[shovel]

Maybe they could put some sort of a metal block into the car, with reciprocating pistons that are plumbed through a series of valves to pull in oxygen rich air and a combustible fluid of some sort (like gasoline or something) and detonate it under pressure with some type of sparking apparatus, and then use the same piston's reciprocating motion to push the spent gases out of a tube of some sort to make noise. Maybe if they did it right they could use some of the detonation's energy to turn a crank connected to the piston, and the crank could help push the car along through a gear reduction box.