I found a video of an Opel Speedster that someone converted to diesel.
Here are the specs:
0-62 mph in 5.9 seconds
137 mph top speed
41.2 mpg fuel economy
2.2L 4 cylinder turbodiesel from an Opel Vectra
160 horsepower
235 lb-ft torque
2082 lbs weight
0.38 drag coefficient
16.8 sq ft frontal area
49,000 Euro price tag
It doesn't perform nearly as admirably as the Eco speedster concept, which demonstrates just how much weight, rolling resistance, aerodynamics, gearing, and reduction of engine displacement can all add up in improving fuel economy. As it is though, the above car in the video is still quite nice!
I wonder how an aeromodded Triumph Spitfire would do with an OM603 MB diesel with a Myna performance kit and modified gearing... *drool*
I just can't get the idea of an 80+ mpg, 0-60 mph < 4 second, 200+ mph capable eco car out of my head. It's definately possible.