It's not possible to use any part of the CBR600RR exhaust system, or that of any other 4-stroke, as the "workings" of the two types of system are completely different.

There are, as of yet, no aftermarket under-seat exhaust systems for the NSR.

The main problem with bringing an exhaust up under the seat is the routing of the pipe. The 2-stroke expansion chamber shape and length are critical to peak performance and it's just not practical to chop and change what works perfectly for something that just looks good!

The idea has been looked at before though. Matt from TYGA Performance and I looked closely at the possibility of turning one cylinder 180º, but the exhaust manifold then runs straight into the crankcase! There is just no way to make it work. The only other way I could think of doing it was to modify a CR125 pipe (or similar) and routing the exhaust in behind the fairing like a Yamaha TDR250, but the MX bikes have a completely different chamber size and shape for totally different power output characteristics! Put simply, it ain't never gonna' happen!!!! :)

Andy.
NSR-WORLD.COM