The RPM of the supercharger is what determines the boost created in the MINI Cooper S. Reducing the size of the supercharger pulley, increases the blower RPM which increases the boost. The reduction size on the pulley increases the blower RPM by the same amount.

AVAILABLE SIZES

Size	Horsepower	Torque
15%	+ 12 hp	14 ft lbs
17%	+ 15 hp	18 ft lbs
19%	+ 20 hp	22 ft lbs

These increases boost from the factory 10.5 PSI to 16 PSI with the different reduction pulleys. The impressive torque increase is what translates into some incredible acceleration. One of the main advantages of going with a reduction pulley over the stock pulley is that you are lowering the RPM where boost occurs which shifts your power band lower in the RPM range.

Please Note:
Taper Bore Pulleys MUST be used with Special Drive Belt 157848.