I just raced on Friday night with the Orion 13.5 in my Mamba Max and other than a slight hesitation on the initial hit of the throttle one time (in my start up of my warmup lap) it worked flawlessly all night long. Geared 42/116 in my MI3.
You can watch my car from the race Friday night. THe first touring car race they show is the B main. 2nd part of the vid is me TQ with the bright DNA body. I'm running 13.5 Orion with my Mamba Max with 4200's vs all other cars in the main have 13.5 with lipos. You will see my car has zero problems running the Orion 13.5 motor.
http://www.altoonaraceway.com/RaceCoverage110207.html Click on touring car mains to see the vid.