the a6 bottom end is the best too turbo due too the stock girdle. i talked too Mike Yonke at yonke racing and he confirmed that is stronger and hes got a 500hp z6 i believe. a block guard is a MUST. im with lilneedle on the balancing too. as long as youre not talkin it too 9k, youll be aiight. bottom end: forged pistons, eagle rods (ls will work, but you have too knotch the block), block guard, micro polish the crank, BALANCING. youll be good too go. d-series.org will help a lot.