If you have the latest flash on your truck the 6.0 has to have a little backpressure! Thats just what the ford place told me! They said the 7.3 it doesnt matter bout back pressure b/c they dont have a EGR so thats just what i heard.Heck if you dont wanna blow 400 dollars you can just put a straight pipe on your stock system but the mandrel bend makes everyting flow so much better!