You are pretty limited to what you can do to a limited...sorry about the pun. The sprint booster just opens the throttle body instantly with no hesitation. No HP gain. Some have went to a larger throttle body, done the tune, exhaust and gained some HP. Only a few have had any luck with adding a s/c or turbo. The ECU has been an issue to get them to perform properly. The SRT is an option to trade up to if you like your XF....different motor, but only in an automatic. This turns some off, but, mine is a handful, so I don't miss the clutch or the gear changing. I drive for a living, so I get to shift enough...