1. AbstractMercedes-Benz have developed their 4, 5 and 6-cylinder Series 300 and 400 diesel engines for the U.S. and Mexican truck markets. These direct injection and air-to-air charge air cooled engines are of low weight and offer the high power-to-size ratio required for modern truck applications.The paper presents an overview of legal regulations in the countries where the engines will be offered and highlights technology needed to meet 1991 U.S. emission limits. It deals with the tuning of the combustion processs, adaptation of injection and turbocharging systems and design of the injection timing system. The new Mercedes-Benz flame heater systems help to further optimize running characteristics of a cold engine in order to meet environmental criteria during starting, warm up and in the running mode. Designing for future, more stringent emission requirements are also discussed.The new engine being introduced is the in-line Mercedes-Benz OM 366 LA. Other engines discussed will be introduced at a later date.