Chris Vaught wrote:
> At 11:52 AM 5/25/2000 -0700, you wrote:
> >how so you identify valve float. i have a mallory unilite dist, pro master
> >coil, performer rpm intake & cam, holley 600 DP carb. the cam and intake are
> >good until 6500 rpm but at 5500 rpm i get a serious lag in power. i do not
> >think 6500 rpm would be good for my engine but i dont even know if i can get
> >there. i also noticed a big lad when i hit 3rd gear. any ideas.
> >thanks
> >chris in hawaii
> >
> Chris
Chris,
Valve float is a name given to a response of a valve train, consisting of cam
followers (tappets) push rods, rocker arms, valves and valve springs forming a
spring-mass system. As the cam drives this system into higher and higher cycle
rates (frequencies), with rpm, they reach a critical rate (frequency) that
corresponds to the “natural frequency” of the spring-mass system. This causes
the entire train to resonate, much like a violin string will vibrate if a sound
wave of it's frequency hits it, or a singer can break a fine glass.
At this point, the valves cease to seal, and the horsepower ceases to increase.
No further rpm gain be gained, regardless of throttle position. The valves
really are “floating” away from their seat.
The sound is unique, and audible, as a mechanical ‘crashing’, as best I can
describe it. Anyway, it doesn't sound normal, or good. This frequency is
excited somewhere near 5,000 rpm on a stock spring/mass system on the Ford. I’ll
never forget it at 6,200 rpm on my MG, just before it swallowed a valve on a
hill climb!
Steve
--
Steve Laifman < Find out what is most >
B9472289 < important in your life >
< and don't let it get away!>
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