The matching of an engine and its supercharger, have large effects not only on engine performances, and gas flow, but also on the quantity of the trapping air and the blow by air. These quantities control thermal loads in combustion chamber walls, which is a serious problem at present. In order to grasp quantitatve relations, we carried out a series of systematical tests on the matching between the engine and its supercharger. The tests were carried out with a two cycle diesel engine, having a large cylinder bore. Turbine nozzle area, diffuser inner diameter and scavenging air temperature were changed systematically as they were easily chosen in the supercharging system with an air cooler. By these tests we investigated the cycle factors such as the trapping air quantity, the blow by air quantity, and more over, engine performances, the gas flow. Analyses of the results gave us standards of the items previously mentioned. Further, when the blower and the air cooler are stained by secular changes, the matching condition is spoiled, and the suction air quantities are decreased. Assuming such conditions, tests were carried out by discharging a part of the scavenging air to atmosphere. On analyses we got standards for such conditions. Adopting a supercharging system found to be the best by the previous tests, we carried out two more tests : fuel injection timing and opperation using low quality heavy oil (C heavy oil) . The results of these tests were numerically analysed and given in this paper.