How important is balancing?
 

I'm building an S4T2 block with S5NA internals with new counterwheights and light flywheel, is it nececary to get the rotating assembly balanced when i'm going to run stock rpm's?

Are the rotors matched?

Riz.

Yes.

I'm doing almost the same thing, fd rotors(matched),flywheel and counterweight, but with an RX8 e-shaft, my builder said a balance was unnecessary for the street.

But, I haven't run it yet.

its not needed. i did have the P port balanced, and it IS noticeably smoother even in the sub 7000rpm range. i started with NEW rotors, eshaft, even the rear CW.

so balancing is not needed, provided you're running matching parts (all S5, or all S4), but its nice

Going back to school after the summer, so i can't afford nice :P