Extensive research is being carried out to improve the volumetric efficiency of the engine by improving port flow. Port flow characteristics plays vital role in determining the overall performance of SI engine. Higher volumetric efficiency demands the flow capacity of the ports.Steady-state flow bench testing and CFD steady flow simulation analyses are widely used promising tools in the process of port development for flow optimization. CFD port flow simulation adds cost effectiveness to the port modification process. With help of port flow information obtained from the flow bench testing, the engine power curve and system dynamics can be roughly estimated. However actual engine running is transient in behavior, i.e. the pressure difference varies widely during the whole cycle whereas the port flow testing on flow bench is steady state in nature. In the flow bench testing, the effects such as cyclic acceleration and deceleration of fuel-air column are not accounted. With the help of accurate engine simulation software, it is much more useful to use flow data to create an engine simulation model for analysis. Also one can predict the engine performance accounting widely varying pressure differences as well as the temperature effects.The present work deals with an integrated 3D-CFD and 1D simulation approach for performance optimization of a single cylinder motorcycle engine. Port flow for various valve lifts is measured for the Base cylinder head using flow bench. 3D-CFD analysis has been performed for simulating the port flow. The port modification has been done by the simulation for better flow coefficient. The port flow coefficients data from the CFD analysis is fed to the 1D engine simulation model. The effect of port flow coefficients on the volumetric efficiency, brake power, brake torque and fuel consumption is analyzed.