[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] Lift and Duration
We all know that stepping up to a cam with a little more lift and duration can yield a nice gain in performance.
[/SIZE][/FONT][FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] Many people incorrectly assume that a change in rocker arm ratio has no effect on the duration the valves are open. In actuality there is some change to the duration at the valve depending on the lobe profile of the camshaft.
Comp Cams explains that by lifting the valve an additional 7-8%, but beginning and ending the lift at the same point, the opening and closing rates become steeper. This increases duration, measured at the valve at 0.050" lift, by 1-2 degrees. You can measure the actual duration change by using a degree wheel and dial indicator set on the valve retainer.
Coincidentally the principle of a steeper rate of opening and closing is what Comp Cams has engineered into their Extreme energy camshafts to enable more valve duration for a given lobe duration.[/SIZE][/FONT]