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.
And the infrastructure for petroleum is very well established. Sucking it out of the ground, storage, transportation, refinement, storage, distribution, storage, etc. If you want to get really picky, you have to include the costs of maintaining the source of supply which is the Middle East for some countries and the cost of occasional spills, etc.
Petroleum has served us very well.
How a Mr Fusion and an electric motor? :)
I don't know. Maybe some chemical process that induces electricity in a coupled wire? A current produces a magnetic field — an electric motor. Again, you don't get anything for free so whatever pushes those electrons has to produce a lot of energy and it has to be controllable through some kind of a regulator. The next best thing is a storage device that drives the current in the wire and is charged from a source that is very efficient.