The windowed piston allows intake timing to be 360° of rotation. The reason the reed valve doesn't work without the window is because the reed valve is otherwise restrictive and there isn't enough blowback for it to function properly. However with 360° timing it can pull in more air and infact have positive crank case pressure, which is, in a way, supercharging
All 2 strokes are supercharged. The diesels via a crank drive blower, and motorcycle and utility engines typically uses the conrod and crank case as a pump.
There's just too much pressure in the cylinder for air to flow in at ambient pressure.
On the upstroke a vacuum is formed, and suddenly the normal air is 10+ psi higher by relation and forces in. On our engines the piston blocks the intake on the down stroke and the transfers are unblocked.
Now on the down stroke that ambient pressure is raised up as the conrod, and piston goes towards bdc.
Pressure equals force times area. Boyles lawThe mass of air is the same: we get higher pressure from the lower area. When properly functioning, we get the vacuum from the air ultimately exhausting rather than blowing back into the case. Now there's still absolute pressure because no seal is perfect but the vast majority is out the exhaust port.
You can convert a piston port two stroke engine into an air compressor with two check valves where the spark plugs goes, and blocking all ports.
A six to one compression of 60cc swept is 5 times the ambient pressure. Correct me if I'm wrong but I'm under the impression we just raise the pressure by the same factor we divide the area by, then subtract ambient pressure because we are calculating pressure above ambient, not absolute pressure. But that's not relevant.
