Remember, most people are running the Ninja as a Motor and pipe combo. ie. Ninja motor and Ninja pipe... This should extract the most power from that motor. The OS TZ, when match with the correct pipe and header can run with and beat the Ninja in the proper hands. Don't get me wrong, the Ninja is a very nice motor, but so is the OS when geared correctly and matched with the correct pipe and header to take advantage of it's low and midrange power and torque... The Ninja pulls nicely and has very good top end. Mugen has a very Nice Motor in the Ninja!!! The OS is a good motor as well, it has more power down low/midrange then the Ninja and top end can increase when setup correctly. You can't go wrong with either one. Buy the motor which best suits the track you run on...

RC_Alan