This paper outlines some developments in engine modelling techniques and details the results of an extensive validation exercise. This validation was conducted in two distinct parts: firstly, on a specially constructed rig, and, secondly, using engine test results. The test rig described was constructed in such a way as to rigourously test the theories employed. Comparisons were made between measured and predicted pressure traces and air mass flow. The predicted results are shown to be in good agreement with all measurements recorded. The performance of a complete engine simulation is also described and compared with actual dynamometer test results. The accuracy of this model is clearly demonstrated for all engine performance parameters.