Hi here are my thoughts on fitting an after market exhaust. The main reasons seem to be lighter wieght and sound. Personaly I want equal or more power and better sound. All standard exhausts are tuned to the engine but are all after market cans? I doubt it. An exhaust needs its first baffal plate to be at a set distance from the exhaust port which determines were the engine developes its power. Consider a two stroke the fuel air mixture passes through the engine and into the exhaust BEFORE ignition and is rammed back in by the rebound pulse from the baffal plate which has a specific sized hole which allows most but not all the exhaust gas to escape. The gas that cant get thro the hole piles up against the plate and bounces back up the pipe in effect super charging the engine. High performance four strokes use this system also. As the XT660 pops and bangs on the over run there must be some fuel air mixture in the exhaust and the above system must be in use. If I decided to fit an after market exhaust my first question would be has the exhaust been tuned to the bike on a dyno and where in the rev range has the HP and torque been increased. A louder exhaust could well be a too lean power robbing exhaust. This is not just a theory of mine I once designed an expansion chamber for a suzuki GT550 after studying gas flow through flat plate orifices at college during my engineering apprentice ship. I hope the info is of some use and food for thought.

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XTz 660 tenere, adventure spec bash plate, main stand, skid marks tall screen, Oxford tail pack 36 litre. Kobra hand guards, Bigger cast footpegs, Zen overland luggage plate, USB power point, iridium spark plug, TKC80 f k60 R tyres, o2 and fuel Kev mods, DNA stage 2 filter. bark buster bar wieghts, Touratec side stand base and GPS mount. Led spot lights