A quasi-dimensional computer simulation of the turbocharged spark-ignition engine has been developed in order to study system performance as various design parameters and operating conditions are varied. The simulation is of the “filling and emptying” type. Quasi-steady flow models of the compressor, intercooler, manifolds, turbine, wastegate, and ducting are coupled with a multi-cylinder engine model where each cylinder undergoes the same thermodynamic cycle. A turbulent entrainment model of the combustion process is used, thus allowing for studies of the effects of various combustion chamber shapes and turbulence parameters on cylinder pressure, temperature, NOx emissions and overall engine performance. Valve open areas are determined either based on user supplied valve lift data or using polydyne-generated cam profiles which allow for variable valve timing studies. A detailed friction model is used which predicts rubbing losses from the crankshaft, reciprocating and valvetrain components and auxiliary losses from engine accessories. The simulation has been calibrated and validated against experimental data from a 1.1 liter engine. It has been shown that the model is capable of predicting combustion process parameters as well as total system performance over the entire operating range. Further, to demonstrate the utility of the simulation, a series of matching calculations has been carried out for a new 1.4 liter engine. The benefits of using a 4-valve, fast burn combustion chamber design on high-speed performance have been demonstrated. Operation of the 4-valve engine with only one of the intake valves active has also been investigated as a strategy for increasing low speed torque.