[olmon]

Heated & vaporized fuel was the principle behind the 'miracle' carbs that would give you 100mpg+ on an American V8 in the 60s. They did work, however, after a few thousand miles, the valves were gone. So much for saving money. There have been several forays in that area over the years, but no real news. Smokey Yunick, of racing fame, modified a Pontiac Fiero with the 4-tech, called it a 'heat' engine. I only saw one article on it where he claimed much increased efficiency along with greatly increased power (to the point that he had to beef up the drive axles to handle it). Apparently he got bought out by the oil companies because that one article was all I ever saw and have never been able to find any more information or eve nreferences to it.
Also, in the 70s, Pratt & Whitney developed an engine for the military, a twin rotor, stratified charge, turbo-charged, multi fuel rotary engine that produced approx 700 hp on pump gas and (in a 2ton truck crusing @ 60mph) gave 35mpg. Another thing that you won't find any reference to. It was classified, I just happened to see the R&D papers on it @ the shop I was working in at the time.
In 1974, a hydrostatic drive system was patented by a man in Portland that, powered by an 18hp lawn tractor engine, gave 75 mpg @ 60mph. A modern version of that system, using a free-piston 2cyl diesel to pump, with regenerative braking, gives 0-60 @-5 sec and 130+mpg in a 5 passenger vehicle in the Honda Accord size range. There is a good website describing this auto & its' drive system. Look up Valentin Technologies & XPrize cars.