This vibration begins around 4000 rpm and get worse the higher rpm. The new 383 crank was balanced and I was wondering what balancing must be done beyond that. I put on a new harmonic balancer thinking maybe that would solve something but still the problem is no better. The vibration seems to be one consistent with an engine out of balance according to everyone who has looked at it. It was a rebuild 1997 LT1 350 that was stroked to a 383. Does anyone have any suggestions?

 

Was the motor internally or externally balanced? If it was internally then you will have to get your flywheel nuetrally balanced...dont ask me how I know

Cody

 

Id also say double check the flywheel/flexplate balance against the motor balance