I got my new 383 up and running and what not, but now I notice a horrible vibration and it gets worse with higher RPM's. When my engine was orginally balance the machine shop balanced it with a new flexplate that they remove the weights off of because they said the motor was now internally balanced. Turns out that the new flexplate is the wrong one, it was too big. So we were forced to use the stock flexplate that is weighted during the motor swap. Could It be the stock flexplate causing this horrible vibration?

 

Sounds like you need to remove that weight from the flexplate you are using.

 

Yes you either need to remove the weight or get the proper flexplate.