I just put this pipe on my bike,the stock jet is a 162 I believe,I bought a dynojet off of ebay for it($50.00) the kit comes with all the different size jets so you can test and tune,the instructions for mine said to use a 170 at my elevation(georgia- below 3000ft)Just took it to windrock this past weekend,felt a slight difference in the elevation changes,but the bike is really alive now.Highly recommend getting a dj kit and the mudslinger,it's got a good sound but not as obnoxiously loud as some of the hmf's out there.