Overall overlap, or lobe center understanding?? ¿.

Sure. Lets say we gotta 440 with a single plane intake. Not that it matters, but lets say we got 9.5 compression. We gotta cam in it now with say 60* overlap. Overlap, when both intake and exhaust valves are open at the same time. We take that out and replace it with a cam that has 108* overlap. Why did our power go to hell? Because both valves are being held open for a longer period of time. This makes the engine think it has a hole in the intake. A vacuum leak if you will. The cylinder adjacent to the overlap cylinder has the intake valve open while the two valves are still open on the other cylinder. As the piston moves down in the cylinder with the intake valve open, it pulls in exhaust from the adjacent cylinder where those valves are hangin open, INSTEAD of through the intake and carburetor. Since the piston in our "overlap" cylinder is on the way UP, and the piston in the adjacent cylinder is on the way DOWN, the pressure drop is greater there than through the carburetor and intake, so the adjacent cylinder pulls in the exhaust from the overlap cylinder. Not good for power. I gave the example with a single plane because it's easier to see. It can happen with a dual plane as well, just not as prevalent. This is why large amounts of overlap and a single plane intake on the street usually don't work out too well.