The design and operational variables of exhaust systems are decisive to determine overall engine performance. The best engine overall performance can be obtained by proper design of the engine exhaust systems. Using this engine model, the effects of the parameters of the exhaust systems on the engine performance are obtained. In particular, the following parameters are chosen: diameter of the exhaust manifold, exhaust pipe lengths, and geometry of pipe junctions. This investigation helps to find the optimized size of exhaust pipe system which can be used further designing as well as the manufacturing of exhaust manifold.