I would hazard a guess that you are trying to create an E30 with world record fuel economy. Front wheel drive cars are generally better because there is less rotating mass between the engine and wheels sucking up kinetic energy, so if you were to take a 325iX and remove darn near everything that transmits power to the rear wheels, you could possibly see some gains. Otherwise, a RWD E30 with a really light flywheel would also help. Contrary to popular belief, the "losses" in efficiency in RWD cars are not from friction, but rather parasitic leeching of energy into rotating more components rather than forward kinetic energy.