Studies have, by calculation, shown that fast combustion rates tend to produce low NOx levels. Their analysis has been partially confirmed by actual engine data on a highly turbulent fast burn engine. Thus, an experimental program was conducted to develop quantitative data on the effect of some of the engine design features that are known to have a significant influence on combustion rate.The effect of five engine design factors on combustion rate was determined. Burn time was measured on 17 different engine configurations, each configuration containing different design levels of the five design factors. Burn time measurement was also made on a carbureted highly turbulent bowl-in-piston fast burn engine with a centrally located spark plug. Significant reduction in burn time from a production combustion chamber was achieved by application of the design factors, but the fast burn rates of the carbureted fast burn engine could not be reached.The effects of burn time on cyclic variation, ignition delay time, rate of pressure rise and emissions were also examined. Decreasing burn time resulted in increased rates of pressure rise and hydrocarbon emissions and reduced cyclic variation and ignition delay time. Reduction in NOx emissions was noted when burn time was decreased while operating with exhaust gas recirculation.