The thermodynamic process of an internal combustion engine is notoriously inefficient ~ 20%. Diesel engines are slightly more efficient. And that doesn’t include the drive train.
I suspect that an electric motor is a lot more efficient.
Of course, when figuring efficiency a person has to include EVERYTHING!
Well, since we seem to be afloat in oil and NG, and with GTL fuels right around the corner, I doubt that efficiency is an immediate concern. Any ICE blows the doors off the efficiency of a lead/acid battery, when time is factored in.
Diesel engines are slightly more efficient.
OK, make it a .5L turbo diesel.
when figuring efficiency a person has to include EVERYTHING!
Well, you could throw a few thermocouples in the exhaust stream and extract a few more watts... or maybe run a heat engine with its own generator.