You could ride with no muffler at all on the R3 and the ECU would not know the difference; the catalytic converter on this bike is also the muffler box. Yamaha knew the 12-pound factory muffler would be going away on most owner's bikes, so they designed the system for aftermarket slip-ons to be easy to install (as in, they did not weld the muffler to the midpipe). I put a "Devil Evolution" muffler on mine this week after a few "no muffler" rides, and the only difference is the better sound the can makes and the weight savings over the factory unit. The engine ran the same with the factory muffler, no muffler, and with the new one. The only time you would need to worry about the ECU is if you replace the whole system.