He said he redesinged the engine using a desing his father came up with 60 years ago. I am sure if this is real the engine looks nothing like a stock mustange engine, I've searched and it seems alot of people get high milage using a diesel hybrid engine with a turbo.
here is the news story for the mustang
http://video.wnbc.com/player/?id=271843
There you go, proof it is possible Guinness World Record for fuel economy at 103.7 mpg! And I believe it was done 23years ago, think what we could do today.
http://www.100mpgplus.com/pr/avion_20070814.html
Here is the xprize info
http://www.edmunds.com/advice/altern...3/article.html