Lobe Separation Angle (LSA)
What it is: The distance between the intake centerline and the exhaust centerline. The angle can be determined by adding the intake and exhaust centerline numbers together and dividing by two (since the cam spins at half the crankshaft's speed). For example, a cam with a 106-degree intake centerline and a 114-degree exhaust centerline has a lobe separation angle of 110 degrees (106 + 114 = 220 2 = 110).
Why it's important: LSA influences engine operation in multiple ways (we've included a chart elsewhere) but primarily determines where peak torque will occur and how broad the torque band will be.
Overlap
What it is: The amount of time, measured in crankshaft degrees, that both the intake valve and the exhaust valve are open. This situation happens at the end of the exhaust stroke and the beginning of the intake stroke. Increasing lift or duration or decreasing lobe separation angle increases overlap.
Why it's important: Some overlap is desirable, since the outgoing exhaust gases help pull in the fresh intake charge. Too much, however, leads to a contaminated charge that doesn't burn well. An increase in overlap generally improves top-end power at the expense of low-end grunt and reduces idle quality.
Single-pattern cam
What it is: A cam with identical intake and exhaust lobe profiles, employing equal amounts of duration and lift. For example, a Crane Energizer 266 H10 (PN 10004) has 266 degrees advertised duration, 210 degrees duration at 0.050 inch, and 0.440 inch lift on both the intake and exhaust sides.
Why it's important: Some engines, especially those with heads that flow well on the exhaust side, may work best with a single-pattern cam.
Valve Lift
What it is: Lobe lift multiplied by the rocker arm ratio. For example, if we have a lobe that measures 0.334 inch and are running a 1.5:1 rocker arm ratio, 0.334 x 1.5 = 0.501 inch valve lift. Running a 1.6:1 rocker arm creates 0.534 inch valve lift.
Why it's important: It's the distance the valve is lifted off its seat at the cam lobe's highest point and influences how much power an engine will make within its rpm range.