The Kartboy crank pulley is milled from a shiny block of billet aluminum. Unlike some other manufacturers, Kartboy doesn't make the lightest possible pulley -- although at two pounds, it's still about 60% lighter than stock. The mass of the pulley is enough to not upset the ECU, which is nice, especially if you have (or will have) a lightweight flywheel.
(If you haven't heard of this problem, if you put a lightweight flywheel and crank pulley on a Subaru motor, the ECU can get upset because it sees the crank speed accelerating faster than it thinks it should, which can result in a Check Engine light.)
The Kartboy crank pulley fits all 2002+ WRX and WRX STI. The diameter is the same as stock, so standard belts will fit fine.
Note that 2008+ cars have a stretch-fit a/c belt with no tensioner. Fitting this belt with the aftermarket pulley is difficult, and there is the possibility of tearing the belt in the process. You have been warned.
