These pulleys are designed to fit Rotrex centrifugal superchargers and are available in a range of different diameters which can be used to alter the speed of the charger for more or less boost. Attention must be made to the specifications of your supercharger model to ensure the maximum RPM is not exceeded. Direct fit for Rotrex centrifugal superchargersWide range of diameters availableAllows the speed of the charger to be altered for different boost and power outputSteel 8 rib designTo calculate the correct pulley diameter apply the relative information from the supercharger specifications to this formula ensuring the maximum supercharger RPM is not exceeded: Max engine RPM x Crank pulley Diameter x Supercharger ratio  ÷ Pulley diameterPlease note: if your supercharger is fitted with the older style single bolt pulley you will need the pulley adaptor to enable these 6 bolt pulleys to fit.