Novawagonmaster can probably answer this better than I. He just made mods to the 6 speed exhaust. However my opinion is...you should give it a try. From what I have seen and read, the 6 speeds have a much better muffler. On challengertalk they have a picture of the suitcase muffler cut open....it is horrible. So you are one step ahead of us auto guys with your stock mufflers.