In the automotive industry, computer simulation techniques have been developed to improve the 4-stroke engine development process. The objectives are to reduce engine development time, optimise engine performance, improve refinement, and to achieve legislative noise and emissions requirements. The application of these methods to a 4 stroke scooter engine has been evaluated. This paper describes how computer simulation techniques have been used to assist with the development of a new 125cc 2 valve 4 stroke scooter engine built by Piaggio Veicoli Europei Spa, and to evaluate an advanced 4-stroke scooter engine concept.A single dimensional fluid dynamic analysis code WAVE has been used to simulate engine performance and inlet/exhaust noise during prototype development. To support this analysis, pseudo-static valve train analysis using a multi-polynomial camshaft design approach has been used to optimise valve train performance. In addition, port development techniques have been applied to optimise the trade off between part load combustion stability and full load volumetric efficiency requirements. A potentially high specific output engine derivative based on a crankcase supercharged 4 stroke concept has also been evaluated by computer simulation.