Red marquis at 10:55, 24 May 2010

2010-05-24T10:55:32Z

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

The flat-12 is wider (but significantly lower in height) than a [[V12 engine|V12]]. Despite the advantage of having a lower center of gravity than a V12, that advantage can be somewhat offset by the need for a higher mounting height in the engine bay to provide clearance for the exhaust system (six runners on either side). Whereas a V12 can be used in front-engined or mid-engined applications, a flat-12 is used exclusively in mid-engined sports cars. In addition, because it has no advantage in terms of vibrations compared to the more commonly-used V-12, the design is rarely used on production cars.

Flat-12 engines are generally not true horizontally opposed engines ([[flat engine|boxer]]), but rather 180° [[V engine|V]]-engines. A true boxer has one crank pin per piston, while in the 180° V-engine, two opposing pistons share the same crank pin.

The flat design was used in [[Formula One]] and [[Endurance racing]]. However, when [[Ground effect in cars|wing-cars]] requiring air-flow venturis 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 512 F1]], but a more classical V12 was chosen for the new 3 litre F1.

The [[Porsche 917]] endurance racing car (introduced in 1969, for the Sport category) was powered by an air-cooled flat-12. This engine was an evolution of the Porsche [[flat-8]] boxer engine and used identical cylinders to those found on the [[Porsche 908|908]], but differed in that it used a V12 type crankshaft.

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

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

A 4.4-5.0 L 180° flat-12 was later introduced by [[Ferrari]] in some of their production models, including the [[Ferrari Berlinetta Boxer|Berlinetta Boxer]] and [[Ferrari Testarossa|Testarossa]].

[[Motori Moderni]] designed a 3.5 litre flat-12 engine for [[Subaru]], which would be used in the 1990 [[Enzo Coloni Racing Car Systems|Coloni]] Formula One car. The Coloni−Subaru was not competitive and did not start a Grand Prix. The Motor Moderni flat-12 engine also appeared in detuned form in the [[Jiotto Caspita]] [[supercar]]. This only appeared in a single prototype and was not put into production.

In the early 1990s, [[Mercedes-Benz]] built their 3.5 litre [[M-291]] flat-12 engine for endurance racing. This engine employed a clever cylinder-head design in which the exhaust ports are located where the intake ports would normally be (on top of the engine, pointing upwards). The intake ports are then re-located between the intake and exhaust camshafts, just above the spark-plugs, pointing at an outward angle from the vertical. By locating the entire exhaust system on top, rather than underneath the engine, a much lower mounting height was achieved for this engine in the engine-bay of their racing car, the [[Mercedes-Benz C291|C-291]] (and later [[Mercedes-Benz C292|C-292]]). Unfortunately, the engine suffered from oil scavenging problems early on in its development, and although the problem was eventually solved, changes in the rules by [[Fédération Internationale de l'Automobile|FIA]] and [[Automobile Club de l'Ouest|ACO]], effectively doomed the future prospects of what could otherwise have been a competitive engine.

[[Henry Meadows]] built a flat-12 petrol engine in World War II for the British Covenanter tank. In 1954, [[Panhard]] fitted a flat-12 (based on its earlier aircooled two-cylinder) in the [[Panhard EBR|EBR]] [[armored car]].<ref>Ogorkiewicz, R. M. ''AFV Weapons Profile 039 Panhard Armoured Cars'' (Windsor, Berks: Profile Publications).</ref>

==See Also==

{{Piston engine configurations}}

[[Category:Boxer engines]]

Flat-12 engine - Revision history

Red marquis at 10:55, 24 May 2010