No, you are correct. It is an old skool V-8 trick. Well, so much for that great question.

 

I always thought that valve float was when the valve would stay open for too long and sometimes hit the piston. I also thought that it was when the intake and exhaust valve would be open at the same time. Valve float would happen when your valve springs werent strong enough to keep the valve shut at high rpm or high horsepower application. Well thats what I thought so what is it really???

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by earl &raquo;</TD></TR><TR><TD CLASS="quote">No, you are correct. It is an old skool V-8 trick. Well, so much for that great question.</TD></TR></TABLE>

alot of go-kart racers do this as well...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mista Bone &raquo;</TD></TR><TR><TD CLASS="quote">Valve float = when the valvesprings cannot close the valves quick enough to meet the cam profile.</TD></TR></TABLE>

So then why would anyone need stiffer valvesprings just because your turbo and makeing more power?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mista Bone &raquo;</TD></TR><TR><TD CLASS="quote">Valve float = when the valvesprings cannot close the valves quick enough to meet the cam profile.

Valve BOUNCE is a whole different story!</TD></TR></TABLE>



valve float is not piston to valve contact...even though it sounds nasty....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by pornstarSR &raquo;</TD></TR><TR><TD CLASS="quote">



valve float is not piston to valve contact...even though it sounds nasty....</TD></TR></TABLE>

But wouldnt valve float cause piston to valve contact??

 

it can...doesn't always. but it can still be damaging to the cams even if the valve doesn't contact the piston.

 

You get valve float if your ramp rate on the cam is to steep for the spring pressure being used, in conjunction with the weight of the valve train/actuation being too heavy. Or excessive rpm causes a combination of these thresholds (weight and ramp rates) to exceed the spring seat pressure.

 

Shall we begin discussing higher order derivatives? Jerk? Ping? Puff? Finiteness through the fifth time derivative [and continuity through the fourth] will ensure a good cam design, and help prevent valve float within the cam/follower's operating RPM range.

 

forced induction??

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by r7 &raquo;</TD></TR><TR><TD CLASS="quote">forced induction??</TD></TR></TABLE>

 

Valve

Any of various devices that regulate the flow of gases, liquids, or loose materials through piping or through apertures by opening, closing, or obstructing ports or passageways.

Float

To cause to remain suspended without sinking or falling.


Valve float, When a valve is suspended above its seat neither seating nor opening inhibiting the engines ability to create compression, thus power delivery will cease untill the RPMS or boost is decreased untill the valve is able to settle down on its seat properly, depending on the situation in which valve float was caused.

no?

 

true "valve float" never really happens.

It is valve bounce, where the valve springs cannot keep the valve head on the seat after closing. The valve "bounces" off the seat, then closes.

Also called valve flutter if your old enough.

 

That is why, when valves are floating, you hear a loud popping misfire from the motor. It fires back into the intake or exhaust as the valve is bouncing open. On the intake side, you also have turbo boost pushing on the back side of the valve (trying to push it back open).

 

Valve float truly does exist.I've seen lots of high speed film of valve train motion.A "Spintron" is what cam companys and Nextelcup teams use for developing cam profiles and valve train parts.Its a machine that spins an engine on a test stand and takes closeup high-speed video.I've seen valve springs in motion that are not touching the retainer or head.They simply can't expand fast enough.When this happens sometimes the piston catches up with the valve.This is always bad. Seat bounce is what gives you that high speed skip.You can see it on the engine dyno sheet,and everyone with a clue can hear it in the shop when it happens on the dyno.This will eventually break parts but happens when there is plenty of distance from the valve to the piston.
Glenn

 

So valve bounce can be caused by lots of boost pressure? I thought it was mainly caused by over revving the engine. How much boost can stock valvesprings handle?

 

your "bounce" idea is when then valve "bounces" of the piston??????

My "bounce" is when the valve SLAMS shut but not enough spring pressure to manintain closure.

Basically, we are both mentioning the same thing in different time.

NEITHER is good!!!!!!!!