A cam shaft controls the timing of the opening and closing of the the engine valves.
On a modern combustion engine, the camshaft is what allows the valves to open and close during the combustion process. During the combustion process, the timing of the opening and closing of the valves directly affects the power output of the vehicle. Installation of a performance camshaft with performance cams can increase the horsepower of the engine.
Valve lift refers specifically to the distance the valve is lifted of the valve seat. The distance is measured in inches. Two valves are controlled by the camshaft: the intake valve and the exhaust valve. The intake valves open to allow the air and fuel mixture into the cylinders. The exhaust valve allows the combusted gasses to be expelled from the engine. Opening the valves more quickly and for a longer duration typically will yield more power in the engine. The S&S 563 camshaft has a valve lift of 0.560 inches.
Duration is a measurement of the angles on the camshaft the valve remains lifted from a specific measure from the valve seat. The specific measure is in inches. For example, a measurement might be duration at .050, or 180 degrees. This duration measurement indicates the point at which the angle is measured is 0.05 inches from the point at which the valve is lifted 0.05 inches from the seat until the point it it returns to 0.05 inches from the seat. In this case, it is 180 degrees, or a half turn of the camshaft. The S&S camshaft duration is measured with the specification duration at 0.053, or 276 degrees.
Open and Close
The camshaft open and close measurements indicate the point at which the valve is opened and closed during the rotation of the camshaft. The measurement is expressed in angles, indicating the angle from center line the camshaft has rotated when the valve opens. The center line is the point at which the lobe of the camshaft is highest. The S&S camshaft open and close measurements for the intake are 32 degrees and 60 degrees, respectively. The S&S camshaft open and close measurements for the exhaust are 64 degrees and 32 degrees, respectively.