I'm with SManMTB. Anything bigger then a .21 engine is unnessisary in a buggy. You just don't have the weight or the drag in the drive tran (like the monster trucks do with those huge tires and weight) to need all of the torque that those big displacement engines have. With .21s you will get more RPMs and the RPMS tack up faster when it gets into its power band. I'm racing the sportwerks .21 right now and I can break loose all 4 tires on any terrain that I've driven on yet and it still has high RPMs. There are some good big displacement engines though that wont murder your wallet... I've raced the mach .26 for a while and I've driven quite a few sportwerks .26 engines. Both only $140 and you can still beat people running those high dollar engines around the track (not in a drag race but and engine wont help you in the corners). Any of the engines that I stated make more power then the O.S. .21 RG, they are all very easy to tune and hold it well, they last just as long as the O.S. RG, and not that much more expencive. The RG is a great engine too... there are people running them at the local track and all you need is a polish job and a JP-1 pipe and that thing will scream.