A comprehensive general purpose engine simulation model has been successfully developed. This paper reports on an investigation undertaken to compare the accuracy and computational efficiency of four alternative methods for modelling the gas flow and performance in internal combustion engines. The comparison is based on the filling-and-emptying method, the acoustic method, the Lax-Wendroff two-stage difference method and the Harten-Lax-Leer upstream method, using a unified treatment for the boundary conditions.The filling-and-emptying method is the quickest method among these four methods, giving performance predictions with reasonably good accuracy, and is suitable for simulating engines using not highly tuned gas exchange systems.Based on the linearized Euler equations, the acoustic method is capable of describing time-varying pressure distributions along a pipe. This method is the fastest approach to obtain pressure wave forms, indicating the condition where the resonance occurs in the gas exchange system. However, this method generally overpredicts the volumetric efficiency.Based on the full Euler equations, the Lax-Wendroff two-stage difference method can predict the behaviour of finite amplitude waves in the inlet and exhaust manifolds with good accuracy, but requires the flux-corrected transport technique to avoid non-physical overshoots near discontinuities. This method is the slowest among the four methods compared.Compared with the Lax-Wendroff method, the Harten-Lax-Leer upstream method improves the prediction accuracy and computational efficiency without non-physical overshoots, and is suitable for detailed analysis of engine gas exchange systems. The Harten-Lax-Leer method can be used to replace the Lax-Wendroff method.