Summary: The currently used semiactive-type muffler determines its opening valve time depending on the components of the variable valve. In this study, a device that can conduct the exhaust is manufactured and experimented. To analyze the detailed factors in this study, commercial software, ANSYS (CFX), was used to conduct the floating analysis. Through the experimental and analysis results, the pressure drop in the exhaust gas and velocity distribution characteristics were analyzed. Design factors that can reduce the exhaust gas pressure in the engine were proposed on the basis of the analysis result. The maximum flow of the mass-produced muffler-copied orifice was limited to below approximately 15g/s owing to the increase in the pressure drop. The muffler with variable valves has no flow limitation owing to the pressure drop within the experiment range. On the basis of the same flow amount of 15g/s, the pressure drop in the muffler with variable valves was 40% of the pressure drop in the muffler-copied orifice, which is an excellent result. The reduction in the pressure drop can reduce the emission resistance of the exhaust gas in the engine as well as help improve the volumetric efficiency of the suction air and engine torque.