The increasing degrees of turbo charging as well as the larger cylinder measurements generally involve higher demands on the design of the components forming the combustion chamber. This applies in particular to the design of the piston of large-bore two-stroke engines. The new calculation methods which are now available as well as design measures permit safe control of the higher thermal and mechanical stresses. In this connection, an important problem is the transfer of the heat absorbed by the cooling water, and this applies particularly to the piston cooling system. For this purpose, extensive tests were carried out in the authors' company, these tests involving various cooling systems using both water and oil. It was mainly an engine with a 570 mm bore and an engine with a 700 mm bore that were used for these tests. From the large number of test results, only basic findings concerning the water cooling system are to be enumerated. The test not only furnish information about the effect of splash cooling for the pistons but also indicate the significance of the individual factors. It was possible to prove that the splash effect exerts the major influence in the case of the piston cooling system, i.e. the flow velocity of the cooling water admitted to the piston is of minor importance. As the piston top temperatures only rise slowly when the flow of cooling water is interrupted, the pistons cannot be subjected to a heat shock. The second part of the paper deals with constant pressure exhaust gas turbo charging of port-controlled marine diesel engines. The operating characteristics under charging condition and emergency operation are described. The formation of the mixture during fuel injection is also dealt with and problems concerning the injection pump drive via a camshaft have received particular attention.