Duel Over Head Camshaft,the reason an engine works a lot better is the engineers can design the intake duration and exhaust duration differently on separate cams than if they on one single camshaft,just by off setting the cam drive on each camshaft they can achieve more horse power.If you think this is technical try HCVVT.Hydraulically Controlled Variable Valve Timing.Does the same thing only a lot better and it's computer controlled.