ive got this aluminum flywheel that i installed and im not happy with the vibration it produces above 3000 rpm anyone know why it does that.

 

I have a Spec alum series 3 clutch with an alum fly. Internal balance 383 assembly, so, I have a neutral balance. The fly came with an insert for a stock external balance assembly. I did not attach it to the fly. I have not had any problems with vib. Also, I think the stock crank dampner is also balanced for the stock external assemblt. I went with a power bond neutral from Jegs. Hope this helps. B.

 

I don't know what all they did in your rebuild, but on a stock LT1 the rear of the crank is balanced using the flywheel or flex plate. Therefore, if it was rebuilt using a stock crank, the aluminum flywheel would have had to be balanced with the assembly.

If it was just swapped out for the stock flywheel as it was, that is your problem.