The Volkswagen air-cooled engine is a flat-4 "boxer" engine with four horizontally-opposed cast-iron cylinders, cast-aluminium alloy cylinder heads and pistons, magnesium crankcase, and forged steel crankshaft and connecting rods. The engine is cooled by the controlled passage of air directly over the hot parts of the engine.
Variations of the Air-cooled VW engine were produced by Volkswagen plants worldwide from 1936 until 2006 for use in Volkswagen's own vehicles, including the "Beetle" (Type 1), Transporter or "Bus" (Type 2), the 1500 and 1600 (Type 3), and the 411 and 412 (Type 4). Volkswagen air-cooled engines were also widely used in industrial, aircraft, and home-built applications.
Originally, the VW air-cooled engine had a displacement of 1.1L (~1100cc) and was rated at a horsepower of 34bhp. This engine was used in Beetles and Transporters from 1945 to 1953. It was a reliable, if not under-powered engine that was gradually upgraded over the years to displacements of 1.2L (~1200cc), 1.3L (~1300cc), 1.5L (~1500cc), and ultimately 1.6L (~1600cc).
Upon its introduction in 1966, the 1600cc proved to be a near-perfect combination for the North American market in terms of fuel economy, reliability, and power. In 1971, the air-cooled 1600 was changed one last time to upgrade the long-standing single-port intake heads to a dual-port intake, increasing the horsepower to 50bhp.