Grimmspeed Lightweight Crank Pulley BLACK - Subaru FA/FB Engines [Equipped w/1-Piece OEM Pulley] - 095023Your factory crank pulley is responsible for transferring energy from your crankshaft to your water pump, a c compressor and alternator. It does this by way of a rubber belt and it does it's job well. The drawback to the factory pulley is that it's quite heavy. Reasons for this include less expensive manufacturing and using the pulley's mass to smooth out 'noise' in the accessory system (NOT to be confused with functioning as a harmonic dampener,