V6 engine

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A V6 engine is a V engine with six cylinders. It is the second most common engine configuration in modern cars after the inline four; it shares with that engine a compactness well suited to the popular front-wheel drive layout, and is becoming more common as car weights increase.

The first V6 was introduced by Lancia in 1950 with the Lancia Aurelia. Other manufacturers took note and soon other V6 engines were in use. In 1959, GMC introduced a heavy duty 305 cubic inch (5 liter 60-degree V6 for use in their pickup trucks and Suburbans, an engine design that was later enlarged to 478 cubic inches (7.8 liters) for heavy truck and bus use.

The design really took off after the 1962 introduction of the Buick Special, which offered a 90 degree V6 with an uneven firing order that shared some parts commonality with a small Buick V8 of the period. Though the Buick Special was not a spectacular success, it was the first instance of a mass-produced V6 engine designed specifically for passenger automobiles. In 1983 Nissan produced Japan's first V6 engine with the VG series.

Modern V6 engines commonly range in displacement from 2.5 L to 4.0 L, though larger and smaller examples have been produced.

Contents 1 V angles 2 Odd and even firing 3 Racing use 4 Notes 5 External links

[edit] V angles

The ideal cylinder bank angle for a V6 is 60 degrees, which design tends to minimize vibration and encourage cancellation of reciprocating forces. The most common 60 degree V6s were built by General Motors (the heavy duty commercial models, as well as a design used in many GM front wheel drive cars), Ford European subsidiaries : Essex V6, Cologne V6 and the more recent Duratec V6. The Alfa-Romeo V6 is also common, and has been voted as the best engine of the year in 2000.

90 degree V6 engines have also been produced, often to take advantage of production-line tooling set up to produce V8 engines (for which a 90 degree arrangement is optimal). This design was first used by Buick when it introduced its 198 in³ Fireball V6 as the standard engine in the 1962 Special. Other examples include the Maserati V6 used in the Citroën SM, the PRV V6, Chevrolet's 4.3 L Vortec 4300 and Chrysler's 3.9 L Magnum V6 and 3.7 L PowerTech V6. The Buick V6 was notable because it introduced the concept of uneven firing, which was a natural result of the 90 degree layout. These engines were often referred to by mechanics as "shakers," due to the tendency of the engine to bounce around at idle speed.

Narrower angle V6 engines are very compact but suffer from severe vibration problems. More recently, Volkswagen have used such a design, known as the VR6 engine. In this engine, both banks share the same cylinder head and are extremely close together. Electro-Motive produced a 6 cylinder version of their model 567 Diesel locomotive engine, which has a 45 degree cylinder angle.

Other notable V6 bank angles:

• The 10.6° and 15° Volkswagen VR6, a V6 with such a narrow angle it shares all its characteristics with the straight-6, such as its firing order and use of a single cylinder head. It is not a true V, but rather a staggered-bank in-line six.
• The 54° GM/Opel V6, designed to be narrower than normal for use in small front-wheel drive cars.
• The 65° Ferrari Dino V6. The engine was originally fed by carburetors. A 60° angle was limiting the size of the carburetors, while a 65° angle allowed to mount larger carburetors to the expense of a slight increase of vibrations.
• The 120° V220/V300T V6 engines built by Bombardier for use in light aircraft. This layout allows for a shorter crankshaft and a more compact engine. It also allows for the use of a firing order that is in harmony with the layout, unlike the opposed (180 degree) 6 cylinder engines it is meant to replace.

Due to the odd number of cylinders in each bank, all V6 designs are inherently out of balance and thus benefit from some auxiliary counterbalancing. Also, the V6 can develop significant odd-order harmonic crankshaft vibration, an effect often counteracted by the use of a heavy duty harmonic damper to avoid possible crankshaft failure at higher engine speeds.

[edit] Odd and even firing

Many V6 engines have been based on V8 engine designs. One characteristic of these engines is a notorious odd-firing behavior.

Purpose-built V6 engines use one crankpin per cylinder for a smooth ignition 120° ignition pattern. In contrast, most V8 engines share a common crankpin between opposite cylinders in each bank. That is, the crankshaft has just four pins for eight cylinders, and a cylinder fires every 90° for smooth operation.

V6 engines that are converted from V8 engines often have three shared crankpins arranged at 120° from each other, similar to an inline 3-cylinder with two pistons per crankpin. If the cylinder banks are arranged at 90° (as they commonly are in V8-derived V6s), this leads to a firing pattern with groups of two cylinders separated by 90° of rotation, and groups separated by 150° of rotation.

