twin disc is over rated for 500whp. 500 is simply not enough to justify spending 1200 on it. I was perfectly fine making 630hp on a stage 5 competition clutch with zero clutch slippage on the track with slicks. This was the non upgraded version, the upgraded version has the retarded pressure plate that will just piss you off driving it cause its so hard to press and it doesnt grip anymore then the non upgraded version. stage 5 for the win. 650+ get a twin disc, its the torque that will spin your clutch...anything over 400 usually makes a stage 5 start to slip, BUT THATS ON THE DYNO.

as for spec clutch, they apperently have a really good twin disc, but thats IT.