The development and testing of the new series of Mercedes-Benz diesel engines, the Model Series 400, is discussed in this paper. The series includes 6-, 8-, 10-, and 12-cyl V-engines and 5- and 6-cyl in-line engines. All feature a 4.922 in. bore and 5.117 in. stroke, a piston displacement of 97.4 cu in. per cylinder, water cooling, and direct fuel injection.Specific items covered are the combustion system, ignition, emissions, pistons, cylinder head gaskets, and the cooling system.