A two-stroke internal combustion engine (30) is disclosed. Fuel efficiency is improved and extended over a wide power band by an inlet air valve (108) which controls the air charge and maintains a constant compression ratio. An integrated positive displacement supercharger (50) provides adequate air charge at all power levels and recovers compressor power from unused supercharged air. An integrated post combustion chamber (48) extends the power stroke by mixing combustion gases with ambient air for farther expansion and power production. Exhaust noise is reduced because the combustion gases are vented from the engine at lower pressure, lower velocity and temperature. The opposed cylinder design provides nearly continuous power by combining supercharger power recovery with extended power strokes.