2009 Audi R8 V12 TDI Concept Preview

If Audi's not careful, they could become the poster company for conspicuous consumption, automaker style.

First they bring out the R8, with its 4.8-liter V-8, then the next thing you know there's talk of a 5.0-liter...and now, straight from the Detroit Auto Show, there's bluster about a V12 TDI.

Really. At some point you have to stop, even if you can keep going. Only problem is that this particular concept is quite a bit more than a good idea, and delivers all the power of a rocket ship with plus-20 mpg.

Audi reps said quite a bit about their diesel technology, but to be honest my eyes glazed over. All they really had to say was "500 horsepower and 737 lb.-ft. of torque" followed by "R8."