V6 engine

All V6 engines— regardless of the V-angle between the cylinder banks— are subject to a primary imbalance caused by each bank consisting of an inline-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, some V6 engines use counterweights 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 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 and annoying harshness, 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 150% above mean torque and valleys of 125% 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 nearly 300% above mean torque and valleys of 200% below mean torque, with 100% negative torque being delivered between strokes. However, a V6 with an uneven firing interval shows large torque variations of 200% above and 175% below mean torque.[2]

Cross-section of a VR6 engine

From 1991-present, Volkswagen has produced narrow angle VR6 engines with V-angles of 10.5 and 15 degrees. These engines use a single cylinder head shared by both banks of cylinders, in a design similar to the 1922-1976 Lancia V4 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 50 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.

1984-1999 Nissan VG30E 60-degree engine

A V-angle of 60 degrees is the optimal configuration for V6 engines regarding engine balance.[3] 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 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 in order to reduce vibration. More recent designs often use a three-throw crankshaft with 'flying arms' between the crankpins. The flying arms allow an even firing interval of 120 degrees to be achieved, and also used as balancing masses for the crankshaft.[4]^(p16) Combined with a pair of heavy counterweights on the crankshaft ends, flying arms can eliminate the primary imbalance and reduce the vibration from the secondary imbalance to acceptable levels.[4]^(pp13–16) The engine mounts can be designed to absorb these remaining vibrations.[4]^:{{{1}}}

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 engine size being a cube shape, making the engine easier to fit either longitudinally or transversely in the engine compartment.

1996-2005 Rover KV6 90-degree engine[5]

Many manufacturers, particularly American ones, built V6 engines with a V-angle of 90 degrees based on their existing 90-degree V8 engines. Such configurations were easy to design by removing two cylinders and replacing the V8 engine's four-throw crankshaft with a three-throw crankshaft. This reduced design costs, allowed the new V6 to share components with the V8 engine, and sometimes allowed manufacturers to build the V6 and V8 engines on the same production line.

The downsides of a 90 degree design are a wider engine which is more vibration-prone than a 60 degree V6. The initial 90 degree V6 engines (such as the Buick Fireball V6 engine) had three shared crankpins arranged at 120 degrees from each other, due to their origins from the V8 engines. This resulted in an uneven firing order, with half of the cylinders using a firing interval of 90 degrees and other half using an interval of 150 degrees. The uneven firing intervals resulted in rough-running engines with unpleasant harmonic vibrations at certain engine speeds.

Several modern 90 degree V6 engines reduce the vibrations using split crankpins offset by 30 degrees between piston pairs, which creates an even firing interval of 120 degrees for all cylinders.[3] For example, the 1977 Buick 231 "even-fire" V6 engine was an upgraded version of the Buick Fireball engine with a split-pin crankshaft to reduce vibration by achieving an even firing order.[4]^(p16)[6] Such a 'split' crankpin is weaker than a straight one, but modern metallurgical techniques can produce a crankshaft that is adequately strong.

A balance shaft and/or crankshaft counterweights can be used to reduce vibrations in 90 degree V6 engines.[4]^(pp14–44)

At first glance, 120 degrees might seem to be the optimal V-angle for a V6 engine, since pairs of pistons in alternate banks can share crank pins in a three-throw crankshaft and the combustion forces are balanced by the firing interval being equal to the angle between the cylinder banks. A 120 degree configuration, unlike the 60 degree or 90 degree configurations, would not require crankshafts with flying arms, split crankpins, or seven main bearings to be even-firing. However, the primary imbalance caused by odd number of cylinders in each bank still remains in a 120 degree V6 engine. This differs from the perfect balance achieved by a 90 degree V8 engine with a commonly used crossplane crankshaft, because the inline-four engine in each bank of the V8 engine does not have this primary imbalance.

A 120 degree design also results in a large width for the engine, being only slightly narrower than a flat-six engine (which does not have the balance problems of the V6 engine). Therefore the flat-six engine has been used in various automobiles, whereas use of the 120 degree V6 engine has been limited to a few truck and racing car engines.

Other angle V6 engines are possible but can suffer from severe vibration problems unless very carefully designed. Notable V-angles include:

• 45 degrees — EMD 567 and EMD 645 locomotive, marine and stationary Diesel engines. These engines were based on V8 and V16 engines which also used a V-angle of 45 degrees.
• 54 degrees — 1994-2004 General Motors 54-degree automotive engine. A slightly smaller than usual V-angle was used to reduce the width of the engine, allowing it to be used in small transverse-engine front-wheel drive cars.
• 65 degrees — 1956-1975 Ferrari Dino automobile engine. The V-angle was increased from the then-common 60 degree angle to allow larger carburetors to be used (for potentially higher power in race tuning). Crankpins with a offset of 55 degrees within every pair of cylinders were used to achieve the even firing interval of a 60 degree V6 engine. The 2009-present Nissan-Renault V9X automobile engine also used a 65 degree bank angle, to allow a turbocharger to fit between the cylinder banks.
• 72 degrees — Mercedes-Benz Bluetec automotive diesel engine. This engine uses crank pins offset by 48 degrees, to achieve an even firing interval.
• 75 degrees — 1992-2004 Isuzu V engine used in the Isuzu Rodeo and Isuzu Trooper. These engines were produced in both SOHC and DOHC versions. A 75 degree V6 engine is also used by the 2016-present Honda NSX.
• 80 degrees — 1988 Honda RA168-E engine used in the McLaren MP4/4 Formula One racing car.

Mercedes-Benz V6 DTM engine

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.[11][12] 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.[13][14]

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.[15][16] 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).[17] 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.[18]^{(pp138–141)} 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 sportscar 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.[19] 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, Lotus 95T, Lotus 98T, Lotus 99T and Lotus 100T.

The Nissan GTP ZX-Turbo and Nissan NPT-90 competed in the IMSA sports car prototype category from 1985-1994 and used a turbocharged V6 engine loosely based on the Nissan VG30ET production car engine.[20][21] The Nissan 300ZX used a similar engine to compete in the 1996-1997 All Japan Grand Touring Car Championship (now known as the 'Super GT' championship).[22][23]

Downsizing to V6 engines in open-wheeler racing became more common since the early 2010s:

• the IndyCar Series switched to turbocharged V6 engines in 2012.
• the GP3 Series switched to naturally aspirated V6 engines in 2013.
• the Formula One World Championship switched to turbocharged V6 engines in 2014.
• the FIA Formula 2 Championship (formerly known as the GP2 Series) switched to turbocharged V6 engines in 2018.
• the FIA Formula 3 Championship (created from the merger of the GP3 Series and the FIA Formula 3 European Championship) began using naturally aspirated V6 engines from 2019.