A computer simulation of the four-stroke spark-ignition engine cycle has been used to examine the effects of turbocharging and reduced heat transfer on engine performance, efficiency and NOx emissions. The simulation computes the flows into and out of the engine, calculates the changes in thermodynamic properties and composition of the unburned and burned gas mixtures within the cylinder through the engine cycle due to work, heat and mass transfers, and follows the kinetics of NO formation and decomposition in the burned gas. The combustion process is specified as an input to the program through use of a normalized rate of mass burning profile. From this information, the simulation computes engine power, fuel consumption and NOx emissions.Wide-open-trottle predictions made with the simulation were compared with experimental data from a 5.7ℓ naturally-aspirated and a 3.8ℓ turbocharged production engine. The predicted trends of mean effective pressure and fuel consumption showed acceptable agreement with the data.Simulation studies were performed to compare the fuel consumption and NOx emissions of a 5.7ℓ naturally aspirated engine with a 3.8ℓ turbocharged engine over the complete load and speed range. These engines have equal maximum power. Further studies were carried out to examine the effects of reduced heat transfer on engine performance, efficiency and NOx emissions. Reductions in heat transfer were simulated by increasing the thermal boundary layer resistance, and through the use of ceramic materials on selected engine components over a range of combustion chamber wall temperatures.