2009 Audi R8 TDI
 

Car & Driver puts some thought into what a TDI version of the R8 sportscar might be like and comes to the conclusion that only the 4.2-liter V8 TDI engine would work...

Of course that's assuming Audi doesn't have another brand new engine in development.<ul><li><a href="http://www.caranddriver.com/carnews/13108/2009-audi-r8-tdi.html">http://www.caranddriver.com/carnews/13108/2009-audi-r8-tdi.html</a</li></ul>

Any info that you have on such an engine?

No I don't have anything specific
 

Obviously I've asked repeatedly. I know for certain that the 12 is TOO HEAVY, but not much else.