[olddog]

The tranny should not matter, but the flywheel does. The flywheel is out of ballance (not nuetral) to compensate for the crank shaft not being completely ballanced. Same is true for the ballancer on the front.

For high performance engines they try to get the ballance to +/- 1 gram (there are 454 grams in a pound). If you have 50 oz flywheel and ballancer on an engine that should have 28 oz, the engine is out of ballance by 22 oz or a 1-3/8 pounds. That would be huge!

I have no experiance with this, but I would expect the motor vibration to be worse than you described. A nieghbor put a SB chevy 350 damper on 400, when the 400 first came out. He didn't notice the vibration, but the damper went through the radiator, when it came off. It took the keyway out of the crankshaft on its way off. Seems to me the bolt head snapped off, but I'm not sure anymore. So if he didn't notice the vibration, maybe what you have at the upper rpm is all the warning you will get.

To sum it up I am concerned for you.

They do make flywheels and dampers for both 28 & 50 oz, so what you need is available. The question is how do we get you some help to sort out what you need for sure.

Not to high jack this thread, so back to the origonal poster. Since 1bad66 may have had the wrong weighted flywheel and he had the same vibration at the same rpm as kens67cobra original post. I have to ask, are you sure you have the right flywheel on your engine? I think this is a common mystake.