Valve Float
Thread Starter
TECH Regular
Joined: Mar 2006
Posts: 471
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From: Rolesville, NC
Valve Float Valve Float, How does one regonize it ( dyno chart Hick up?)
What causes Valve Float?
and how do you correct it?
I think I understand some of the problems, but additional input would be great.
( my search function does not work with Firefox & Ad Blockers)
TIA
Tom
What causes Valve Float?
and how do you correct it?
I think I understand some of the problems, but additional input would be great.
( my search function does not work with Firefox & Ad Blockers)
TIA
Tom
Valve springs that arent good enough and lifters. When we tore my motor apart it was bad, engine builder said it was the stock lifters that caused it, sprnigs were fine. You will notice power loss in upper RPM's if its bad enough. Dunno bout a dyno though, guessing lower readings.
TECH Apprentice
Joined: Aug 2004
Posts: 321
Likes: 0
From: Buffalo, N.Y.
VERY BASICALLY, valve float is caused by the valve spring's inability to control valve timing events. Usually, weak valve springs (or using valve springs that are not suited to a particular cam's "profile" ), over-revving, heavy valvetrain, etc.
At too high an RPM (or simply throwing in a lumpy cam with springs too weak to control an aggressive profile), the valve spring just can't react quickly enough to open/close valves at the proper time. Valve float can cause nasty things to happen, like leaving a valve "hanging" just that fraction of a second too long, and allowing it to make contact with the piston before it can close.
There's no mistaking valve float; your engine will feel like it's falling on its face, and power loss will be easily noticeable. Things like using any of the dozens of "hand-held" tuners on the market to screw with rev limiter settings, or installing mis-matched cam/valve spring combinations are things to avoid.
At too high an RPM (or simply throwing in a lumpy cam with springs too weak to control an aggressive profile), the valve spring just can't react quickly enough to open/close valves at the proper time. Valve float can cause nasty things to happen, like leaving a valve "hanging" just that fraction of a second too long, and allowing it to make contact with the piston before it can close.
There's no mistaking valve float; your engine will feel like it's falling on its face, and power loss will be easily noticeable. Things like using any of the dozens of "hand-held" tuners on the market to screw with rev limiter settings, or installing mis-matched cam/valve spring combinations are things to avoid.
Dyno chart will show it, its one of the things I always watch for. Harmonics will also show on the dyno, where you hit a natural frequency but the valve train recovers at a higher RPM. True "float" won't recover.
My valve float on the highway felt like it just stopped revving, or on cruise control at 6800RPM... it would reach about 6800RPM, then after 6 seconds it hadn't yet reached 6900, and my rev limiter was 7200. The scanner log from the same run shows the MAP readings bouncing around from low 90's to mid-100's. Never ran the dyno above 6800, but the curves were a little more jerky above 6700.
