New 6 cylinder direct injection 11 liter diesel engines which have naturally aspirated, turbocharged, and turbocharged-aftercooled versions have been developed and moved in production at the end of 1983. The highest output of the turbocharged-aftercooled version is 276 kW (375 ps) at 2200 rpm. Based on Komatsu new technologies 125 mm bore diesel has been designed to meet the users' demands, such as compact in size, light in weight, extremely high performance, high reliability and durability. The turbocharged and turbocharged-aftercooled engines are characterized by the adoption of the ductile cast iron piston which is the first application into the high speed, four cycle diesels in production in the world, and which was enabled by Komatsu design and precision casting technologies. This paper also covers the other design aspects and performance characteristics.