A light weight diesel engine family having high specific power output (up to 21 KW/1) has been developed for medium trucks (7/13 ton) starting from existing 6-cyl in-line N/A and T/C DI engines with a single displacement equal to 0.915 liters. To meet future U.S. federal and California emission standards changes in combustion chamber shape, swirl level, injection system and turbocarger matching have been introduced. Projections of fuel economy according to the new transient procedure proposed by EPA have been carried out. These have been compared with the projections of a conventional gasoline engine referred to the same vehicles. Finally the main relationships among the combustion parameters, fuel consumption and emissions have been explored.