find the most efficient motor possible(gas or electric) and put it/them(if more than one is desired) onto the lightest, stiffest chassis possible.
Then make a body to go over it with a cockpit of some sort.
I might lean towards a magmotor of some sort or possibly one of these-
http://robotcombat.com/marketplace_motors_perm.html
if you feel like going for an overkill solution.
Perm-132
72 V Performance
Peak efficiency: 88.6%
Peak power:*34.3hp
No-load angular velocity:* 3590 r/min
Stall current:* 1440A
Stall torque:*38500ozf·in
Oh, and find some FM radio gear with good range
Edit for random thought- Perhaps a flywheel based design would be worth considering. Spinning a 20-30lb flywheel to oh, say, 500mph(yes, insane, I agree) then transfering the power to some wheels and seeing what it does could be interesting.
Things to consider-
Wheelie bars
Very Low CG
front/4wd
how long it'll take a small motor to spin something that weighs 30lbs to 500mph