nothing, basically a well running stock motor. I keep up with the maintenance and make sure it's tuned well. nope, all stock. You forget that they now offer 3 different types of exhaust for the Mustang (LM1, LM2, and ProFlow). Each one is progressively more quiet. As far as being primarily a GM company, how about a little history lesson for you? SLP was founded by Ed Hamburger who was the 340 Mopar super stock racer. So I guess you can say it was Mopar first, then GM, then Ford, and now they're getting back into Mopar again.