Lastly it does seem the best hope is for something around 30% incress in MPG.
As it has been pointed out with Fuel Vapor the legal problem is NOX.
It also has been said add a little water to the intake cools the burn and stops the NOX problem.
I guess the next question is can you still get enough bang to drive the car and how much water is need to keep up full time or match your tank of gasoline...
Personally I really look forward to the Air Car:
Compressed air car - Wikipedia, the free encyclopedia
This looks like the greatest thing ever...with up to 1000 miles on air and 10 gal of gasoline.
So why is it NOT being sold here?
Rich