[dcb]

imagine, you have a small car, i.e. civic sized.

and you have a couple, say 400cc motorcycle sized engines under the hood, complete with transmissions and clutches/etc. And they are tuned for efficiency (feedback/fuel injected/etc).

Each engine drives one wheel. They are only connected through the ground.

You can put the engines side by side in back and make it rwd if you like, whatever. Ladder bars and dual chain drive might be easier to visualize anyway, assume you have the drivetrain sorted (and cooling and exhaust and shifting and charging and everything). Assume the layout works for purposes of this discussion, and you can live with the acceleration both engines provide.

One engine is sized just so that it is very close to bsfc peak on your normal hiway excursion, or wherever you cruise.

The other engine is the same size.

You can engage/disengage/restart them independently.

You can (should) use both when accelerating/climbing, and use one when cruising, and none when coasting of course.

Bonus, if one fails you can probably limp home on the other one, even if it means removing a master link with your pocket knife.

If you went all aerocivic on the body and optimized the engine size and gearing for best bsfc cruise, what kind of city/hiway mpg do you think would be possible?

Has this been attempted?