I just read on MSNBC,
http://www.msnbc.msn.com/id/8129979/ about a diesel car (I think by Dam-Chrysler) that was getting 70-80 MPG's. It looks ugly as sin, but developed 140 HP. The article talks more about the design of the body & chassis then it does about the motor. Still an interesting read, especially how they treat the emissions down the tail pipe.