Big Al

iTrader: (1)

Was arguing with a friend of mine about what hydraulic lifters do at high RPM. We call it lifter float or "pumping up." He claims it's not that the lifters are "floating," they're collapsing. He's telling me what we've been doing for 50 years is setting the lifter loose so they can't pump up and in reality we should bottom them out and let off a tiny bit so when they collapse they still work and recover quicker.

Any comments on this? If he's right my push rods are too short! And if he's right I want to apologize to everyone I thought I was helping with valve lash setting

Al 95 Z28

nitrous2fast

iTrader: (2)

He is very wrong. the problem is that the lifter has enough pressure that it actually pushes the push rod up enough that the valve doesn't contact the valve seat creating a gap/leak. This is why the motor looses power when the lifters pump-up.

BUT there is more than one reason they "float". Not enough spring pressure is one of the main causes of float. The spring has to act against the valve, rocker, push-rod, and lifter. Now add in a lifter holding all of its oil, creating a no pre-load situation, and bam you have valve float.

Big Al

iTrader: (1)

Found this:

http://www.chevyhiperformance.com/te...ams/index.html

This is from the page:
The biggest problem with hydraulic-roller cams is that the tall lifters are heavy. The added weight makes it difficult to control at high rpm without using stiffer valvesprings. Unfortunately, heavy springs tend to collapse hydraulic lifters at high rpm. AirFlow Research sells a Hydra-Rev kit for the small-block Chevy that adds rpm by adding spring pressure to control the lifter body.

Read more: http://www.chevyhiperformance.com/te...#ixzz1QMExj6hK


Al

gregrob

iTrader: (8)

Ask him if that's the case, why high performance lifters are fast bleed? The fact is they can't get rid of enough oil at high rpms and pump up..

SS RRR

iTrader: (2)

Exactly. If his theory was correct the valve geometry would be so out of whack it would cause catastrophic failure. It would also mean pushrods and lash would have to be measured with the lifter bottomed out.

Wicked94Z

iTrader: (26)

hydraulic lifters don't bleed down, oil is incompressible and the valving (if operational!) in them prevents bleed down. Machining tolerances come into play here, and the spendy billet lifters have an advantage here. When you have a finely machined lifter, with essentially no bleed down, you don't really need much oil flow to keep the lifter preload where you set it, which keeps you from pumping the thing up at high rpms and hanging a valve. If you unload the lifter (float or loft or whatever the ls1tech "elite" want to call it) it will pump up in a hurry, that is the reason these rev kits exist for hydraulic rollers, the power fall off is so pronounced in a hydraulic valvetrain vs a mechanical valvetrain. 350/900 is the highest spring pressures I've heard of on a hydraulic roller lifter, they were spinning over 8500 rpm through the lights. It was worth a solid 1mph over the 300/800 springs they were running, which is incredible on a stock 5.0 camshaft and FRPP cast body lifters.

Wicked94Z

iTrader: (26)

As a general rule, the spring pressures need to be roughly 220/550 to run a lifter successfully off the bottom. Mods need to be done on the lifters to keep them solids.

96lt1m6

iTrader: (31)

Hmm run a hydraulic lifter too far down and it runs like poo and wont idle properly nor will it RPM decently. My car runs at its best when the lifter is adjusted 1/8 turn from when it becomes quiet during adjustment. I also adjust my rockers with the motor running......set it and forget it!

96lt1m6

iTrader: (31)

Wicked hit it on the head right there!!!!!!!!!!! I am impressed that a heavy *** hydraulic lifter can live at that rpm for as long as they do!!!!!!

Wicked94Z

iTrader: (26)

Eh, the drop in lifters aren't really that much weight compared to the solid roller stuff. Those guys have alot of trick stuff ($$$) going on the quick side of the valvetrain. Think about the inertia of a 125g lifter going up the ramp, and then a 270+gram valve/spring/retainer/lock combo accelerating 1.6 times faster and lifter weight doesn't mean as much as people think below ~7500rpm. Higher than that and it's harder to keep the lifter following the closing ramp, which is where 99% of valve float happens on these hydraulic roller setups to begin with.

Pushrods have a lot to do with it... I have spintron data of a 7/16>3/8 tapered pushrod flexing ~.030" on the opening ramp (first 15 degrees) of solid flat tappet cam. Here's the kicker, it was only 150lbs seated and 650lbs open at ~.850 lift. That pushrod is about 300% stiffer than a typical 5/16 .080 wall the usual LT1 combo runs and people wonder why a properly setup solid roller setup runs so well in comparison to an average Joe's HR?

Big Al

iTrader: (1)

http://performancetrends.com/Definitions/Lifters.htm

http://www.speedtalk.com/forum/viewt...2f00d87b508a47

http://www.gofastnews.com/archive/index.php/t-1200.html

Looks like there is a lot of info out there.

Al