A 15% reduction in the supercharger pulley diameter of the MINI Cooper S increases the boost of your MINI Cooper S by more than 4 pounds, resulting in a dynomeasured gain of over 20 horsepower AT THE WHEELS. Maximum boost is achieved at lower RPM, giving more power in the midrange of your MINI Cooper S. Fits 20022006 R53 MINI Cooper S and 20052008 R52 MINI Cooper S Convertibles. Does NOT fit 2007+ R56 MINI Cooper and S, and does NOT fit the R55 MINI CLUBMANS. [ ] Unique 3piece supercharger pulley selfaligning design delivers superior clamping force, and doesn't pull back from the stop when tightened like 2piece designs. [ ] The new built in stop locates the supercharger pulley in the proper position, simplifying installation. [ ] Optimum 15% reduction avoids overspinning supercharger and excessive intake charge heat generated by smaller supercahrger pulley upgrades. [ ] Includes correct length belt for proper tensioner operation. [ ] Lightweight design with low rotational mass spins up faster than heavier steel supercharger pulleys. The removal of the stock supercharger pulley requires a special pulley removal tool. If you are considering our pulley upgrade, take a look at NMK5041 for a kit that includes a rental pulley removal tool. How Small is Too Small? Supercahrger pulleys reduced 16%, 17% or 19%, or using an oversized crank pulley, may spin the supercharger faster than our 15% pulley, but most of the additional boost cannot be used and can contrubute to engine and exhaust system damage. These smaller pulleys cause the supercharger to operate at higher RPM than it is designed to tolerate at redline. Plus, the Roots type supercharger drastically looses efficiency at higher RPMs, generating excess heat as it tries to compress more air. In the process, it further overloads the barely adequate airtoair intercoolers and causes the ECU to enrichen the mixture and pull back on ignition timing to preserve the engine. This results in lost power, poor fuel econom