Reply to "Rev kit / Valve float"

Frode,

its good to read you are running the "good" lifters. If the motor is falling off there are a few areas to check:

>carburetor too small
>throttle plates not fully opening
>insufficient fuel supply
>air/fuel ratio too rich or too lean
>restrictive exhaust
>ignition performance dropping off
>the ignition timing is off
>camshaft timing is off
>camshaft grind is too mild
>valve float (not enough valve spring, lifter pump up, too much lifter pre-load)

Peak torque at 5000 rpm indicates to me you have a fairly hot camshaft, so the camshaft grind shouldn't be the problem. It would be unusual for peak torque & peak BHP to occur at the same rpm, normally the peak BHP is 1000 to 3000 RPM higher than peak torque. So it sounds as if performance is still dropping off at 5000 rpm. Your dyno operator should know if the fuel supply pressure was holding, and if the air fuel ratio was where it should be. If you are running a 4 barrel carburetor, it should be at least a 750 Holley/650 Demon, preferably 850 Holley/750 Demon to hit your target rpm.

Ocasionally a situation occurs where the carburetor butterflies (throttle plates) do not open completely. One way in which this happens they can hit the intake manifold. With a vacuum secondary carb the secondaries can stick closed, or if the diaphragm is bad, just fail to operate. Dave's point about the exhaust is also well made.

Again, good luck my friend.

George