We know that opening up the inlet and sharpening the tuning are tried-and-true methods to improve Mustang performance. The '13 Shelby GT500 likes these mods a lot. The power and torque gains come on in chunks and build across the entire powerband. Adding the smaller pulley simply expands on those gains with more substantial gains across the curve. The peak gains from the Power Pack were 102.33 lb-ft at 4,100 rpm and 91.18 horsepower at 5,600, but it's the movement of the entire curves that you feel in the seat of your pants