Design of mufflers is a complex function that affects back pressure, noise characteristics, emission and fuel efficiency of engine. Back pressure caused by exhaust system has negative effect on engine efficiency, resulting in decrease of power. Muffler to be design in such a way that the back pressure should be optimum and it should not disturb the subsystem operations. Hence, goal of this paper was to shorten product development cycle time through back pressure optimization. There are number of formulas for back pressure and each formula gives different result. So, to minimize the number of iteration to finalize any one of the back pressure formula, CFD analysis was performed. For validation of the back pressure theoritical formula and CFD result, simple pipe flow calculation and CFD analysis has been performed, so that at least maximum error percentage can be predict. By comparision of all three formula results with CFD analysis and experiment value have been tabulated to find error percentage. The target of the project work was to get error % of CFD and Theoretical formula to get below 15%. The minimum and the best result came for formula II that is taken up by benchmarking company’s installation guide of exhaust system for which error % was 14%. This paper gives prediction of back pressure value during its preliminary stage of design.