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)