This is only a semi- serious thread, since I suspect there's a simple back-of-a-napkin calculation that shows this to be infeasible. The idea is the following: a lot of a car's efficiency gets lost in the form of air drag, I.e. forcing the air to go around the car. Could one upscale a supercharger, I.e. a compressor, to consume all the incident airflow hitting the front of the car, compress it, route it through the car, and in the back expel it again? Intuitively this should reduce air drag, since a much smaller section of the car is now "visible" to the air. However, the compression and the associated own air drag might thwart the energy balance, making it negative overall. But, is that necessarily so?