George is right, look for a good off road .21 motor. I had a Technokit SPRY Rally Game car several years ago and had and O.S. .21 VZB in it. That motor had plenty of torque and top end speed. I think there is and O.S. .21 VZB V-Spec which is now available. I believe it's hand modified but I may be wrong. You should check to see what the hot motor is that all the off-road guys are running nowadays.

Regards,
Speyederjedi