Staright from A-Main. Check over at TruggyRacers.com...lotta guys in there run that motor.

Tuned Pipe Selection
The MR21 B01 engine works well with the Novarossi 9886 style tuned pipes, but does not work very well with OS T-2050 or T-2060 tuned pipes. The best pipe for this engine is the new MR Ninja 2053 tuned pipe which was designed specifically for this engine.