This work describes a thermodynamic model of the exhaust and intake processes in small prechamber, three-valve, stratified charge engines. The main objective is to study the coupled effects of the prechamber orifice diameter, auxiliary-to-main chamber intake manifold pressure ratio, auxiliary valve timing, and engine speed on the air-fuel stratification between chambers at the time of ignition. The analysis highlights the important dimensionless parameters that control the engine breathing processes. In addition, the unique numerical problems of solving the governing differential equations are analyzed and discussed. Results of a parametric study indicate that the charging processes are very complex, in general. The degree of stratification at the time of ignition strongly depends on the ratio of intake manifold pressures and on the auxiliary intake valve timing, particularly for lower engine speeds (<͂2000 RPM) and/or larger orifice diameters (>͂0.3 inches).