The present review paper is on the performance improvement of IC engine by using backpressure reduction in the exhaust manifold and their CFD analysis of Single Cylinder Four Stroke C.I. Engine. It is found that development of energy-efficient exhaust manifold system is possible by minimization of backpressure on the engine, due to an increase in brake thermal efficiency. Effective utilization of energy from exhaust manifold can be achieved by designing for backpressure reduction by energy-efficient exhaust manifold system. The exhaust manifold system design with reduced back pressure requirements is an important factor for upgrading engine performance. It is analysis by CFD on reduction in the backpressure of the exhaust manifold system to increase the efficiency.