This work is focusing on increasing the combustion efficiency of the engine by reducing the backpressure in the exhaust manifold using Computational Fluid Dynamics (CFD). CFD is the current trend on automotive field in reducing the cost effect for the analysis of various models on basis of fluid flow. CFD helps to obtain approximate computer-based solutions to governing equations for a variety of engineering problems. A CONTESSA engine of 20 hp at maximum speed of 2000rpm is taken for analysis purpose. The load and performance test is conducted. From experiment mass flow rate, temperature, velocity, pressure of exhaust is calculated and required graph is drawn. Flow through the exhaust manifold is analyzed using Fluent with temperature, pressure and velocity parameters as boundary condition. The result obtained by analysis are compared with the experimental values and found to be agreeable. By using fluent the area under back pressure is taken under consideration. Changes are done on particular area of consideration. The existing manifold is modified and the new design is analyzed. The graphs are drawn for the new design and are compared with existing manifold and results are produced. The results thus obtained are agreeable and decrease in back pressure is shown using contour and vector diagram. The result is agreeable and by comparing the existing and new design flow increase in the efficiency is found thus justified to give better efficiency.