Valve Float, can someone explain
Re: Valve Float, can someone explain Valve float occurs when the lifter is "thrown" off the nose of the cam lobe and does not touch the back (closing) side of the lobe. Obviously, this has an adverse effect on power, as the timing of the closing of the valve is now significantly different from what it once was. Additionally, it is VERY harsh on valvetrain parts because, as you can imagine, the "landing" of the lifter on the lobe is not a gentle one. It's a hell of a good way to pop the face off a valve.
The cause, as HumpinSS mentioned, is valve springs that are too weak for the lobe shape and RPM level.
The cause, as HumpinSS mentioned, is valve springs that are too weak for the lobe shape and RPM level.
Re: Valve Float, can someone explain thanks guys
im just going crazy trying to figure out how i lost 6+mph in the 1/4
i have my limiter set at 6800 and ive hit it alot so i am guessing maybe this is where my loss of power is coming from. should find out soon for sure when my heads/cam package gets here in a few weeks.
im just going crazy trying to figure out how i lost 6+mph in the 1/4
i have my limiter set at 6800 and ive hit it alot so i am guessing maybe this is where my loss of power is coming from. should find out soon for sure when my heads/cam package gets here in a few weeks.
6600 rpm clutch dump of death Administrator
Joined: Dec 2001
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From: Texas
Re: Valve Float, can someone explain Valve float
A high-rpm engine condition in which the valve lifters lose contact with the cam lobes because the valve springs are not strong enough to overcome the momentum of the various valvetrain components. The onset of valve float prevents higher-rpm operation. The valves will stay open and/or "bounce" on their seats. The clearance in the valve train created by valve float will also cause hydraulic lifters to "pumpup" as they try to eliminate the valve clearance. Extended periods of valve float will damage the valvetrain.
A high-rpm engine condition in which the valve lifters lose contact with the cam lobes because the valve springs are not strong enough to overcome the momentum of the various valvetrain components. The onset of valve float prevents higher-rpm operation. The valves will stay open and/or "bounce" on their seats. The clearance in the valve train created by valve float will also cause hydraulic lifters to "pumpup" as they try to eliminate the valve clearance. Extended periods of valve float will damage the valvetrain.
Re: Valve Float, can someone explain
Valve float
A high-rpm engine condition in which the valve lifters lose contact with the cam lobes because the valve springs are not strong enough to overcome the momentum of the various valvetrain components. The onset of valve float prevents higher-rpm operation. The valves will stay open and/or "bounce" on their seats. The clearance in the valve train created by valve float will also cause hydraulic lifters to "pumpup" as they try to eliminate the valve clearance. Extended periods of valve float will damage the valvetrain.
A high-rpm engine condition in which the valve lifters lose contact with the cam lobes because the valve springs are not strong enough to overcome the momentum of the various valvetrain components. The onset of valve float prevents higher-rpm operation. The valves will stay open and/or "bounce" on their seats. The clearance in the valve train created by valve float will also cause hydraulic lifters to "pumpup" as they try to eliminate the valve clearance. Extended periods of valve float will damage the valvetrain.
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Re: Valve Float, can someone explain That's called "valve loft", and yeah, I've heard of it too. A controlled float. You measure lift while the motor is off, but you get more effective lift by lofting the valvetrain with a really aggressive ramp on the cam.
-Andrew
-Andrew
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Verdad Gallardo 6600 rpm clutch dump of death Administrator
Joined: Dec 2001
Posts: 4,983
Likes: 13
From: Texas
Re: Valve Float, can someone explain We currently use those cams in a class car that we run. NASCAR uses them too. Comp calls them a "launcher" cam. You find them in classes where you are lift limited. They alos use them in karting. Its controlled valve float. Its really crazy. All of the sudden @ 6200 the acceleration curve on the data computer starts this wicked climb since it gains a bunch more lift... They are VERY hard on cams and on all the other associated parts.
TECH Fanatic
Joined: Jun 2002
Posts: 1,979
Likes: 3
From: Upstate NY
Re: Valve Float, can someone explain Launching or lofting the valve requires very well matched valvetrain components, especially the springs. If it's done just right the "landing" on the closing flank won't be a disaster. If it'll live for a million revs in a Cup race, it can be done correctly.
It ain't cheap to do it right.
It ain't cheap to do it right.
6600 rpm clutch dump of death Administrator
Joined: Dec 2001
Posts: 4,983
Likes: 13
From: Texas
Re: Valve Float, can someone explain True dat...
Lets put it this way, We use Schubeck cool face lifters, 1.2 ratio break in rockers, and pull the inner spring out for break in. My buddy was in a hurry last week, and tried to cut corners and break the cam in with 1.7s. The cam went flat in 7 minutes. New motor is now junk...
Lets put it this way, We use Schubeck cool face lifters, 1.2 ratio break in rockers, and pull the inner spring out for break in. My buddy was in a hurry last week, and tried to cut corners and break the cam in with 1.7s. The cam went flat in 7 minutes. New motor is now junk...
TECH Fanatic
Joined: Jun 2002
Posts: 1,979
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From: Upstate NY
Re: Valve Float, can someone explain J-Rod:
"Haste makes..." You know the rest.
"cool face lifters" ? What are they?
Do you use welded steel cam lobes? It sounds like you might be in that enviornment.
"Haste makes..." You know the rest.
"cool face lifters" ? What are they?
Do you use welded steel cam lobes? It sounds like you might be in that enviornment.
