The engine actually isn't that big, its about as tall as a .21, and fatter. The pictures make it look a lot bigger than it really is, most of the thing is fins. They came with AM radios, the one shown has never been started, so I have no need to swap out the radio. I would run the other one I had with the stock AM radio and have no problems, they come stock with airtronics. These little engines run great, and have a ton of power... the ignition system just drains the stock 8 cell pack pretty quickly though. This was the first RTR car to break the 60mph mark, and they do it pretty easily.