Currently improving the environmental performance of reciprocating engines is an urgent task in the development of engine building. The results of the modernization of the diesel engine (21/21 dimension) by applying the Miller’s cycle are considered in the article. The valve timing diagrams for the basic diesel and the Miller’s cycle diesel are shown in the article. The comparative emissions chart and graphs of specific fuel consumption were obtained on the basis of tests. It was found that the NOx reduction is 16 %, the CO reduction is 50 %, the CH reduction is 54 % when the Miller’s cycle is applied. At the same time, a decrease in the specific fuel consumption is observed up to 4.6 %.