This paper describes a simple analysis for the prediction of pressure within a spark ignition engine. This is done by modelling the combustion process using the Wieb function approach, which is an exponential function in the form y = 1 -e(-axm), to calculate the rate of fuel burned. By careful selection of a and m, any spark ignition engine with any combustion chamber shape and any specified dimensions can be assessed by this model. The validity of the model has been tested by comparing the model results with those obtained from running the engine under the same operating conditions. The results obtained from the theoretical model when compared with those from the experimental ones show a good agreement. Also, the effects of the many operating conditions, such as compression ratio, engine speed, and spark timing have been studied.