When you install a lite weight pulley/s you will see a significant performance advantage. This advantage comes from the reduction in rotational mass. Rotational mass is the weight the engine has to overcome to accelerate. By reducing this mass the engine can spool up faster which means better acceleration. A second advantage is available for many applications which is underdriving the accessories. Underdriving is turning the accessories at a lower speed, by making the crank pulley smaller or the accessory pulley larger, so they dont waste any engine power. We custom tailor the underdrive (reduction in speed) to maximize the power advantage without hurting accessory efficiency. These advantages also mean better gas mileage for you. Making UR pulleys a WIN, WIN!