Thread: Rocker ratio/duration

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rocker arms if longer or shorter only effect lift . with a longer rocker arm moving it up or down can make the engine think you moved the cam duration two to four degrees .the only thing that can add to making the duration bigger is the lifter size from 842.875.903 to 937 jesel bigger 1.060 as the bore gets bigger then the bigger the face of lifter gets . with some size roller lifters the roller wheel may be bigger that would be very small amount . any time i build a custom cam the master numbers are raw the dur is made in to the cam and only can be moved a very small amount with size of lifter . rocker arms only will move lift . cam lash can make the lift and dur move a small amount .engine will see it as a bigger cam with less lash or small cam with more lash but should not move it to much .003 up or down if you take to much lash out you can take valve seat time out. then the valves never have time for heat to get out of them and end up with burnt or cupped valves