You buy the pully AND the special puller to remove the old and install the new one. IMO, it's just not worth the cost, about $300-$400, and the cost of a new blower when you burn the bearings up. Maybe, and just maybe, an aftermarket K&N filter and cat-back system. I say maybe because theres no real proof they help. Just alot of seat-of-the-pants dynos.