Backpressure is considered as an obstruction on the flow of exhaust for any internal combustion (IC) engine. The level of backpressure can affect the amount of emissions and fuel consumption and the performance of the engine. Hence, the backpressure is considered a bad factor for an engine. Even though backpressure could not be eliminated completely, it could be minimized through design optimization of exhaust system. This paper shows the effects of exhaust manifold's bending radius of 115 cc spark ignition (SI) engine on low-end RPM. The aim of this study was to optimize the bending radius of exhaust manifold in order to minimize backpressure. CFD analysis was conducted to predict the backpressure of exhaust manifold samples based on design of experiment (DOE) through Taguchi's method. From the analysis result, it is observed that bending radius which is towards the outlet is the most contributing factor to the backpressure and the optimized exhaust manifold reduces backpressure by 10.5% from the existing design. The finding shows that the optimized design offers lower backpressure which could significantly reduce negative impacts to the engine's performance.
