Previously, the main purpose of a vehicle exhaust system was to reduce the exhaust emissions and noise caused by a running vehicle. However, customers nowadays tend to value running performance, exhaust noise quality, and silence, which are believed to maximize driving pleasure. As vehicle exhaust systems are being tested and improved in various ways to satisfy customer requirements, technology is advancing rapidly. A great challenge in the design of an exhaust system is maximizing performance by quickly discharging exhaust gases at an optimal back pressure from the exhaust pipe while reducing noise and vibration simultaneously. For vehicles with a naturally aspirated engine, the exhaust pressure at a low speed RPM is very important, because the valve overlap of the engine occurs when the intake valves start to open near TDC(Top Dead Center) before the exhaust valves are completely closed. When the engine idles or rotates at a low speed, a low pressure is generated in the intake manifold and some exhaust gas flows back due to a differential pressure during the valve overlap period. Accordingly, the exhaust gas flows back into the cylinder together with air and fuel. The backflow of exhaust gas is greatest at a low engine speed. Moreover, the unstable engine speed at a low RPM or during idling generates noise and vibration, which may cause discomfort to the driver. Recently, variable valve systems such as VVT(Variable Valve Timing) have been used to continuously control the angle of camshaft. In this manner, the operation of the valves is controlled and the valve overlap is minimized. However, the backflow of exhaust gas still occurs. In addition, owing to emission regulations and rising oil prices, the technology is continuously developed to make vehicles run at a lower RPM for fuel economy. When a low back pressure is generated during idling or low-speed running, the engine speed becomes unstable and the irregular excitation force of the engine causes a booming noise and resonance. Manufacturers have attempted to address this complex issue encompassing engine output, fuel economy, and noise/vibration by designing an optimal exhaust system. The exhaust system must be designed to maximize engine efficiency while reducing exhaust pressure, effectively decreasing noise. In other words, each exhaust system must perform two seemingly incompatible functions simultaneously. The objective of this study is to propose an optimal shape of an exhaust system for sports sedans with a V6 and above engine. To achieve this, an experiment was conducted as follows. Before a prototype was fabricated, an exhaust system was designed and the fluid flow was analyzed. A pressure transducer was installed in the prototype, and the exhaust pressures on the exhaust system were measured at low, medium, and high engine speeds. Noise and vibration were also measured to analyze the impact of junction shape on the silence of vehicle. Exhaust emissions were measured to identify the amount of hazardous air pollutants. Finally, wheel horsepower, torque from wheels, noise, and vibration were analyzed using a chassis dynamometer to identify an output difference according to junction shapes and propose an optimal shape. In addition, a variable device was applied to the exhaust system with an optimal shape for improved quietness. As a result, the vibration on the vehicle body was reduced by 2.45% in the Y-axis and 5.75% in the Z-axis.