cam lift lost

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tblotske

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ok got a question how much lift is lost with a small block mopars valve train geometry say like a cam with 600 lift and what would it end up at the valve
 
the use of 1.6 will increase the total lift at the valve..but the proportional amount of lost will be the same..due to the difference of the plane that the lifters are in and the plane that the valves are in,...

lifters are at 58 degrees...the valves are at 48 degrees....11 degrees difference...take the cosig of 11 degrees x time the lift at the valve...is what i am using...

please provide your explaination.....lol
 
Some time ago I figured something like a 1.52 rocker ratio would be needed to compensate for the lift lost due to geometry. This was for a .474" lift cam. Not sure if there would be a difference for bigger cams. But there are production tolerances, valve heights, etc. that can make a little difference as well.
 
In my stuff I've seen more like a 5% loss with a true 1.5 rocker. .600 lift would hit about .570-.575 range.
 
tblotske said:
ok got a question how much lift is lost with a small block mopars valve train geometry say like a cam with 600 lift and what would it end up at the valve
Click to expand...

It would depend on rocker arm ratio and the lash but you would have to check it at the valve to see what it is.
 

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the question is how much lost due to the bad geometry of the valve train....not lash...

after thinking about what I had posted...i was in my underwear getting ready for work...but now...the wide awake a 2 am....

the lost will be cos 11 degrees x the amount of lift at the cam......or for example .500 lift at valve which is .333 at cam with 1.5 rockers...

cos 11 (0.981627183) x .333 = 0.326881852 x 1.5 rockers = .490 lift at valve...

cos 11 (0.981627183) x .400 (.600 at valve) = 0.392650873 x 1.5 =0.588976309 at valve.

just remember the lifter and pushrod are NOT moving in the same plane...that is why there is a lost of lift at the valve....
 
Thanks for the lesson 70.
I've always just used "about .020" in less than .500 (advertised lift), and "about .028" in bigger than .500. That came about from measuring a few a long time ago. Also, I think the height of the lifter affects it. The taller the lifter, the shorter the pushrod, and sharper the angle. The higher the rocker ratio, the closer to the shaft centerline the pushrod socket is, and the sharper the angle.
It's been decades since trig for me... But I seem to remember something about that...lol
 
yeah..i usually figure .020 lost....i use 1.6 rockerts on the race cars anyway to make up for the lost of lift...even though there is basically more lost of lift with 1.6 rockers...LOL
 
Higher ratio rockers actually improve the valvetrain geometry on smallblock Chryslers, as they move the pushrod tip towards the shaft, and in the same direction as the lifter angle, thus straightening it out very slightly.

The pushrod angle in relationship to the lifter is measured from the lifter seat to the rocker arm seat (cup/ball). Therefore, the taller the lifter and the longer the rocker arm pivot (lower ratio rockers), the more acute the angle.

However, the flipside of using a higher ratio rocker is that it will multiply the valvetrain geometric losses more than a lower ratio rocker at the valve tip (1.6x as opposed to 1.5x etc). Which basically means, you may get slightly better geometry, but you also lose more proportional lift inherent in the design.

Geometric losses for an average street cam and 1.5 rocker will be at least 0.010"-0.015" at the valve.

Don't forget that W2 style offset rockers increase the pushrod angle even more by moving the pushrod out to the side.

Adding to all this is the fact there will also be losses from rocker arm and pushrod flex as the engine turns over - as much as 0.025" or more depending on how weak your rockers and pushrods are in relation to your springs, and how high you rev the engine (lifter/pushrod inertia and high ramp rates at higher revs can actually flick the lifter off the cam nose - like a springboard - and increase valve lift).

Basically, everything affects everything!
 
Yea I know that math.. In your first post it said 58 and for the life of me I set here trying to figure that one out./.. I just thought it was new math or something.. I am old lol...
 
boosted said:
Yea I know that math.. In your first post it said 58 and for the life of me I set here trying to figure that one out./.. I just thought it was new math or something.. I am old lol...
Click to expand...

I am old too....yes...typo..should have been 58 degrees....sorry for the confusion...

I am a product of public schools...before calculators were invented...slide rules were used in my days..
 
Me too.. But the sad thing is I sat here trying to figure that one out...lol.... And I work for the school district here...


Thanks for the test today..
 
Holy crap! And I though I was a rare one for knowing how they worked.
We were taught how to use them when we were kids. Val's were not allowed. Use the brain or fail.
 
70aarcuda said:
I am old too....yes...typo..should have been 58 degrees....sorry for the confusion...

I am a product of public schools...before calculators were invented...slide rules were used in my days..
Click to expand...

Lucky you, we had to use an abacus, lol.
 
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