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Side by side, a roller cam’s lobes (left) seem much brawnier and beefier than those of a flat tappet. This shape is by no means an indication of the difference in delivered cam specifications, but rather is dictated by the geometry of the respective lifter’s contact with the lobe. The best way to compare cam specs is to look at the duration throughout the lift range. Generally, a roller can achieve a higher velocity than a flat tappet, for more duration and quicker valve opening at high lift.