Montana Mike, a good idea for your son would be to get a good .18 engine (SH .18 or T3.0) and also get an FM radio with servo end point adjustments such as this one: [link]http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXHBB5**&P=0[/link]. Then you could adjust how fast the truck can go with the end point adjustments, and as he becomes a better driver you can let him go faster. I think that might be more practical than buying a less powerful engine in the first place.