A parameter determination system includes first and second difference modules, a ratio module, and an M index module. The first difference module determines a first crankshaft angle of a combustion event of an engine, determines a second crankshaft angle of the combustion event of the engine, and determines a first difference between the first and second crankshaft angles. The second difference module determines a third crankshaft angle of the combustion event of the engine, determines a fourth crankshaft angle of the combustion event of the engine, and determines a second difference between the third and fourth crankshaft angles. The ratio module determines a ratio of the first difference to the second difference. The M index module determines an M index value for the Wiebe function based on the ratio and displays the M index value on a display.