Max Spring Pressure

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2013cossj
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Max Spring Pressure

Post by 2013cossj »

What would you consider to be the maximum open pressure on a flat cam with out a hardened overlay?
mag2555
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Re: Max Spring Pressure

Post by mag2555 »

For extended street usage, or race?
For street usage without a lifter with a EDM hole on its ass end I would say 325 open with a ,842” lifter.

And this assumes that the lifters body is truly made here, of which I believe there is only one company doing such.
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mt-engines
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Re: Max Spring Pressure

Post by mt-engines »

430ish depending on rocker ratio.
David Redszus
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Re: Max Spring Pressure

Post by David Redszus »

Valve springs exert a resisting FORCE not pressure when compressed.

When that force is applied to a specific area, we then have spring PRESSURE.

We can easily calculate (or measure) the spring force. Now we must determine the
area to which that force is applied. Force/area = pressure.

Whether it be a flat tappet or roller follower, the contact area to the cam is a flat line,
of a certain width and length. Length can be easily determined, width, not so much.

Assume a nose force of 400 lbs, and a contact area of(0.60" x 0.010" = 0.006 in^2.
The contact pressure would be 400lbs/.006in^2 = 66,666 lbs/in^2 at the nose.

But maximum valve force does not occur across the nose, it does occur at maximum
valve acceleration which is shortly alfter the valve lifts off the seat and the spring force
is nowhere near maximum. This is the crank angle and cam lobe location where maximum
valve/cam wear will occur.

If the valve train mass x acceleration is greater than spring resisting force across the nose,
we will encounter valve float and probable bouncing all the way to valve closure.

Cam love dynamic behavior is difficult to visualize using words; a well drawn graph would
be much easier to understand.
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Re: Max Spring Pressure

Post by n2omike »

You can do all sorts of math, but max spring pressure depends on expected service life, quality of the components, intensity/acceleration of the camshaft, valve train mass, rocker ratio, oil, oil splash, etc... and even luck. lol

Best thing to do, is to work with someone who SUCCESSFULLY grinds a lot of flat tappet camshafts, and take their advice. Mike Jones (Jones Cams) has done a lot of SFT work. He has the really good EDM lifters and uses the best cam cores available. He would be a good one to call. He did a SFT cam for a buddy of mine that was ran for a couple years in a Gasser with zero issue.

Good Luck
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Re: Max Spring Pressure

Post by rebelrouser »

I wonder how many racing classes still require a flat tappet camshaft? Yes I know you can successfully buy and set up a flat tappet camshaft, but for the majority of my customers I just recommend a roller camshaft hydraulic or solid. Most V-8's since the mid 90's were roller from the factory, kind of the norm now.
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