A secondary effect of increased duration can be increased "overlap", which determines the length of time that both the intake and exhaust valves are open. It is overlap which most affects idle quality, in as much as the "blow-through" of the intake charge immediately back out through the exhaust valve which occurs during overlap reduces engine efficiency, and is greatest during low RPM operation. In general, increasing a camshaft's duration typically increases the overlap, unless the Lobe Separation Angle is increased to compensate.