Capabilities of DI diesel engines for passenger cars were evaluated in a research program. Three experimental DI diesel engines, a naturally aspirated 2.4L four cylinder engine and a naturally aspirated and turbocharged 1.3L three cylinder engine, were designed, built and developed. Design parameters and calibrations were determined for optimized power and fuel economy at low emission levels. The effects of cylinder displacement and turbocharging were evaluated. Vehicle tests showed that the DI diesel engine provided an 11 to 13% improvement in fuel economy relative to the IDI diesel engine. The low mileage objectives assumed for the 1985 Federal emission standards were met at vehicle test weights up to 3125 lbs.