Flat-4: Meaning (information, definition, explanation, facts)

A Flat-4 is a four cylinder internal combustion engine where the cylinders are arranged in a flat configuration. This is not a common configuration, but some brands of automobile have favored such engines and it is a common configuration for smaller aircraft engines.

Volkswagen used the flat-4 extensively in their early days, in the VW Beetle and most early VW designs. Porsche also used almost the same engine in the Porsche 356 and Porsche 912 among others.

Subaru also produces water-cooled flat-4 engines that are confusingly marketed as H-4, by which they mean Horizontal rather than the H cross-section normally meant by H engine.