velocity high cfm cnc ported heads. The energy is so high in the ports that not a lot of lift or rocker geometry work is necessary to gain power. In testing with this type of head, when compairing the lower lift RR525 cam to the higher Andrews 54, it was discovered that the 525 made more torque.

which cam came on earliest?

[sean fxd]

<<In testing with this type of head, when compairing the lower lift RR525 cam to the higher Andrews 54, it was discovered that the 525 made more torque.>>

You have said this several times about the r&r 525.   Since you say it was a TEST that implies back to back work on the dyno.

Each time people have asked to see the dyno sheets.  You say you will get a copy from r&r to post...and it never happens.

Why can't you post the results?

Sean

[Bagger]

Willliam Denish
http://www.hotbikeweb.com/tech/0711_hbkp_tech_tips_camshafts/index.html

Lift is the distance the valve is raised off the seat and is measured in thousandths of an inch. Higher valve lift does not change the engine's power curve. Instead, it generally adds power throughout the entire curve as long as port flow increases at the higher lifts. In general terms, valve lift helps generate torque and horsepower, but the speed at which the valve is raised to full lift is also a factor. Increasing lift is a good way to increase power without significantly reducing low-speed performance. But remember that some cylinder heads stop flowing more air as lift is continually increased. In this situation, a head responds more to duration than lift. From a reliability standpoint, there needs to be some relationship between lift and duration, since only increasing lift without an accompanying increase in duration can produce high valve acceleration rates, which can increase valvetrain wear and reduce reliability. Cams with very high lift and relatively mild duration are typically used to maximize low and midrange power or used with low-compression engines.


FWIW - Additional info:

Lift: Another method of improving cam performance is increasing the amount of lobe lift. Designing a cam profile with more lobe lift results in increased duration in the high-lift regions where cylinder heads flow the most air. Short duration cams with relatively high lift can provide excellent responsiveness, great torque, and good power. But high lift cams are less dependable. You need the right valve springs to handle the increased lift, and the heads must be set up to accommodate the extra lift. There are a few examples where increased lift won't improve performance due to decreased velocity through the port; these typically occur in the race engine world (0.650- to 1.00-inch valve lift). Some late model engines with restrictive throttle-body, intake, cylinder head runner and exhaust flow simply can't flow enough air to support higher lift.

Cam (or lobe) lift is the maximum height or distance that the lifter or follower is raised off the cam. More lift generally means better top-end power, but you’ll sacrifice bottom-end response. In addition, cams with high lift typical put more wear and tear on the valve train.

Sure, with the right cylinder head/piston combination, lifts in the mid 0.500 inch range, even perhaps encroaching on 0.600 inch can work, but pushrods flex, geometry goes AWOL, and the extra benefits of the lift are quashed by the limits of flow through the ports (particularly the exhaust port), so why bother? Mega lift is more valuable to drag racers who re-engineer the whole plot any way.

The other potential problem with increasing the cam lift is that there is only so much clearance between the piston and the valve. The other problem associated with elevated lift numbers is spring fatigue. The greater the lift the farther the spring will have to expand and contract during each rotation of the cam. Cams with more lift are much harder on springs, causing a reduction in spring life.

When comparing cams of the same advertised timing and lifts you would then look at the TDC numbers. For example, the Woods TW6HG has TDC numbers of .192 in .179 ex while the S&S 570 is .187 in and .179 ex although its not a full graph of lobe shape it shows at the same point the woods cam has a more aggressive ramp meaning more lift longer.   This translates into more area under curve to flow and that’s the key which would transfer into more power longer, but also requires heavier spring than the S&S in this case it may be minimal but something to be aware of.

Lift should not necessarily be used to judge how radical a cam is. Increasing valve lift is a function to increase airflow at the valve. Ideally, less lift could be required for maximum output if the cylinder head wasn’t limited by the actual design of it. Increasing engine size compounds this limitation. More lift reduces air speed, for a denser mixture and improved combustion.

[Golfman]

As long as we're getting pretty deep into this, a couple more points:

*This was partly touched on in the last post. The max lift is not what causes piston to valve clearance but generally the lift between 10 degrees BTDC and 10 degrees ATDC. The fast rate cames affect this, as well as where the cam is installed (lobe center or how much advanced or retarded;

* If your sitting there profiling a cam lobe with your degree wheel and dial indicator, remember to use a lifter because, with a roller lifter, the roller becomes part of the profile itself, and increases and decreases lifter acceleration as the contact position of the roller moves from the cam flank to near and over the nose of the cam and back on the closing flank;

* don't NECESSARILY be afraid of more valve spring tension on the seat. All valves with all cams will have some degree of bouncing off the valve seat and it can in effect, if excessive, make the cam seem slightly bigger. If you have the CORRECT size cam it may help to eliminate some of the valve bounce.

[Scurvy]

KoC -thought of that; gotta check to see if they will split up a set (only need 2 intake rockers). Like from S&S I can get a "set", one intake and one exhaust each.
Bagger - execellent info and very helpful. Valve clearance gives me something else to think about.

Mayor... ya man, I wonder if the money would be better spent on a Mikuni than the rockers. I found the old dyno graphs from old HTT and will get them posted.

[mayor]

Scurvy,
thanks for getting them posted.  I think the three charts that you and Jeff posted make great referrence builds for others.  I think spending the money on a carb would make more sense than the rockers with your build.  I'm running the Cv44 with my similar build and love it.

[Scurvy]

mayor - decisions, decisions!  haha... wish I could afford both...

Yeah, I think those dynos and builds make reference builds, especially since your basic 96ft/lbs torque build can be had for under $1000 if one didn't have to pay for shipping.

Do you have an opinion on the CV44 vs. a Mikuni 42 other than the price difference?

[mayor]

[/quote]

Do you have an opinion on the CV44 vs. a Mikuni 42 other than the price difference?

I've ran both, and I still have the Mik sitting on a shelf in the garage but I like the CV44 better.   The Mik42 set up is cheaper since you can still run your factory intake manifold, and the MIk42 on the factory manifold actually outflows the CV44 on the SE manifold.  I just couldn't get the gas milage out of the Mik42. Although, I never set that carb up using afr.  I just used typically recommended jets, and lowered the needle to the lowest position.   The 42 kicks butt in throttle response, but the CV44 set up I have with the lighter DJ spring wakes up pretty fast too.  I'm going to mount the Mik on my sporty, just to make that bike a little more interesting.