It’s easy to see how roller cams improve performance. These two contain similar .050-inch duration and valve lift specifications, but the roller lobe (right) reaches peak valve lift much quicker and maintains it longer than the high-performance flat-tappet (left). A roller cam holds the valve open longer at higher lifts, allowing the engine to ingest more air to improve performance, but it also increases the amount of time the valve remains fully seated, which improves idle and drivability.