V6

Design

Due to their short length, V6 engines are often used as the larger engine option for vehicles which are otherwise produced with inline-four engines, especially in transverse engine vehicles. A downside for luxury cars is that V6 engines produce more vibrations than straight-six engines. Some sports cars like the Porsche 911 use flat-six engines instead of V6 engines, due to their near perfect primary engine balance and lower centre of gravity (which improves the handling).

The displacement of modern V6 engines is typically between 2.5 and 4.0 L (153 and 244 cu in), though larger and smaller examples have been produced, such as the 1.8 L (110 cu in) Mazda V6 used in the 1991–1998 Mazda MX-3, or the 1.6 L (98 cu in) Mitsubishi V6 engine used in the 1992–1998 Mirage/Lancer, while the largest gasoline V6 built was the 7.8 L (478 cu in) GMC V6 used in the 1962 GMC C/K series 6500.

Balance and smoothness

All V6 engines with even firing spacing—regardless of the V-angle between the cylinder banks—are subject to a primary imbalance caused by each bank consisting of a straight-three engine, due to the odd number of cylinders in each bank. Straight-six engines and flat-six engines do not experience this imbalance. To reduce the vibrations caused by this imbalance, most V6 engines use a harmonic damper on the crankshaft and/or a counter-rotating balance shaft.

Six-cylinder designs have less pulsation in the power delivery than four-cylinder engines, due to the overlap in the power strokes of the six-cylinder engine. In a four-cylinder, four-stroke engine, only one piston is on a power stroke at any given time. Each piston comes to a complete stop and reverses direction before the next one starts its power stroke, which results in a gap between power strokes, especially at lower engine speeds (RPM). In a six-cylinder engine with an even firing interval, the next piston starts its power stroke 60° before the previous one finishes, which results in smoother delivery of power to the flywheel.

Comparing engines on a dynamometer, a V6 engine shows instantaneous torque peaks of 154% above mean torque and valleys of 139% below mean torque, with a small amount of negative torque (engine torque reversals) between power strokes. In the case of a four-cylinder engine, the peaks are approximately 270% above mean torque and 210% below mean torque, with 100% negative torque being delivered between strokes. However, a V6 with uneven firing intervals of 90° and 150° shows large torque variations of 185% above and 172% below mean torque.

Cylinder bank angles

Since 1991, Volkswagen has produced narrow angle VR6 engines with V-angles of 10.5 and 15 degrees shared by both banks of cylinders, in a design similar to the 1922–1976 Lancia V4 engine. These engines use a single cylinder head so are technically a straight engine with the name "VR6" coming from the combination of German words "Verkürzt" and "Reihenmotor" meaning "shortened inline engine". The VR6 engines were used in transverse engine front-wheel drive cars which were originally designed for inline-four engines. Due to the minimal extra length and width of the VR6 engine, it could be fitted to the engine compartments relatively easily, in order to provide a displacement increase of 60 percent .

Since there is no room in the V between the cylinder banks for an intake system, all the intakes are on one side of the engine, and all the exhausts are on the other side. It uses a firing order of 1-5-3-6-2-4 (which is the firing order used by most straight-six engines), rather than the common V6 firing order of 1-2-3-4-5-6 or 1-6-5-4-3-2.

A V-angle of 60 degrees is the optimal configuration for V6 engines regarding engine balance. When individual crank pins are used for each cylinder (i.e. using a six-throw crankshaft), an even firing interval of 120 degrees can be used. This firing interval is a multiple of the 60-degree V-angle; therefore, the combustion forces can be balanced through the use of the appropriate firing order.

The inline-three engine that forms each cylinder bank, however, produces unbalanced rotating and reciprocal forces. These forces remain unbalanced in all V6 engines, often leading to the use of a balance shaft to reduce the vibration.

The 1950 Lancia V6 engine was pioneering in its use of a six-throw crankshaft to reduce vibration. More recent designs often use a three-throw crankshaft with 'flying arms' between the crankpins allowing for an even firing interval of 120 degrees to be achieved. A pair of counterweights on the crankshaft can then be used to almost perfectly cancel out the primary forces and reduce the secondary vibrations to acceptable levels. The engine mounts can be designed to absorb these remaining vibrations.

A 60-degree V-angle results in a narrower engine overall than V6 engines with larger V-angles. This angle often results in the overall more compact engine, making the engine easier to fit either longitudinally or transversely in the engine compartment.

Use in automobiles

In 1906, a few years after 4 cylinder engines and V8 engines had come into existence, the first known V6 engine was built. This V6 engine was a single prototype automotive engine built by Marmon Motor Car Company in the United States. The engine did not reach production. Similarly, a single prototype engine was produced by Buick in 1918.

In 1910 Delahaye produced the first 30° 3.2-litre V6 which was installed in the 1911 Delahaye Type 44 automobile.

The Lancia V6 engine was introduced in the 1950 Lancia Aurelia. Lancia had been producing V4 engines for approximately 30 years, and one of the key goals was to reduce the vibrations compared with the V4 engine. The V6 engine used a 60 degree V-angle and six crankpins, resulting in an evenly-spaced firing order to reduce vibrations.

