The experimental and analytical results from a study of a single cylinder di diesel with various combustion chamber arrangements are presented. The study investigates the properties of toroidal and cylindrical piston cavities with different fuel spray paths.It is shown that seemingly similar combustion arrangements behave differently. One system (optimized cylindrical) demonstrates an improved thermal efficiency and reduced sensitivity to changes in injection timing.Heat release data computed from p-θ diagram over a wide range of power, speed, and injection timing is presented. From this data, a method of calculating heat release curves for cycle synthesis is identified. The method is based on the summation of two “Wiebe” type curves. Results show good correlation between experimental and calculated cycle parameters for the systems tested.