The dissertation above is outstanding. As a mechanical engineer, motorhead, former employee of GM, and now working in commercial power industry, I am familiar with just about every concept presented.
The only thing I didn't see that I think is important in this context is (hoo boy, I hope I can remember this one correctly) the Carnot efficiency. A scientist named Carnot did a great deal of research into thermodynamics. He proved that the most efficiency one can obtain from a thermal cycle (and that means gasoline or diesel engine, a steam turbine, a Stirling engine, etc) has to do with the ratio of the hottest to coldest temperatures that cycle operates between. Given the temperature-limited structural properties of modern materials, the most any heat engine can accomplish is a little better than 30% efficiency. If you look at the latent energy in a gallon of gas, take one third of that, and compare that to the power required to propel a car of nominal weight at 60 mph, you will see quickly that 200 mpg really is almost impossible. All the stories of the '70 about the "200 mpg carburetors" are myths, IMNSHO, ESPECIALLY given the weight and (abysmal) aerodynamic of cars of that era.