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A '''flat-12''' is an [[internal combustion engine]] in [[Flat engine|flat]] configuration, having 12 [[cylinder]]s.

The flat-12 is larger than a [[V12]] and has no advantage in terms of vibrations. Thus the design is rarely used on production cars.

Most of the flat-12 engines are not true horizontally opposed engines (boxer) but rather 180° [[V engine|V]] engines.  The real boxer has one crank pin per piston while in the 180° V engine two pistons share the same crank pin. With twelve cylinders both layouts are perfectly balanced.

It was used in [[Formula One]] and [[Endurance racing]], the flat engine concept had the advantage of a low [[center of gravity]]. When [[wing-cars]] requiring air-flow venturies came along in the late 1970s, the wide flat-layout obstructed the airflow and became obsolete.

In 1964-65, at the end of the 1.5 litre F1 era, [[Ferrari]] introduced a flat-12 on the Ferrari 1512, but a more classical V12 was chosen for the new 3 litre F1. 

The [[Porsche 917]] endurance racing car (introduced in 1968, for the Sport category) was powered by an air-cooled flat-12. This engine was an opposed piston design, a direct evolution of the Porsche [[flat-8]] engine.

The domination of the Porsche 917 over the [[V12]]-powered [[Ferrari 512]] probably influenced Ferrari, for they returned to the flat-12 in 3 litre water-cooled form for its prototypes and Formula One cars.

The Ferrari flat-12 design was successful and influential especially on Italian manufacturers, [[Alfa-Romeo]] was also successful in [[endurance]] with a flat-12 while the [[Tecno]] Formula One flat-12 was a failure.

A 4.4-5.0 L 180° V12 was later introduced by [[Ferrari]] in some of its production models, including the [[Ferrari Berlinetta Boxer|Berlinetta Boxer]] and [[Ferrari Testarossa|Testarossa]].

[[Category:Piston engine configurations]]