A prediction model of the performance and emission characteristics of an axisymmetric spark ignition engine has been developed.The chamber is considered to be a thermodynamic system. Combustion is computed using the Blizard and Keck eddy entrainment mechanism as modified by Tabaczynski et al. Heat Transfer is computed by the forced convection equation and a gas motion model based on continuity equations. Changes in the geometrical shape of the chamber and flame propagation have both been taken into account. NO formation has been modeled with the extended Zeldovich mechanism.Model predictions and literature data were compared. Appropriate values were determined for the four parameters describing the combustion process and the agreement was good. Parametric studies on both performance and emissions were then made. However the experimental data available is insufficient to test the model fully.A more complete comparison will be made as soon as the Department test engine is ready.