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Seems that people say that changing to a higher rocker ratio increases cam duration with the lift, like 4 degrees from 1.5 to 1.6, I am not too sure I buy this, I can see where area under the curve will change but not duration, I'm I missing something



It's just a comparison thing. The cams duration will remain the same, but the duration and lift at the valve will change with rocker ratio. If the rocker ratio was 1:1 (and assuming zero lash) the valve duration and lift would be the same as the cam. The normal 1.5:1 rocker ratio is what most comparisons are based from. Changing to a higher ratio rocker arm, results in higher lifts at all points, so if you compare valve durations at the same lift, the higher ratio rocker arm will reach the same lifts sooner/later making the valves see "comparably" more duration at the valves.