Don, I'm ex-tech and an engine development engineer (part-time). My specialisms are oily bits but these days with a heavy leaning to mainly induction and exhaust. I help develop road bike engines and car engines. On these modern road bikes changing the exhaust by cutting up the standard pipe can be detrimental to the performance and economy of the bike. The internal twists and turns in the exhaust system, as you will no doubt know are designed to give the right flow rate over a wide range of throttle, rpm, and load settings, and induce the correct back pressure for the widest range of speed and load ratings. Once you mess with the back pressure you may be disappointed with what you get. Gone are the days when just switching exhausts would make little difference or actually make a positive difference to a road machine. The bikes have to come optimally tuned and there is little the owner can do to improve things for road use. Remember, I'm talking about road use. Racing is something else altogether, as you will again know. However, I've not done that to a Burgman 650 and no one I know has done it. So if you do, let us all know how it goes. Good luck.
