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A V6 is an internal combustion piston engine with six cylinders in a "V" configuration. It is the second most common engine configuration in modern cars after the straight-4; it shares with that engine a compactness very suited to the popular front wheel drive layout, and is becoming more popular as car weights increase.

The first V6 was introduced by Lancia on the 1924 Lancia Lambda, but it made little impact. The design was reintroduced by the company in 1950 with the Lancia Aurelia; this time, other manufacturers took note and soon other V6 engines were in use.

A V6 is not a perfectly balanced engine and benefits from some counterbalancing and harmonic damping. The optimal angle to minimise vibrations in the V6 is 60°, and this is commonly used. 90° V6 engines have also been produced, often to take advantage of production-line machinery set up for V8 engines (for which 90° is optimal). Many American V6 engines are 90° for this reason, as is the PRV (Peugeot-Renault-Volvo) V6, based on a cancelled V8 design.

A 90° V6 can have shared crankpins between two 'opposite' cylinders, but this results in uneven firing. Using a crankpin that is 'split' and offset by 30° of rotation results in smooth even firing. Such a 'split' crankpin is weaker than a straight one, but modern materials and manufacturing give a crankshaft that is quite strong enough.

Even narrower angle V6 engines are very compact but suffer from vibration. Lancia's 1924 engine was such a design; Lancia produced similar (but mostly V4) engines until the 1970s. More recently, Volkswagen have used such a design, known as the VR6. In this engine, both banks share the same cylinder head and are extremely close together.

Racing use

V6 engines were popular in racing. Early on, it was popular to use a 120° V angle, to make the engine fit as low as possible inside the car. Some Ferrari Dino V6 Formula One 1.5 litre engines had this configuration.

Another use of the V6 was the Renault-Gordini CH1 V6, designed by François Castaing and Jean-Pierre Boudy, and introduced in 1973 in the Alpine-Renault A440. The CH1 was a 90° cast iron block V6, similar to the mass produced PRV engine in those two respects but otherwise dissimilar. It has been suggested that marketing purposes made the Renault-Gordini V6 adopt those characteristics of the PRV in the hope of associating the two in the public's mind.

Despite such considerations, this engine won the European 2 L prototype championship in 1974 and several European Formula 2 titles.

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