Perrin's lightened crank pulley for the 2002 and up Subaru WRX / STi is engineered to reduce rotating mass, increasing horsepower and torque. Made from 6061T6 aluminum and weighing 1.2lbs, Perrin crank pulley is more than 4lbs lighter then the stock crank pulley. Perrin's pulley is not underdriven and will not affect the life of your engine. The pulley is simply a redesigned, lighter version of the stock crank pulley.
Aftermarket underdrive pulleys are prone to charging and drivability problems, the Perrin pulley avoids these potential problems by exactly copying the OEM piece. The reduction at the crank shaft is effectively the same as removing 100 pounds of weight from your vehicle. Perrin's crank pulley will not wear out engine bearings or the oil pump, and will not add any additional vibration or noise. Installation is straight forward and can be done without jacking the vehicle or removing anything other than the belt cover, belts and stock crank pulley.