Shown left and right of a stock dia. Race Crank pulley in the picture to the right, this Underdrive pulley was designed for guys that would like to run electric water pumps on their Turbo Buicks. The size of this pulley is crucial for the proper operation of the serpentine belt system when running an electric water pump. If the pulley was any bigger or smaller there would be belt rubbing problems. This pulley takes all of the guess work out for you and makes electric water pump installation easy.