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A V6 engine is a V engine with six cylinders mounted on the crankshaft in two banks of three cylinders, usually set at either a 60 or 90 degree angle to each other. The V6 is one of the most compact engine configurations, usually ranging from 2.0 L to 4.3 L displacement (however, much larger examples have been produced for use in trucks), shorter than the inline 4 and more compact than the V8 engine. Because of its short length, the V6 fits well in the widely used transverse engine front-wheel drive layout. It is becoming more common as the space allowed for engines in modern cars is reduced at the same time as power requirements increase, and has largely replaced the inline 6, which is nearly twice as long - too long to fit in many modern engine compartments - and the V8, which is larger, more expensive, and has poorer fuel economy. The V6 engine has become widely adopted for medium-sized cars, often as an optional engine where an inline 4 is standard, or as a standard engine where a V8 is a higher-cost performance option.
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Applications
The V6 is commercially successful in mid-size cars in the modern age of high fuel prices and price sensitive consumers because it is less expensive to build and has better fuel consumption than the V8, while being smoother in large sizes than the inline 4, which develops increasingly serious vibration problems in larger engines. The wider 90° V6 will fit in an engine compartment designed for a V8, providing a low-cost alternative to the V8 in an expensive car, while the narrower 60° V6 will fit in most engine compartments designed for an I4, proving a more powerful and smoother alternative engine to the four. While not perfectly smooth, the V6 is smoother than the I4 and adequately smooth for the average consumer. Buyers of luxury and/or performance cars who are not price sensitive or fuel economy minded might prefer an inline 6, which has comparable fuel economy and power but better smoothness, a flat 6 which combines better smoothness and often higher power with adequate fuel economy, or a V8 which has higher power, but worse fuel economy.
Recent forced induction V6 engines have delivered horsepower and torque output comparable to contemporary larger displacement, naturally aspirated V8 engines, while reducing fuel consumption and emissions, such as the Volkswagen Group's 3.0 TFSI which is supercharged and directly injected, and Ford Motor Company's turbocharged and directly injected EcoBoost V6, both of which have been compared to Volkswagen's 4.2 V8 engine.
Modern V6 engines commonly range in displacement from 2.0 to 4.3 L (120 to 260 cu in), though larger and smaller examples have been produced, such as the 1991 Mazda MX3, and the Rover KV6 engine.
History
Some of the first V6-powered automobiles were built in 1905 by Marmon. This firm became something of a V-engine specialist; beginning with V2 engines, then V4s, V6s, V8s, and, in the 1930s, a V16 engine. Marmon was one of the few automakers of the world to offer a V16-powered automobile.
From 1908 to 1913 the Deutz Gasmotoren Fabrik produced benzene electric train sets (Hybrid) which used a V6 as generator engine.
Another V6-powered car was designed in 1918 by Leo Goosen for Buick Chief Engineer Walter L. Marr. Only one prototype Buick V6 car was built in 1918; it was long used by the Marr family.
The first series-production V6 was introduced by Lancia in 1950 with the Lancia Aurelia model. Lancia sought a smoother and more powerful engine that would fit into an existing narrow engine bay. A Lancia engineer, Francesco De Virgilio, began analyzing the vibration of alternative V-angles for a V6 engine in 1943. He found that a V6 with its cylinders positioned at a 60° V-angle could be made uniquely smooth-running in comparison with other possible V-angles. There was resistance to his conclusion, because the V6 was a virtually unknown engine type in the 1950s. His design featured four main bearings and six crankpins, resulting in evenly spaced firing intervals and low vibrations.
Other manufacturers took note and soon other V6 engines were designed. In 1959, General Motors' GMC Truck division introduced a new 60-degree heavy-duty 305 in3 (5.0 L) gasoline-fueled 60° V6 for use in their pickup trucks and Suburbans; this engine design was later enlarged to 478 in3 (7.8 L) for heavy truck and bus use. The use of the sweet spot of 60 degrees' V-angle maximized power while minimizing vibration and exterior dimensions of the engine. In short, GMC introduced a compact V6 design at a time when the straight-six engine was considered the pinnacle of 6-cylinder design.
1962 saw the introduction of the Buick Special, which offered a new 90° V6 with uneven firing intervals that was derived from—and shared some parts commonality with—a small Buick V8 engine of the period. To save design time and expense, it was built much like a V8 that had two cylinders chopped off. The combination of a 90° V-angle with only three crank pins—set at 120° apart, with opposing cylinders sharing a crank pin as most V8 engines do—the cylinders fired alternatively at 90 and 150° of crankshaft rotation. This uneven firing caused harmonic vibrations in the drive train that were perceived as a rough-running engine by the buyers. GM sold the engine tooling to Kaiser-Jeep in 1967; later, as a result of the 1973 oil crisis, GM repurchased the tooling in 1974. In 1977, Buick introduced a split pin crankshaft to implement an even-fire version of this engine in which cylinders fired consistently every 120°.
Balance and smoothness
The V6 does not have the inherent freedom from vibration that the inline-six and flat-six have, but it can be modeled as two separate straight-3 engines sharing a crankshaft. Counterweights on the crankshaft and a counter rotating balance shaft are required to compensate for the first order rocking motions.
Straight engines with an odd number of cylinders are inherently unbalanced because there are always an odd number of pistons moving in one direction while a different number move the opposite direction. This causes an end-to-end rocking motion at crankshaft speed in a straight-three engine. V6 designs will behave like two unbalanced three-cylinder engines running on the same crankshaft unless steps are taken to mitigate it, for instance by using offset journals or flying arms on the crankshaft or a counter-rotating