Fuel economy and emission characteristics of two light-duty diesel-powered vehicles, representing 3,500-lb and 5,500-lb passenger cars, were determined and compared to those of similar 1975 model year gasoline-powered vehicles. The diesel-powered and gasoline-powered vehicles were designed to have comparable acceleration performance.The 3,500-lb vehicle with a 247 cubic-inch-displacement (CID) diesel engine and the 5,500-lb vehicle with a 636-CID diesel engine gave respectively, 43% and 33% better combined city/highway fuel economy than similar vehicles with 250-CID and 440-CID 1975 model year gasoline engines. In the 3,500-lb vehicle, emissions both from the diesel and gasoline engine were below the 1976 Federal emission standard. Emissions from the 5,500-lb vehicle both with the diesel and with the gasoline engine exceeded the 1976 standard. The potential for meeting standards more stringent than those for 1976 was not investigated for either gasoline or diesel-powered versions.Additional work was done with a 3,500-lb vehicle (198-CID diesel) and a 247-CID diesel engine mounted on a dynamometer stand using turbocharging, combined supercharging/turbocharging and varied engine-to-vehicle speed ratio as experimental variables. The results in terms of fuel economy, emissions, and vehicle performance are discussed.