Newtonian Physics is what determines gas mileage.The higher the MPG, the lower the Curb Weight of the vehicle.
My 6000 lb Chevy truck gets 13-14 mpg,and my 3100 lb Chevy car gets 25-28mpg.
My parents' 1970 Opel station wagon got 28mpg,it probably weighed less than 3000 lbs.
All this tinkering with fuel systems can squeeze out a few more points of efficiency at ever-increasing costs per percentage pointb but the laws of physics can't be changed by any government .Not even one lead by the Kenyan impostor.