An example is the Buick 231 odd-fire, which has a firing order 1-6-5-4-3-2. As the crankshaft is rotated through the 720° required for all cylinders to fire, the following events occur on 30° boundaries:

Nissan uses the firing order 1-2-3-4-5-6 in some of the V6 engines they make.

In 1977, Buick introduced a unique "split-pin crankshaft" in the 231. 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 produce a crankshaft that is strong enough. In 1986 the similarly-designed 90° PRV engine adopted the same 30° crankshaft offset design to even out its firing.

[edit] Racing use

The V6 engine was introduced into racing by the Ferrari Dino V6. Alfredo Ferrari (nicknamed Dino), the only legitimate son of Enzo Ferrari, suggested to him the development of a 1.5 L DOHC V6 engine for Formula Two at the end of 1955. Soon afterwards, Alfredo fell ill, suffering from muscular dystrophy. While in hospital, he discussed technical details with the engineer Vittorio Jano. Dino would never see the engine; he died on 30 May 1956 at the age of 24.

The Dino V6 underwent several evolutions, including an increased engine displacement to 2417 cc, for use in the Ferrari 246 Formula One car in 1958.^[1][2]

The use of a wide 120° bank angle is appealing for racing engine designers as it permits a low center of gravity. This design is even considered superior to the flat-6 in that it leaves more space under the engine for exhaust pipes; thus the crankshaft can be placed lower in the car. The Ferrari 156 built for new Formula One 1.5 L regulations used a Dino V6 engine with this configuration.^[3]

The Dino V6 engine saw a new evolution in 1966 when it was adapted to road use and produced by a Ferrari-Fiat joint-venture for the Fiat Dino and Dino 206 GT (this car was made by Ferrari but sold under the brand Dino). This new version was redesigned by Aurelio Lampredi initially as a 65° 2.0 L V6 with an aluminum block but was replaced in 1969 by a 2.4 L cast-iron block version (the Dino car was renamed the 246GT).

The Fiat Dino and Dino 246GT were phased out in 1974, but 500 engines among the last built were delivered to Lancia, who was like Ferrari already under the control of Fiat. Lancia used them for the Lancia Stratos which would become one of the most successful rally cars of the decade.

The Alfa Romeo V6 was designed in the 1970's by Giuseppe Busso, the first car to use them being the Alfa Romeo 6. The over-square V6, with aluminium alloy block and heads, has seen continuous use in road vehicles, from the Alfetta GTV6 onwards. The 164 introduced a 3.0L V6, and in 1992, a 3.0L DOHC 24 valve version. The Alfa 156 introduced a 2.5 L DOHC 24 valve version in 1997. The engine capacity was later increased to 3.2L, where it found application in the 156 GTA, 147 GTA and the Alfa GT. Production was discontinued in 2005.

Another influential V6 design 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 Two titles. This engine was further developed in a tubocharged 2 L version that competed in Sports car and finally won the 24 Hours of Le Mans in 1978 with a Renault-Alpine A 442 chassis.

The capacity of this engine was reduced to 1.5 L to power the Formula One Renault RS01. Despite frequent breakdowns that resulted in the nickname of the 'Little Yellow Teapot', the 1.5 L finally saw good results in 1979.

Ferrari followed Renault in the turbo revolution by introducing a turbocharged derivative of the Dino design (a 1.5 L 120° V6) with the Ferrari 126.^[4] However, the 120° design was not considered optimum for the wing cars of the era and later engines used a wider V angle.

Both Renault and Ferrari failed in their attempt to win the Drivers's Championship with V6 Turbo engines. The first turbocharged engine to win the championship was the Straight-4 BMW.

They were followed by a new generation of Formula One engines, the most successful of these being the TAG V6 (designed by Porsche) and the Honda V6. This new generation of engines were characterized by odd V angles (around 80°). The choice of these angles was mainly driven by aerodynamic consideration. Despite their unbalanced designs these engines were both quickly reliable and competitive; this is generally viewed as a consequence of the quick progress of CAD techniques in that era.

[edit] Notes

[edit] External links

• Understanding the odd-fire V6

Piston engine configurations
Straight	Single, 2, 3, 4, 5, 6, 8, 9, 10, 12, 14
V	2, 4, 5, 6, 8, 10, 12, 16, 20, 24
Flat	2, 4, 6, 8, 10, 12, 16
W	8, 9, 12, 16, 18
Other inline	H, VR, Opposed, U (Square), X
Other	Radial, Rotary, Pistonless (Wankel)