Why must a two-stroke cycle engine always have an intake pressure boost?

Most 2-strokes don't either because they use the compression stroke to draw intake charge into the crank case. The intake charge lubes the bearings, then when the piston drops again on the power stroke it becomes pressurized. As the intake and exhaust ports become uncovered, the pressurized crankcase intake charge is pushed into the cylinder by the falling piston.

tiroshen