Might as well just make an engine that works on water. What if you run out of "gaz" and don't feel like peeing? You're screwed. You gotta drink water and wait until it goes through your system.
You know those long road trips were you got to piss really bad, but have no good place to pull over and piss? Problem solved! Pull a hose out from under the drivers seat and piss right into the fuel tank. Awsome! Also, I workout a lot so I drink about 4 lt. of water a day. As a result I piss a lot, so I guess I could open my very own fueling station.
This would seriously rock if you could get a system designed that could work with both water OR piss. Piss of course being the optimal fuel source requiring far less voltage.
I can just see it now when you're driving down the highway. Every so often on the side of the road you see a guy with his pants around his ankles with his crotch pressed against the side of the car.
"Just needs some fuel buddy!"
This begs the question though; how would women drivers refuel? (something tells me I don't want a response to that...)