Are you sure about your statement on turbos reducing efficiency? Some of the most economical consumer engines are turbocharged--in fact auto makers commonly cite mpgs as a reason to use turbos; so I am confused.
Yes. Turbocharging increases mpg not by increasing thermal efficiency, but by allowing to use a smaller and lighter engine. A lighter engine means less mass to accelerate, therefore less energy to spend. A smaller engine means less internal friction so less energy lost. However this theory works well if you actually don't use the full power that turbo gives you, or you use it only occasionally. These engines have great advantage in lab mpg tests, but in real dynamic driving the advantage diminishes. The main problem is that by adding a turbo, you need to decrease the compression ratio of the engine, which decreases thermal efficiency. Another thing is that turbo needs some energy to be powered, and also has some of its own energy losses. This is not free.
The new Honda Civic comes in a 1.5 turbo and a 2.0 NA, the turbo being the heavier package--but which still delivers higher mpgs. And if the turbo has more efficiency due to less internal friction, that still creates more useful energy out of the same amount of fuel, no?
You are right, but now we are not discussing thermal efficiency, but total mpg which is related, but not the same thing. Efficiency being equal, you'll get more mileage from an electric car, because it can get back some energy from regenerative breaking, and it definitely has less internal friction.
