I put this pipe on my Crf450 and it dramatically improved the throttle response, and totally eliminated flameouts/pop stalls.
Yoshimura R&D has developed an evolutionary new exhaust system for the exciting Honda CRF450R. The all-new Yoshimura RS-4 was designed after extensive testing and the results are profound. Yoshimura has been the official exhaust supplier to Team Honda Red Bull Racing for several years now. All of that experience has helped Yoshimura in making an exhaust that compliments an already great bike. The RS-4 not only increases power and is light, but it also has a lower centralized mass coefficient to provide better handling.