With the growth of average effective pressure in cylinders of marine lowspeed diesel engines the requirements increased to materials used for manufacturing their critical parts. This paper reports the dynamics of mechanical data changes in materials (steel and cast iron) of critical parts in diesel engines by the example of produce of the Bryansk engineering plant. From 1961 till 2008 the Bryansk engineering plant is the only manufacturer of powerful marine low-speed diesel engines in Russia. Diesel engines were being built under licence of “MAN Burmeister Diesel” Co. Diesel engines manufactures in different years differ with forcing degree. A diesel engine with a higher forcing degree has a higher value of mean effective pressure. In the paper there are shown types of diesel engines manufactured by the Bryansk engineering plant and is shown the evolution of mechanical data of cylinder iron bushes, piston rings, steel components of a bed frame, crankshafts. It is pointed out that the application of new steel and cast iron kinds should follow considerable changes in the design of marine low-speed diesel engines of the type 6DKRN 50/200-14 of compact modification. The conclusion is drawn of that with the growth of a forcing degree in diesel engines the mechanical data of steel and cast iron will increase at the expense of material chemistry changes by means of the introduction of alloying elements and application of modern metallurgical equipment for qualitative billet manufacturing.