Depends how far he wants to overdrive it. 8hp is enough to keep a lightweight car moving at 'around town' speeds, but he's not going at highway speeds for very long unless he's got amazing cooling.
I agree, don't put it in anything larger than a lawnmower or bike....a person i work with is putting an advanced dc 8hp-ish motor in his escort. its not going to move with that in there is it? the reason i ask is because i have one but would never consider putting it in anything but a bike..................