I just replaced my '08 exhaust with a full system from an '06 that I got off Ebay. Wow. I am still in disbelief as to just how much more low end was achieved, but I'm sure you have all heard that enough... Although this new found low end is great (if not scary at the moment), it seems as though it may have came at a price. I may be nuts, but the bike doesn't seem like it wants to rev out like it did before. I have listed the possible reasons below... Reason #1 - I'm crazy: My initial thought is that it just 'feels' like there's less on top because I am getting there so much quicker. Could it be that now that the bike is SO MUCH stronger on bottom that the top feels comparatively weak? Reason #2 - New head pipe: The '06 head pipe is not consistently round. About an inch or two after it exits the motor it flattens out quite a bit and becomes oval, with the flatter part being parallel to the ground. Then, as it starts to make the bend back, it flattens out the other way. I have never bent tubing before and I am sure there is some flattening that occurs, but this is really noticeable. It especially seems odd as it comes out of the motor as it hasn't even starting bending yet. See the pics below. The measurements shown are conversely similar with each other, where the narrow part on each measures about 36mm and the wider about 51mm. Is this normal? Reason #3 - Jetting: No idea here. To me, the bike runs great, albeit a little weak on top (maybe). I have no idea where to start or even if it's required. Anyone in the central Florida area who has done the same thing and has a good base? Seems to me the stock jetting is a 'good base' but again, I'm clueless when it comes to jetting. Long post, but any help is appreciated.