Just ran across an article about a mechanic in Ohio that created an engine (or converted some other engine) in his 1987 Ford Mustang that gets 110 MPG but puts out 400 HP and 500 ft./lbs. of torque. Other measurables include a 3 second 0-60 MPH and a top speed of 180 MPH.
Not that everyone needs a car of this capability, but clearly the potential could be massive. Apparently the guy is a bit hush-hush about what is exactly going on under the hood (he's getting patents, entering X-Prize competition, etc.), but it has apparently been verified by a third-party.
Read the article here.
Like one of the comments, I agree he should have used a Mustang 20 years older or 20 years newer -- 1987 = blech.