Other manufacturers took note and soon other V6 engines were designed. In 1959, the GMC V6 engine was introduced in the form of a 60-degree 305 cu in (5 L) petrol engine used in pickup trucks and carryalls. The Buick V6 engine was introduced in 1962 and was based on the all-alloy Buick 215 V8, which shared its 90° bank angle, but unlike the Buick V8, used all-cast iron construction. Initially an uneven-firing engine, Buick later redesigned the crankshaft to a "split-pin" configuration to create an "even-firing" version. After it became the 3800 V6 in 1988, the engine gained a reputation as a reliable, powerful, fuel-efficient workhorse that became a mainstay of GM's FWD mid-size and full-size cars. It was discontinued in 2008. Over 25 million units had been built, making it one of the most-produced engines in history, and it was on Ward's 10 Best Engines of the 20th century list.

Ford introduced its European road car engines in 1965 with the German division's Cologne V6, and the Ford Essex V6 engine, introduced by Ford's United Kingdom division in 1966; both engines used a 60-degree V-angle. The 1967 Dino 206 GT was Ferrari's first V6 road car, which had a 65-degree V-angle.

The 1979-2005 Alfa Romeo V6 engine was introduced in the Alfa Romeo Alfa 6 luxury sedan and later used in many other Alfa Romeo models. This engine used a 60 degree V-angle, an all-aluminium construction and two valves per cylinder. A turbocharged version was introduced in 1991 and a four valve per cylinder version was introduced in 1997. Also in 1970, the Citroën SM grand tourer was introduced, powered by a 90-degree V6 built by Maserati.

Motor racing

The Lancia Aurelia (the first series production car with a V6 engine) was also successful in motor racing. Four of the Aurelia B20 Coupes were entered in the 1951 Mille Miglia with the best placed cars finishing second and fourth. A tuned 3,102 cc (189 cu in) version of the Lancia V6 engine producing was 169 kW (230 PS) used in the Lancia D24. The D24 competed in sports car racing and won the 1953 Carrera Panamericana with Juan Manuel Fangio at the wheel.

The initial version of the Ferrari Dino engine was a 1.5 L (92 cu in) racing engine used in Formula Two racing in the 1957 season. It had a V-angle of 65 degrees and dual overhead camshafts. The Dino V6 underwent several evolutions, including a 2.4 L (146 cu in) version used in the 1958 Ferrari 246 Formula One racing car. A few years later, the 1961–1964 Ferrari 156 Formula One car used a new V6 engine with a V-angle of 120 degrees and a displacement of 1.5 L (92 cu in). This engine was shorter and lighter than the Ferrari Dino engine, and the simplicity and low center of gravity of the engine was an advantage in racing. It won a large number of races between 1961 and 1964. However, Ferrari's founder had a personal dislike of the 120 degree layout, preferring a 65 degree layout, and after that time it was replaced by other engines. The Dino engine was also used in the Lancia Stratos, which was a highly successful rally car that won the World Rally Championship in 1974, 1975 and 1976.

A notable racing use of the Alfa Romeo V6 engine was the Alfa Romeo 155 V6 TI, designed for the 1993 DTM season and equipped with a 2.5 L (150 cu in) engine making a peak power of 360 kW (490 PS) at 11,900 rpm.

The Renault-Gordini CH1 was a 90 degree V6 engine with an iron block. It was introduced in the 1973 Alpine-Renault A440 sports car racing car. This engine won the European 2 L prototype championship in 1974 and several European Formula Two Championships. A turbocharged 2.0 L (122 cu in) version was used in the Renault Alpine A442, which won the 24 Hours of Le Mans in 1978.

A turbocharged 1.5 L (92 cu in) version of the Renault-Gordini CH1 engine was introduced in the 1977 Renault RS01 Formula One car. Renault struggled with reliability issues in 1977 and 1978; however, the 1979 season saw some good results at a few races. In 1981, the Ferrari 126C Formula One car used a turbocharged V6 engine. Ferrari won the Formula One constructors' championship with turbocharged V6 engines in 1982 and 1983. Initial versions used a 120 degree V-angle, before switching to a 90 degree V-angle for the 1987 Ferrari F1/87 racing car. Other successful turbocharged V6 Formula One cars in the era of 1982–1988 were the McLaren MP4/2, McLaren MP4/3, McLaren MP4/4, Williams FW10, Williams FW11, Williams FW12, Lotus 95T, Lotus 97T, Lotus 98T, Lotus 99T and Lotus 100T.

Use in marine vessels and railway engines

V6 engines are popular powerplants in medium to large outboard motors.

The first V6 engine to reach production was built from 1908 to 1913 by the Deutz Gasmotoren Fabrik in Germany. These V6 engines were used as the generator for gasoline-electric railway engines.

Use in motorcycles

The Laverda V6 was a racing motorcycle which was unveiled at the 1977 Milan show. It entered the 1978 Bol d'Or 24 hour endurance race, however it retired with mechanical issues after approximately 8 hours.

Horex has produced road motorcycles with VR6 engines since 2012.