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Title: Rocker Arm Ratio
Describing the Principle: On most engines, it is important to open the valves more than the actual lift of the cam lobe. This can be done by changing the distances on the rocker arm from the pivot point to both ends of the rocker arm. The distance from the ends of the rocker arm to the pivot point are not the same. As shown in the drawing on the left, from the pushrod to the pivot point, the distance is 7/8 inches. From the valve to the pivot point there is a distance of 1 and 3/4 inches. This is similar to a first class lever being used to increase the length from the input to the output. In this case the length of the valve opening will be greater than the cam lobe lift. On this illustration, the valve opening will be approximately 2 times greater than the cam lobe lift. So the rocker arm ratio is stated as 1:2. With a cam lobe lift of 7/8 inches, the valve will open
1 and 3/4 inches. The exact rocker arm ratio will vary depending upon the engine manufacturer and the engine design, but the principle of rocker arm ratio, remains the same.
Back to Mechanical Principles
Describing the Principle: On most engines, it is important to open the valves more than the actual lift of the cam lobe. This can be done by changing the distances on the rocker arm from the pivot point to both ends of the rocker arm. The distance from the ends of the rocker arm to the pivot point are not the same. As shown in the drawing on the left, from the pushrod to the pivot point, the distance is 7/8 inches. From the valve to the pivot point there is a distance of 1 and 3/4 inches. This is similar to a first class lever being used to increase the length from the input to the output. In this case the length of the valve opening will be greater than the cam lobe lift. On this illustration, the valve opening will be approximately 2 times greater than the cam lobe lift. So the rocker arm ratio is stated as 1:2. With a cam lobe lift of 7/8 inches, the valve will open
1 and 3/4 inches. The exact rocker arm ratio will vary depending upon the engine manufacturer and the engine design, but the principle of rocker arm ratio, remains the same.
Back to Mechanical Principles
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