Collapsing a lifter
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Registered User
Joined: Apr 2004
Posts: 1,347
From: Austin/Houston, TX
Collapsing a lifter
Ive asked quite a few people and havent gotten a straight answer. What is the max pressure the stock lifters can handle at 6500 rpm?
The springs that i have are comp 941's on a cc306 cam. I have calculated the spring pressure (at the valve) with the 1.5's to be 363/376 lbs and 378/392 lbs with the 1.6's.
Im assuming that the pressure on the lifter can be found by multiplying the spring pressure by the lifter ratio, correct?
If this is so, i calculated the lifter pressures to be:
545/564 lbs (1.5)
605/627 lbs (1.6)
That sounds like too much for the stock lifters at 6500 rpm like the cam wants to go.
Thanks alot,
Stu
The springs that i have are comp 941's on a cc306 cam. I have calculated the spring pressure (at the valve) with the 1.5's to be 363/376 lbs and 378/392 lbs with the 1.6's.
Im assuming that the pressure on the lifter can be found by multiplying the spring pressure by the lifter ratio, correct?
If this is so, i calculated the lifter pressures to be:
545/564 lbs (1.5)
605/627 lbs (1.6)
That sounds like too much for the stock lifters at 6500 rpm like the cam wants to go.
Thanks alot,
Stu
Registered User
Joined: Oct 2002
Posts: 2,931
From: Upstate NY
You've calculated the theoretical static load the lifter might see, but dynamically it sees very different loads. The loads are related to the acceleration the lifter sees as well as the spring loads. F= ma applies.
In some cases, like when the lifter is decelerating as it nears the nose of the cam (where spring loads are greatest), the deceleration can pretty much unload the lifter. Think valve toss or "float". This is rpm dependant.
I can't answer your question. For one thing an analysis would require all the masses of the valvetrain parts to determine the loads at 6500. That still wouldn't tell you whether stock lifters would work, or more specifically, if they would work well. With some simulation programs you can plot pushrod forces which would give you an idea of lifter loads. The highest loads were at the beginning and end of the valve's travel, especially at 6500 on an engine I just looked at.
My guess is that IF the cam lobes are not too aggressive and IF the valve train parts are light enough, and IF the spring pressure is just enough to control the valve motion, stock lifters might work well at 6500.
I'd ask Comp or my cam designer for recommendations on lifters.
My $.02
In some cases, like when the lifter is decelerating as it nears the nose of the cam (where spring loads are greatest), the deceleration can pretty much unload the lifter. Think valve toss or "float". This is rpm dependant.
I can't answer your question. For one thing an analysis would require all the masses of the valvetrain parts to determine the loads at 6500. That still wouldn't tell you whether stock lifters would work, or more specifically, if they would work well. With some simulation programs you can plot pushrod forces which would give you an idea of lifter loads. The highest loads were at the beginning and end of the valve's travel, especially at 6500 on an engine I just looked at.
My guess is that IF the cam lobes are not too aggressive and IF the valve train parts are light enough, and IF the spring pressure is just enough to control the valve motion, stock lifters might work well at 6500.
I'd ask Comp or my cam designer for recommendations on lifters.
My $.02
Registered User
Joined: Nov 2002
Posts: 588
From: Indiana
Comp can tell you what they like for that cam. My cam designer told me that the stock lifters were good to about 400 lbs. open. He was OK with spring pressures to that point, but got more nervous the closer I got to 400. I've heard others say lower numbers. I used his numbers since it was his cam. I'm at 380 intake and 388 exhaust and they work OK. That said, I doubt they will last as long pushing them that hard. Mine also runs to 6500, FWIW.
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