Active Autowerke Underpulley Kit (E9x M3)Description: The BMW S65 V8 engine as used in the BMW E9X M3 does not make available all of the horsepower that the engine actually produces. This Power Pulley KIT through a redesign of the crankshaft outer pulley, actually releases this developed and available horsepower. This performance product is designed to not only to make available horsepower but to still retain all the inherent qualities of your BMW E9X M3 without sacrificing reliability.