David Vizard's Idea of Almost Bottoming Hyd. ? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 06-20-2010, 08:44 PM
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David Vizard's Idea of Almost Bottoming Hyd. ?

Any comments on David Vizard's idea of almost bottoming hydraulic lifters?

He recommends adjusting rockers with .010" between valve stem & rocker tip with valve barely closed, so the lifter is almost solid.

Claims 200-300 more max. RPM & up to 20 HP, due to small air bubbles in oil in lifter, less lifter compression & less seat bounce.

BBP

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Old 06-21-2010, 04:46 AM
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Intresting...., seems like it would be noisey.
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Old 06-21-2010, 05:35 AM
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20 hp from a lifer adjustment ............. / I will wait and see .

20 hp from a single part is up there to begin with.

Not buying it and not saying it wont.. however my money is on hard to believe for now.
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Old 06-21-2010, 05:47 AM
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I can see how it may give it a few hundred more RPM, but more power I doubt. You can get the same results by doing the old hot rodders trick of "zero lashing" hydraulic lifters which is how I adjust them.
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Old 06-21-2010, 06:51 AM
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The engineer from T&D says hydraulics should be lashed at between 0 and .004". So, who do you believe?
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Old 06-21-2010, 07:23 AM
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Just run solid lifters. The oval track racers make a insert for the hyd lifters that makes them solid. Lash at 0-.003". Most tech people just look at the outside of the lifter to decide if its hyd or solid.
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Old 06-21-2010, 10:11 AM
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Are you talking about zero lashing hydraulic lifters?

Collapsing the lifter and then providing clearance will just float the valve when they pump up.

I used to run "zero lashed lifters" in all my stock head HiPo motors and you get about 200-300 more rpm before valve float sets in. Its a very common thing to do with stock valve springs but you need to be able to lock the adjuster either by double nut (not recommended) or the usual set screw jam nut style as pictured here.

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Old 06-22-2010, 09:47 AM
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He sets the plungers almost solid at the bottom of the lifter.

If you don't float the valves, the lifters shouldn't pump up?

I will check for pushrod oiling.

BBP
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Old 06-22-2010, 10:42 AM
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Joe Sherman recommends this also. I have never been brave enough, or had an engine with enough P-V clearance to try it.
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Old 06-22-2010, 10:57 AM
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I think loss of control of the valve train takes pressure off the lifter plunger & allows the lifter to pump up. Not the other way around.

I'm putting on good Lunati (PAC) Beehive valve springs rate = 370#/in.
213# seat & 414# open.

I have Lunati retro hydro roller cam & lifters, Titanium retainers & 10* locks, strong 3/8" chrome-moly pushrods, & Comp Pro Magnum SS roller rockers, & 7/16 ARP studs.

BBP

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Old 06-22-2010, 11:03 AM
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Well even if it worked (all that trouble for 300 rpm?) you would be screwing up the geometry for the rockers and all that entails. Seems like a gigantic waste of time for little gain and to do essentially what zero lashing does anyway?

Why would anyone do this unless you had a collapsed lifter and needed to make it home?
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Old 06-22-2010, 11:12 AM
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4 Jaw Chuck,

Did you notice:

"Claims 200-300 more max. RPM & up to 20 HP, due to small air bubbles in oil in lifter, less lifter compression & less seat bounce."
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Old 06-22-2010, 11:57 AM
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Quote:
Originally Posted by BUFFALOBILLPATRICK
Any comments on David Vizard's idea of almost bottoming hydraulic lifters?

He recommends adjusting rockers with .010" between valve stem & rocker tip with valve barely closed, so the lifter is almost solid.

Claims 200-300 more max. RPM & up to 20 HP, due to small air bubbles in oil in lifter, less lifter compression & less seat bounce.

BBP
What you do is to let the lifter pump all the way up and adjust it like a solid. To do this you must use a Circlip to retain the inner piston as most hydro-lifters use a wire bail which isn't secure enough to allow it to react the inner piston load so it could fail and let the lifter's guts spill out. A Circlip is strong enough to provide positive retention when the lifter is at full pump up. But you have to keep the sharp machined side of the Circlip facing up so it jams itself into the lifter body's retention groove. The radius side of the Circlip faces into the the groove looking toward the inner piston of the lifter. Otherwise the Circlip might slip out if the radiused side is facing up. At this point you can adjust the rocker to valve stem to zero lash or put in a little negative lash of about .005 inch (sink the piston .005) HOT.

When doing this the lifter will be fully pumped up all the time acting like a solid lifter. It will not be able to pump up to a point where it floats the valve as all its upward hydraulic load will be reacted out of the inner piston into the Circlip, then into the outer body. This will pick up some top end RPM without a stiffer valve train as the lifter cannot pump up to remove any lash that develops.

The problem with pump up in a conventional hydraulic lifter is that it sees any additional clearance as lash and moves to close that distance. At high RPMs this additional lash comes from deflections of the parts especially the push rod where they bend small amounts, or the valve is a little slow to close, or the valve spring hits a harmonic holding the valve open a fraction too long. A lifter adjusted by the book at zero lash plus some down turn of the rocker nut by 1/4 to 1/2 turn sees these slight errors in deflection or timing as a lash to be removed. When the lifter is running on the top of its lash adjusting distance, there is no way for it to move its piston any higher to remove any perceived lash developments so pump-up cannot occur.

One has to keep in mind that all hydraulic lifters leak a little so the actual profile the valve moves is seldom exactly that of the cam profile. Also, you need to keep about .005 more than zero lash as this small movement insures the disk valve under the push rod that feeds oil into the push rod for top end oiling can function. These adjustments are made with the engine HOT and running, otherwise the valves could be held off their seats if this is done on a cold engine.

Bogie
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Old 06-22-2010, 01:33 PM
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OP- can you please provide a link to the Vizard instructions you cite?
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Old 06-22-2010, 01:59 PM
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He uses a .006-.010" feeler gauge between the valve stem & the rocker tip, while running motor at 1,000 RPM

He tightens the rocker stud nut until there is a slight miss from the valve not closing all the way, backs up until miss goes away.

This makes the hydro lifter plunger .010-.020" from bottoming out inside the lifter, depending on rocker ratio.

It's in his book: How to Build Max Performance Chevy Small Blocks On a Budget.
Pg 105-106

BBP
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