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 in 1950 with the Lancia Aurelia, other manufacturers took note and soon other V6 engines were in use. The design really took off after the 1962 introduction of the Buick Special. Though the model was not a spectacular success, it was the first mass-produced V6 engine.
A V6 is not a perfectly balanced engine and benefits from some counterbalancing and harmonic damping. The optimal angle to minimize vibrations in the V6 is 60°, and this is commonly used. The most common 60° V6s were built by Ford European subsidiaries : Essex V6, Cologne V6 and the more recent Duratec V6. The Alfa-Romeo V6 is also common.
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). This option was first used by Maserati, a long time V8 manufacturer, with the Citroën SM V6 engine. Many American V6 engines are 90° for this reason, as is the PRV (Peugeot-Renault-Volvo) V6, based on a canceled V8 design.
Narrow 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 (15°).
Other notable V6 bank angles:
- The 54° GM/Opel V6, designed to be narrower than normal for use in small front wheel drive cars.
- The 65° Ferrari Dino V6
Odd and even firing
Many V6 engines have been based on V8 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 a 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:
- 0° : Fire cylinder 1
- 30° :
- 60° :
- 90° : Fire cylinder 6
- 300°: Fire cylinder 5
- 390°: Fire cylinder 4
- 510°: Fire cylinder 3
- 600°: Fire cylinder 2
- 720°: Fire cylinder 1 (same as 0°)
In 1977, General Motors introduced a unique "split-pin crankshaft" in the GM 3800 engine. 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.
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 F2 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 1956-06-30 at the age of 24.
The Dino V6 underwent several evolutions, and—with an increased engine displacement—competed in the 2.5 L formula.
Until the advent of wing cars, a wide 120° bank angle was appealing for racing engine designers as it permits a low center of gravity. It was 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. A further evolution of the Ferrari Dino built for new Formula One 1.5 liter regulations engines had this configuration.
This 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 used them for the Lancia Stratos which would became the most successful car in Rally racing history.
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 2 titles. This engine was further developed in a tubocharged 2 liter 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 liter 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.
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.
|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, H|
|W||8, 9, 12, 16, 18|
|Other inline||H, VR, Opposed, U (Square), X|
|Other||Hemi, Radial, Rotary, Pistonless, Deltic, (Wankel)|
|Stroke cycles |
One • Two • Four • Six •
|Engine types |
Gas turbine • Piston • Jet • Rocket engine • Steam engine • Stirling engine • Tschudi• Twingle
Rotary • Wankel • Free-piston • Britalus • Coomber • Swing-piston • Orbital • Quasiturbine
Cylinder head porting • D slide • Four-stroke • Manifold • Multi • Piston • Poppet • Sleeve
|Piston layouts |
Single cylinder • Straight • Opposed • Flat • V • W • H • Deltic • Radial • Rocket engine nozzle • Rotary • Stelzer • Controlled Combustion • Bourke
|Motion mechanisms |
Cam • Connecting rod • Coomber rotary • Crank • Crank substitute • Crankshaft • Linkages (Evans • Peaucellier-Lipkin • Sector straight-line • Watt) • Double acting/differential cylinder