Line hot cam
Longer duration (higher number) improves top-end power but almost always sacrifices low-end torque.
Lower duration improves low-end torque and makes the car idle better, but it limits top-end power, and you can get only so much valve lift with a short duration cam due to the rate-of-lift limitations of the lifter.
DURATION: Duration is how long the cam holds the valves open.
Dyno tests show a broad torque curve and substantial power gains over the typical flat tappet SBC cams.Roller cams, which we’ll discuss below, have the advantage of allowing high rates of lift with relatively short duration.The confusing thing about duration is the difference between “advertised” and “at .050-lift” duration.It’s good to know exactly how each of these specs affects the engine’s performance, but one of the most important is duration, so pay special attention to that one.Also, look at the recommendations given by the cam companies for our six sample vehicles at the end of this article.