Cam Centerline & Lobe Separation Angle

When you need it

When degreeing a cam in, verifying that a cam card matches what is actually in the box, or working out what an unmarked used cam really is.

Four numbers encode everything

Duration, both centerlines, the lobe separation angle, overlap and the ground-in advance all fall out of the four opening and closing points. If you have degreed the cam, you have everything you need to describe it.

It also works the other way: if your measured figures disagree with the card, you have either a mis-ground cam, a stretched chain, an off-index gear or a measurement error — and it is worth finding out which before the heads go on.

Advance, and why cams come with it

Most cams are ground with around four degrees of advance built in, which puts the intake centerline ahead of the lobe separation angle. Advancing a cam strengthens the bottom end and moves the whole power band down; retarding it does the opposite.

Installed advance is what you actually have after degreeing, which is not necessarily what the card claims. Timing sets vary, keyways vary, and chains stretch.

Do not mix duration standards

Advertised duration is measured at a small tappet lift, usually 0.006 inch. The 0.050 inch figure is the industry comparison standard and will always be smaller — often by thirty or forty degrees. Feed this calculator seat-to-seat figures.