turtle22, doordie used to have a gif showing how the exhaust pipe creates the reversion pulses, I tried to find it, but I could not. doordie may be able to repost it, as I really loved to see it.
The concept is not about back pressure, as much as it is about exhaust volume or internal size of the exhaust, starting at the piston and ending at the exhaust pipe rear cone. The KPIS varies that size ( volume).
It is like having an exhaust pipe for low RPM power, then switching to an exhaust pipe for high RPM power, only it is done automatically by using centrifugal weights that expand with RPM and move a lever that enlarge the exhasut port volume (size/shape).
I really hope doordie can repost that gif of the reversion pulses.
The shape of the pipe cones dictate the reversion pulses and that creates the scavenging effect to draw in the next charge.
I will try to PM doordie to repost that gif.
John