Unless he has changed the engine, even a standard RST would hand him his arse.

Agree to the bet, and insist you both give the 100 pounds to a third party to hold onto.

Just to make sure you dont fluff the start and lose out when you should have won, make it so you both spend the day at the pod and whoever gets the best time wins, as your car is likely to be less consistant that his, so more goes is in your favour.