One of the easiest ways to free up additional horsepower is to swap out the stock accessory pulleys with a 2005-10 Mustang performance underdrive pulley kit. These Mustang underdrive pulley kits are direct bolt on and available in CNC machined aluminum finishes with SFI approved crank pulleys. Upgrading to a set of 2005-10 Mustang underdrive pulleys can also help increase gas mileage as well as performance.