Any chance you might do a video for a TURBO engine? I'm told the amount of overlap changes, and/or the timing of the opening/closing of the intake/exhaust valves, to help keep the compressed inlet charge at a higher pressure.
This is a great overall explanation, and the only concrete way to find maximum efficiency (per all the variables) of a particular engine is to experiment with different timing events. Swirl, quench, air velocity, turbulence etc etc etc affect every engine differently. We can install a cam with a general spec that is in the range of maximum efficiency, but the only way to be ideal is to adjust timing events. Fuel and timing often also require adjustment going from a Dyno to in the vehicle.
Negatively, it costs energy to overcome back pressure A complete vacuum is the impossible ideal. the closer you get to zero the better. Scavenging is taking back some of the work lost to back pressure
