APR's Supercharger Drive and Crank Pulley Upgrades dramatically increase horsepower and torque by increasing the rotational speed of the factory supercharger. APR's Stage II Pulley ECU Upgrade makes the necessary engine management adjustments to handle the increased supercharger speeds, and in turn allows the engine to create more power. The pulleys are sold separately, allowing for multiple levels of performance, each of which builds upon the other. Finally, when combined with APR's Ultracharger Throttle Body Upgrade in a dual pulley setup, the system is alleviated of power robbing inlet restrictions, allowing the engine to achieve exciting new levels of performance! APR's Supercharger Drive Pulley Upgrade decreases the diameter of the factory pulley from ~63.25mm to 57.75mm, which in turn spins the supercharger ~9.5% faster. This results in a healthy bump in horsepower and torque across the entire RPM range with the supercharger operating at a higher rate of speed. The pulley is CNC machined from billet stainless steel, e-coated black for an OEM appearance and is press fitted to the factory supercharger.