Back in the late '70s, a couple entrepreneurs in Florida put a small marine diesel engine into a Ford Maverick. They turbo-charged it to the hilt and claimed 84 mpg at 35 mph. When they ordered 10,000 Mavericks without engines from Ford, the EPA shut them down. Too much pollution. Does anybody know where to find these guys?

A site with something reasonable is...
http://www.treehugger.com/files/2008/10/2008-ald-fleet-world-mpg-marathon-toyota-yaris-diesel-aygo.php