Well.......I don't know about the 1hp gain. What other mods was he doing as well. The motor can only put out what it takes in! So if you change the exhaust without changing air flow (increasing it) you will not get much of a change. I personally are putting air pods with PC3 together with my 4 to 2 Two brothers exhaust. Not sure how much it will help mine. But when I get all that done. (within the next few weeks) I am going to do a dyno pull on it and post the results on it here.