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The performance of two-stroke, high specific output engines, is influenced considerably by the ignition timing curve. This paper describes the cylinder pressure analysis of a TZ250B Yamaha racing motorcycle engine. Cylinder pressure data was recorded for compression ratios of 7.8 and 9.0, for a range of engine speeds. The analysis of the cylinder pressure was carried out with computer software written in fortran 77 code.

Coefficient of discharge for a particular flow discontinuity is defined as the ratio of actual discharge to ideal discharge. In an engine environment, ideal discharge considers an ideal gas and the process to be free from friction, surface tension, etc. Discharge coefficients are widely used to monitor the flow efficiency through various engine components and are quite useful in improving the performance of these components. In modelling the flow through internal combustion engines it is equally important to have accurate values for coefficients of discharge through the combinations of valves, ports and ducts. It is especially important when modelling high performance two-stroke engines, due to the relatively high flow rates and the rapidly changing flow directions. Such an engine relies on the plugging pulse from the tuned exhaust system to ram escaped fresh charge back into the cylinder, prior to exhaust port closure.