The designers of racing engines have produced engines with 3, 4 or 5 cylinders, all producing power outputs of up to 230 hp. An internal design trend within such racing engines has been observed in that the exhaust valves appear to be getting smaller and the intake valves larger, i.e., the valve size ratios (VSR) are getting ever-higher. This paper examines the logic behind this design trend by creating a mythical engine and, using both an accurate engine simulation and an analysis of the specific timeareas of the valves, determines the optimum valve size ratio for the best performance characteristics. From these analytic processes, the current design fashion to increase the VSR value is deemed to be potentially illogical. It is established that any given engine design has a value of valve size ratio which will optimise its performance characteristics either in terms of its peak power output or the performance characteristics over the usable speed range. This paper does not seek to establish a universal value for the optimum value of valve size ratio but concludes that it is different for each particular engine design and that the designer must search for it using the best-in-class engine simulation techniques. Both analytic and simulation techniques have been described in this paper. The empirical analytic technique using specific time-areas has been shown to have relevance for the determination of the optimum valve size ratio. An accurate engine simulation is shown to provide the in-depth information which can determine the optimum valve size ratio. However, the specific time-area calculations provide great insight into the formulation of the input data banks for the engine simulation process. With this insight, the designer can save much simulation time by not having to run non-relevant input data files and be more certain that the gas flow requirements during the individual periods of blowdown, pumping, ramming and the overlap periods are being satisfied.