This illustration shows the parameters of a cam's lobe separation angle as defined by the intake and exhaust centerlines. As you can see, changing this angle changes the amount of overlap the cam has, or the amount of time both the intake and exhaust valves in a given cylinder are open at the same time. The diagram also shows the four valve timing points: intake opening (IO), intake closing (IC), exhaust opening (EO) and exhaust closing (EC). As you can see, changing the cam's lobe separation angle also changes these timing points-and therefore the engine's power production characteristics. Illustration courtesy of Comp Cams.