Nobody is going to argue that the Audi R8 diesel will be saving the earth. It won't. But, like the Tesla Roadster, a diesel version of the awe-inspiring Audi supercar could go a long way towards convincing consumers that diesels don't have to be smelly, dirty, noisy and slow. Chances are that the Audi's V12 diesel won't be making it behind the passenger compartment of the R8, but rumor has it that a 4.2 liter TDI V8 might. Yes, please ... and why not fill it up with biodiesel while we're at it.