it all depends on how light the flywheel is. The ACT is extremely light, something like 6-9 pounds. Thats way too light for an AWD car. On the other hand i have driven wrxs with the exedy fly wheel which is 14 pounds and the car drove fine. Light weight is good but therer is such a thing as too light. as far as the drive shaft goes the only people i know who make a lighter driveshaft is the Drive Shaft Shop. I dont know if its STI or WRX specific but check it out.