IMHO, for 1/8th buggies the .21 is plenty of power. In fact, I would venture to say that the number of drivers that can truly handle the output of a fair-to-good .21 are few and far between. Anything larger on a 1/8th buggy is overkill, will be difficult to get good lap times with a larger engine, and is a waste of fuel. Manufacturers sell some of their RTR buggies with larger than .21 engines (i.e., .25's, .28's, .32's, etc.), but that is simply marketing hype and not really useful for the buyer.