I respectfully disagree. The internal combustion engine is only about 27 to 30% efficient. The other 70% (heat energy) goes out the tailpipe. Diesel is a bit more efficient. I must add that Shell scientists were able to get 150 mpg before 1950...in full size cars. If you're interested, watch the documentary "Gashole"
http://gasholemovie.com/index.html This underscores the relevance of the Elio concept, that's for damn sure.............