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I'm in the process of getting my 331 together. Right now, I'm at the point where I need to index the cam and get the right length pushrods. I've found that I need to shim a good .200" to get the smallest swipe on the valve stem.

I have an adjustable push rod to measure length, but I need to know that I'm measuring correctly. What I've found is there's a good .050" of plunge in the lifter's plunger that I can move with my fingers. But after that, the plunger is solid. So my question is do I size the pushrod to keep the plunger pushed in that .050" or is that plunge movement needed to push oil up the rod? My assumption is the oil pump pressure will get the oil from the lifters, up the rods, and to the top of the heads. But before I made that assumption, I wanted to confirm from those that know for sure. I'm hoping that assumption is good otherwise a portion of the cam's lift is lost to pumping the plunger.

Thoughts?

For those that find this thread and wish there'd been more info, here's where it was discussed over on EECTuning.org:
EECTuning.org>How to size pushrods

Discussion in that thread ranged beyond pushrod measuring and includes different strategies on dealing with preload and the effects of too much and not enough preload.

Don't push in on the lifter when measuring. It will fill with oil and be pressurized.

Yeah, what Malcolm said, it will still move but not nearly as easy as it is now.

It seems that most people do preload the lifters just to make sure there isn't slop and then shim for what they want. There are some that preload most of the plunge out the theory being that yes the lifters to solidy at higher RPMs...in other words the lifter lifts and drops faster than it can relieve the oil out making the lifter effectively solid. However at low RPMs like idle and near idle conditions, there IS enough time to squish the lifter down which affects the cam's effective duration and max lift values at those lower RPMs. Some consider that a good thing on high performance cams that have "too much" duration and need less duration on the low end, so for those applications, they commonly just barely preload the lifters. But in mild cam applications where the engine isn't spending a lot of time at high RPM, it seems a common thing to do is preload .050-.100" out of the plunger action to reduce how much they bleed down on cams that already don't have a lot of duration. In fact, most people use those FMS shims for that very purpose. Buy rods that are .100 shorter than they measure, then shim for the difference OR use adjustable rockers if the budget can afford them.

The only time I found that preload is a bad thing is at high RPMs with high pressure oil pumps. What happens then is when the lifter reaches the height of the lobe and starts rolling down the lobe, the oil pressure starts pushing the lifter down the lobe faster than the valve spring can push the valve train down to track the cam. This causes the preload area to fill up with oil also known as lifter pump-up. When the lifter is back on the base circle of the cam, the valve is still being held open by the oil in the lifter. The bleed down can only happen at a certain rate. But as RPMs increase, the "effective" duration gets larger and lobe center of the cam starts retarding which can be bad. This is the #1 reason high performance applications always use solid lifters...to avoid pump-up and to get a consistent cam behavior through the RPM range. But since all solid lifter require lash, you have to run a wider duration and slightly higher lift cam than you would with a hydraulic setup to account for the slop created by the lash.

Does that sound at all plausible?

Humm my buddy had to use a solid lifter cam in his 496 big block. I forget the exact reasoning he told me but I recall he couldn't run as aggressive cam as he wanted in a hydraulic setup. I imagine what you said because it sounds plausible. I could ask him again. I don't deal much with super aggressive cams, just not my thing. I prefer smooth cams that ride nice and idle well. I make power with boost.