1. ABSTRACTThe techniques harmonizing the contradiction which consists of exhaust noise reduction and engine power increase, have been required for the exhaust muffler. This techniques rapidly improved by means of the clarification due to the acoustic theories and the flow analyses. Recently, according to the passenger car tendency toward high grade and high performance, demands for low noise and high power exhaust systems are increasing year by year.The “Dual Mode Muffler” system (abbreviated, below, DMM) mounted on Nissan Cedric, Grolia and Cima series, installed in 1987, is achieved the consistent of the quietness and the engine power performance. This system is the first control type exhaust system for the 4 wheel car.On previous paper, the analyses of acoustic characteristics on DMM were mainly shown. The analyses of exhaust pressure characteristics are also an important theory along with the acoustic in the development of the exhaust system. This paper intensively describes these analyses to reduce the engine power loss.