The pressure-charger shown in the diagrams is a turbocharger, not a positive-displacement supercharger. The engine (whether four-stroke or two-stroke) has a conventional valve or port layout, but an additional "compression control valve" (CCV) is in the cylinder head. The servo mechanism, operated by inlet manifold pressure, controls the lift of the CCV during part of the compression stroke and releases air from the cylinder to the exhaust manifold.