O.S. RG is the best motor you can get for $110. Very easy to tune and decent power 1.9hp at 30,000rpm. I would sujest something more like a sportwerks .26 though. For $140 your getting 2.75hp (I forgot at what RPM). The motor doesn't have a lot of bottom end but if you put on a JP-1 pipe that solves it. It has enough power and RPM to push the mayhem it comes in officially to 50mph and you need speed for bashing or whats the fun of it? With the O.S. RG you'd max out at 40mph... and 45mph if you gear it high and you really just wont have the same punch the SW .26 has.

If you wanted to spend more money I would say buy the RB Concept S7.

Whatever motor you get it needs to have a solid backplate thats flush with the crankcase on the motor. If you have a pull start or roto start the backplate used for them will hit the chassis not letting the motor meet its mounts.