I've tried EFI. Fuel is pressurized to 35psi, replace with a Taller piston head, keep the engine running at its most fuel efficient rpm and pair the motor to a cvt. an additional .6hp can be gained. If you hyper mile you can expect mpg's in excess of 1,600. Of course this isn't an option for most but if you are looking for efficiency that's your roadmap to get there.