This Procharger supercharger system is designed to increase horsepower on your Mustang GT by 55% at 8 psi of boost. If you want bolt on horsepower and have no plans to modify your existing engine, The HO kit is for you. For the enthusiasts that want more and are willing to alter the current configuration of their shortblock, the ProCharger Stage II Systems and the Tuner Kits will yield higher horsepower gains. 11 and 10 second quarter mile ET's are right around the corner.