A method of measuring exhaust velocity with respect to crank angle in a 4-stroke spark ignition engine is described as is a new method of automatically selecting a crank angle in an engine under running conditions. The method of obtaining the exhaust velocity, using the selected crank angle, is also dealt with. The exhaust velocity measured for both motoring and firing conditions is included. The results provided for the firing conditions include different exhaust configurations. The cycle-to-cycle fluctuation is also provided for the above configurations.