The development of a computer simulation model for an automotive turbocharged multi cylinder spark ignition engine for gasoline and methanol operations is described in this paper. The model illustrates the simulation of the thermodynamic cycle comprising of compression, combustion, expansion, exhaust and intake processes. The scheme employed for matching the turbocharger and engine is also highlighted. The computed data of the above model is validated with the available experimental data. The model predicts the brake power developed by the engine, brake specific energy consumption, the nitrogen oxide and carbon monoxide emissions for both the gasoline and methanol operations, corresponding to the original and improved manifold design configurations. The overall analysis of the results show an increase in power output, lower nitrogen oxide and carbon monoxide emissions and improved brake specific energy consumption for the methanol fueled engine as compared to the gasoline version for both the original and modified engine designs operating on naturally aspirated and turbocharged conditions.