Learned something, thought I'd share.
Camshaft duration is a measurement of how long the valve stays open in crankshaft degrees. And the measurement is taken from one specific lift point to that same closing point on the closing end of the ramp.
But, since duration is measured at the cam itself from the manufacturer you would think that rocker ratio is totally independent of this. Well yes, and no, and yes again.
What really matters is the lift at the valve (obviously) and if we measure the lift at the valve at a specific point (say .05 again) with a higher ratio rocker, the valve will reach that point slightly sooner and slightly later, creating a slightly longer degree arc.
Although, if we were to measure valve lift at .00000000000000000000001 (you get the point) there would be no difference in duration, as the cam begins to lift the valve when it begins to lift the valve, period. Rocker ratio cannot change this. However, we do not end the measurement at the very closing point of the ramp. Why not? Probably because there is a negligible amount of air flow at .00000000000000000000001 lift.
Is your head spinning? Mine is.
So in conclusion, yes rocker ratio can affect dynamic duration. The rule of thumb seems to be 2 degrees for every .1 ratio on the rocker arm.
In otherwords, if you had 220 degrees of duration with a 1.6 rocker on an LS1, you'd have 222 degrees with a 1.7 rocker. My cam is a 236 in, 242 ex. split duration with a 1.5 rocker and with my new 1.65 rockers, my duration will jump to 239 in. and 245 ex.
