[JSeery]

Cam overlap is the time when both the intake valve and the exhaust valve are open around TDC. Split overlap is where both valve are at the same height above the valve seat and should be at TDC. I think the way Ron is using it is check TDC against both of the valves being in the same position.

As Kurt posted above: ...as the exhaust just is about closed the intake will just start opening, when you have both valves equally just a little open the piston should be at tdc for most cams