LOTS of Engines to choose from...probably the best deal going right now is the Megatech .16 rated at 1HP for around $100 and a Guy came into the Shop i work PT in the other day and had a plain 'ol OS.15 CV (~.56hp) in his jerking the front tires off the ground for reliability go with the OS .15CV or .15CV-R (1.1hp) if the OS isn't in your budget go with the Megatech by all means, in either case you will see a huge improvement if the motor is properly tuned