The crank pulley is bigger. If you were to change the pulley on the S/C, then it would be smaller. Some of the first mods had the smaller S/C pulley, but there was significant slippage with the smaller size. Most mods now increase the size of the crank pulley.
You can purchase the same pulley that ASP sells from JDS Performance and save yourself about $85 ! LEt me know if you need a phone number....and don't forget, you'll need a longer belt to go with it...the girl at ASP can give you the part number then you can order that as well from David at JDS....and you'll love the difference in power!!