Hi. I have a 2013 GS. I have fitted the BMW / Akrapovic slip on muffler. there is good schematic diagrams and fitting instructions on the Akrapovic website. I was rather disappointed in the sound, it was not a lot loader than standard with the baffle's removed ( which is just a matter of removing a screw in each baffle ). Iam an engineer, so I started looking at the system. The item in the exhaust that controls the amount of noise that the bike makes is the butterfly just before the muffler. you can see how it operates by running the bike with the muffler removed. this butterfly is only there to control noise emissions at idle. if you look at the akrapovic website, they make titanium pipes for the bike. look at the fitting instructions for fitting these pipes, they do away with the exhaust butterfly completely and also the catalytic converter. this makes no difference to the tuning of the bike as the lambda sensors are retained and the bike self adjusts.
The easiest way to make more noise, which is what I have done. is to disconnect the control cables to the exhaust butterfly ( this is quite easy, and outlined in akrapovics fitting instructions for there aftermarket pipe system ). This leaves the butterfly in the open position, because it has a spring return on it to the full open position, the servo motor still operates as usual, but there are no control wires connected.
I have also cut open my exhaust and removed the internals of the catalytic converter and rewelded. this is really unnecessary!
The result is a throaty sounding bike. not the same as a Vee twin. but you can now hear the motor at riding speed, which is what I personally like. It has done nothing to hinder the performance of the bike, Akrapovic claims torque increasese, but I think these are small and maybe unnoticeable, as the engine / bike pulls like a train anyway.
Last edited by kiwi rob; 15-Sep-2014 at 05:49 PM (951).