David Vizard's Idea of Almost Bottoming Hyd. ?

[GARY C]

If a 'hydraulic' lifter had very rapid leak down and say 0.030" total travel, wouldn't it be idea for those borderline 'street' engines running 0.800"+ lift solid roller cams and huge spring pressures, by ensuring constant roller contact for better durability and being immune to pump up/leakdown?

Bill,
That's worth a spintron test if ever -
DV

Isn't this the purpose of a minimum travel hyd roller lifter?

I have an idea for a hyd push rod for this same purpose but doubt it would make it to market, although it would be fairly simple by the time everyone got their piece of the pie it would cost too much to be justified.

[NewbVetteGuy]

The problem isn't with the lifter pumping up, it's with the lifter bleeding down at higher RPM's.
It's like the lash opening up on a solid lifter cam. Not only does it shrink up the effective duration(hurting the top-end HP), it makes the effective valve seating velocity extremely high(causing seat bounce).

Mike,

I've heard you say this a few times and I think I remember you even posting the bleed-down rate of a few different lifters at one point to illustrate the problem.

If the lifter bleed down problem is the larger problem with getting a hydraulic lifter to handle RPM better, then bottoming out a "regular" hydraulic lifter or adding shims doesn't really address the problem, right?

I don't have a great confidence that I fully understand HOW lifters bleed down, but I think it's just oil leaking out where it isn't supposed to due to the internal tolerances not being super tight / precise. --IF that IS the case, doesn't this mean that the real solution to getting a hydraulic lifter to RPM better is to buy a more expensive lifter made with more precise and tight tolerances and the slower bleed down rate that comes with that? AKA "Buy a high RPM-specific hyd lifter" rather than bottoming out or shimming a standard hyd lifter?

Last question: Could running a thicker weight oil help change the bleed down rate given that a thicker viscosity oil should leak through tiny passages slower under the pressures of high RPM?



Adam

[1972ho]

Just something I don’t get with the supposed street driving crowd if you want a high rpm motor why even buy a hydraulic cam and lifters and have to worry about this subject just get the solid cam and zing it how you want.The only racer I know of that even needed a hydraulic camshaft set up were stock eliminator racer and NHRA changed that so anyone can run a solid lifter camshaft and some of roundy round racer and they should change there spec to seeing most of them are running short travel lifters that act like a solid anyway.