Hey guys I was just wondering which one of the two is more important for low end power/torque (lift or duration). I have always thought more lift was considered when building a low rpm engine where as longer duration is used for high rpm applications. Can anyone confirm this??
Less duration shifts the torque peak to a lower RPM. Lift can have varying effects, but its basically based on the heads. Heads will flow better at higher lifts up to a certain point. Above that lift they will start flowing less. Many stock heads improve their lift up to about .4 or .5 inches. Adding more lift by swapping to higher ratio rockers can shift the torque peak up a little in the RPMs because it has the effect of adding a tiny bit of duration. Duration measured at .050 lift translates to more lift faster at the valve itself. Its usually a tiny distinction. If you want your torque to peak at 2000 rpms and you switch to higher ratio rockers, it might now peak at 2075 or something.
So in a nutshell, use the duration and head flow to determine where the torque will peak, then to maximize the power curves, select a lift that takes advantage of what the head has to offer and no more. If your head starts dropping flow above .5" lift, then chose a combo that won't take you over .5" lift.
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