We could fill volumes spelling out the number of factors that affect an internal combustion engine's performance. Each component, each setting, each measurement and tolerance of every type combine to create a powerplant's performance characteristics. As we've said many times before, however, nothing defines the character of an engine more than its camshaft. Of all the measurements and specifications found in a camshaft, it's hard to underestimate the importance of the lobe separation angle, or LSA. Simply put, the LSA indicates the angle, in camshaft degrees, between the maximum lift points, or centerlines, on the intake lobe and the exhaust lobe. This figure, which is ground into the cam at the factory and cannot be changed, directly influences an engine's powerband. It's more complicated than that, of course, but the idea behind this project is straightforward. In short, we hit the dyno with our Coast High Performance 406 stroker test mule and tested three camshafts that carried identical specification-except for their lobe separation angles. How did it affect our engine's powerband? Read on to find out.
As we worked with Comp Cams engineer Billy Godbold to spec out this experiment and interpret the results, we were looking to discuss this complicated subject as simply as possible. For Godbold, this started with the term lobe separation angle. "It's doesn't mean anything except for how it affects the camshaft centerlines," he explained. "You determine the centerlines, which determines overlap, and that has performance effects." To be more specific, every cam lobe has a given number of degrees of duration, and there is a midpoint to this event. This midpoint is referred to as a centerline, and there is one for the intake and one for the exhaust. The intake centerline is used to position the cam in the engine. The exhaust lobe centerline doesn't come into play during installation or cam degreeing, but it is essential to calculating lobe separation angle. The LSA is calculated by adding the intake centerline and the exhaust centerline, then dividing by two. 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; 220 2 = 110). In fact, the cam we already had in this 406 was a standard Comp XR300HR with a 110-degree lobe separation. Our other two 'sticks were custom ground to have all the same specs as our 110-degree specimen, except that one had a 107-degree LSA and the other a 113-degree LSA.
Quick Notes
What We Did
Dyno-tested three camshafts with identical specs except for lobe separation angle.
Bottom Line
The effects are subtle, but lobe separation angle does affect an engine's powerband.
Price
Only the power you give up by choosing the wrong LSA.
To the naked eye, these could...
To the naked eye, these could be three identical camshafts, and in fact they almost are. Except for their lobe separation angles-and the valve timing events dictated by the LSA-these cams are indistinguishable from one another.
Just as you can't tell our...
Just as you can't tell our three test camshafts apart by sight, each one's lobe separation angle is just as impenetrable to the naked eye. The intake and exhaust centerlines of each pair of lobes, however, influence where in the powerband an engine makes power.
This illustration shows the...
This illustration shows the parameters of a cam's lobe separation angle as defined by the intake and exhaust centerlines. As you can see, changing this angle changes the amount of overlap the cam has, or the amount of time both the intake and exhaust valves in a given cylinder are open at the same time. The diagram also shows the four valve timing points: intake opening (IO), intake closing (IC), exhaust opening (EO) and exhaust closing (EC). As you can see, changing the cam's lobe separation angle also changes these timing points-and therefore the engine's power production characteristics. Illustration courtesy of Comp Cams.