The ALTA 15 % supercharger pulley will increase your MINI's horse power by 15WHP. This happens by reducing the size of the supercharger pulley which in-turn spins the super charger faster to create more boost pressure. No additional modifications to the engine or ECU are required.The ALTA supercharger pulley features a stainless steel supercharger shaft coupler with installation site aperture and direct torque technology. The ultra light aluminum body decreases rotational inertia and overall weight. Over-sized belt retainers and grooved teeth increase belt grip.Choose between a 15% or 17% pulley the higher percentage will add more boost horsepower and torque.