The Edison2 Very Light Car that weighed ~830 pounds with an ICE got about 102MPGe Combined and about 129MPGe Highway.
When they put an electric drivetrain in the VLC, it weighed ~1140 pounds, and it got about 245MPGe. The VLC has a Cd of 0.160 which is critical; but obviously the most important factor is the drivetrain efficiency. Electric drivetrain is by far the best efficiency.
I think you will want to watch this video by Oliver Kuttner several times: