APR's Supercharger Crank Pulley Upgrade increases the diameter of the factory pulley from ~162mm to ~187mm, which in turn spins the supercharger ~15.4% faster. This results in a larger bump in horsepower and torque across the entire RPM range, as the supercharger is spinning at an even higher rate of speed. The pulley retains the factory harmonically balanced crank pulley and bolts on top of the existing unit. It is CNC machined from light weight billet aluminum with weight saving pockets throughout. It has an anodized black finish and includes new crank pulley bolts.