Valve float?

Hello.I have measured my spring hight and found that exh.was installed at
1.72 not the 1.75 it supposed to be.118@1.72 instead of 110@1.75.
Now int.was 1.79 that is 99@1.79 instead of 110@1.75.
Should I shim it to 1.72 and hope it will be ok.
Cam is comp292H and I feel it don´t want to rev over 6000rpm.
Could this be the problem?
How do I notice valvefloat?
Motor is a 289" with ported heads and 1.94-1.60 valves.
I have uppgraded the fuel line to 3/8" from the pickup and all the way.
Thank´s
Gresse

Actually, the best way to do it is to use a spring tester to measure the height to get the seat pressure you need, then measure the head to retainer distance and shim as needed. You can add shims if you want to, but 10 lbs is not likely to make a lot of difference. Lifters giving it up make the car kind of go "flat line" and quit pulling. Valve float may induce popping, etc because stuff is hanging in the breeze. It's also a good way to toss the rods.
[addsig]

Thank you.The car don´t pop at all it just quit pulling.
The lifters are comp cams magnum I think they called them.
It came with my cam.How can lifters give up?
Gresse

When the valves "float" the lifters (hydraulic) "pump up" (fill up with oil) and hold the valves open until they bleed off. You lose cylinder pressure until the lifters bleed off.

Actually it's just the opposite, the oil galley pressure can't replace the oil thats shoved out from the force fast enough - and your effective lifter height ends up less, letting the valve just hang in the breeze, where the oil should be shoving the plunger up to take up the slack as the lobe descends. When the valve goes to open again, the lifter is still relatively empty of oil, and you have to move the lifter a lot to even start opening the valve - losing power.

Valve float can either be seen a loss in power, or heard as an audible buzzing/clacking sound when you reach a certain RPM. In the latter case the lifters are actually coming off of the cam and slamming back onto it, as your springs aren't powerful enough to push the lifter back down. This can occur even on solid lifter engines. If your springs are powerful enough to keep the lifter on the cam, you get the second case, and just lose power because your effective valve lift goes way down as the hydraulic lifters can't keep themselves pumped up.


<font size=-1>[ This Message was edited by: thekingofazle on 3/15/07 4:45am ]</font>

Okey I think I got it.Can I reduce the problem with a high pressure
oilpump?Or should I have to buy a mech cam(like the comp282s)and
be good?
Thank´s
Gresse

You bandaid the problem with special rapid bleed down lifters and/or by setting the lash right at the top of the lifter travel. HOWEVER - if the lifters are not designed to run at the top of travel by having really good retainers, you run the risk of breaking a lifter retainer. If the lifter comes apart, you got big problems.

Note - the described problem can also happen with inadequate fuel delivery. And timing.

If the lifter comes in with less effective height, the valve won't open as far. It will only hang in the breeze if the spring can't control it. Rapid bleeddown lifters are designed to not trap oil when the lifter goes by the oil port too quick.
[addsig]

The way I understand "valve float" is that the ability of the springs to control the action of the valve has been exceeded. Usually rpm is in excess of what the springs can handle compared to the mass that is motion (the valve, pushrod, rocker arm). When the cam has reached the max lift and starts back down, if the lifter, pushrod and valve combination keep going (the valve keeps opening farther even though the nose of the cam has passed max lift) that allows the lifter to pump-up, then you get the resultant missing until the lifter bleeds back down. The valve, pushrod, rocker arm combination keeps going because there is not enough spring pressure to control the amount of mass/rpm combination. Anyway, that explanation always sounded reasonable to me.

You have really got a problem. When I did you that cam, it would rev up to 7000 RPM no problem.I use 120-125 on the seat, 300 lbs open. The way you have the springs COULD be your problem.
JOE SHERMAN RACING

Thank you.This I found on my springs:Erson E915005 chrome sillicone.
1.220"-0.860" 110@1.750-252@1.225" coil lbs/inch:1.125
Rate270 max .525
I could shim to 118@1.720 but my open pressure maybe to little.
Maybe my longtube 1.1/2" headers is holding it back to,but my 3"
exhaust will be okey,right?
Thank´s for your replys.
Gresse