Panic, very interesting about the “triangle”. Makes a lot of sense to me that to a point at least, the overlap amount would would be a big factor in how much vacuum that the exhaust wave could pull on the intake port.
In a more conventional head where the intake and exhaust valves sit side-by-side the scavenging effect may well pull on the intake port during overlap. But we are talking about the last of the stovebolt designs here:
scavenging must first evacuate the un-swept combustion chamber volume before it can start to work on the intake valve which sits shrouded in a recess in the head and completely covered by the piston at TDC. IMHO Just evacuating the un-swept combustion chamber is benefit enough from scavenging. Moreover, I think the shrouding of the intake deters reversion until very low RPM allowing for more degrees of overlap (a bigger triangle).
