A V12 engine is a V engine with 12 cylinders mounted on the crankcase in two banks of six cylinders, usually but not always at a 60° angle to each other, with all 12 pistons driving a common crankshaft.
Since each cylinder bank is essentially a straight-6, this configuration has perfect primary and secondary balance no matter which V angle is used and therefore needs no balance shafts. A V12 with two banks of six cylinders angled at 60°, 120° or 180° (with the latter configuration usually referred to as a flat-12) from each other has even firing with power pulses delivered twice as often per revolution as a straight-6. This allows for great refinement in a luxury car. In a racing car, the rotating parts can be made much lighter and thus more responsive, since there is no need to use counterweights on the crankshaft as is needed in a 90° V8 and less need for the inertial mass in a flywheel to smooth out the power delivery. In a large displacement, heavy-duty engine, a V12 can run slower than smaller engines, prolonging engine life.
In October 1913 Louis Coatalen, chief engineer of the Sunbeam car company entered a V12 powered car in the Brooklands short and long handicap races. The engine displaced 9,048 cc, with bore and stroke of 80 x 150 mm. An aluminium crankcase carried two blocks of three cylinders along each side, with a 60 degree included angle. The cylinders were of iron, with integral cylinder heads with L-shaped combustion chambers. Inlet and exhaust valves were operated by a central camshaft in the vee. Valve clearance was set by grinding the relevant parts, the engine lacking any easy means of adjustment. This pointed to Coatalen’s ultimate aim of using the new V12 as an aero engine, where any adjustment method that could go wrong in flight was to be avoided. As initially built the V12 was rated at 200 bhp (150 kW) at 2,400 rpm, weighing about 750 pounds (340 kg). The engine powered the car (named ‘Toodles V’ (for Coatalen’s wife Olive’s pet name) to several records in 1913 and 1914.
In automobiles, V12 engines have not been common due to their complexity and cost. They are used almost exclusively in expensive sports and luxury cars because of their power, smoother operation and distinctive sound.
Prior to World War II, 12-cylinder engines were found in many luxury models, including cars from: Packard 1916 to 1923, Daimler 1926 to 1937, Hispano-Suiza 1931, Cadillac 1931, Auburn 1932, Franklin 1932, Lincoln 1932, Rolls-Royce 1936, and Pierce-Arrow also 1936.
Until the general adoption of vibration isolating engine mounts in the 1930s, vehicles with 8-, 12-, and 16-cylinders provided higher levels of refinement.
Packard's 1916 "Twin Six" is widely regarded as the first production V12 engine. With a list price of US$1,000, the Auburn was the lowest priced V12 car ever (unadjusted for inflation). Production cost savings were achieved by using horizontal valves which, however, did not result in an efficient and powerful combustion chamber. Between 1916 and 1921, there was a vogue of V12s, during which National (Indianapolis) copied the Packard engine, and Weidely Motors (also of Indianapolis) offered a proprietary engine. Soon after the end of World War I, Lancia offered a 22° V12, Fiat had a 60° model 520 (1921-2), British truck manufacturer Ensign announced a V12 that did not materialize, and in 1926, Daimler (Britain) offered the first of a full range of sleeve valve Double Sixes, 7,136 cc, 3,744 cc, 5,296 cc and 6,511 cc versions remaining available until 1937 In 1927 more entered the market from, Cadillac, Franklin, Hispano-Suiza, Horch, Lagonda, Maybach, Packard, Rolls, Tatra, Voisin, and Walter offering V12 engines. Cadillac (from 1930 to 1940) and Marmon (1931–1933) even developed V16 engines.
Improvements in combustion chamber design and piston form enabled lighter V8 engines to surpass the V12 in power starting from the 1930s; only the smaller, H-Series Lincoln V-12 remained after WWII and it was replaced by a V8 in 1949. Similarly, as they seemed excessive for the postwar market in Europe, production of V12-engined-cars was very limited until the 1960s.
Ferrari has traditionally reserved their top V12 engine for their top-of-the line luxury sports coupes since 1949. Ferrari's closest rival, Lamborghini has also used the V12 configuration for many of its road cars since the company's inception in 1963. In 1972, Jaguar came out with the XJ12, equipped with a 5.3 litre V12, which continued (after revisions in 1993) until the 1996 model year, after which the marque discontinued the twelve-cylinder engine.
German manufacturer BMW returned to V12 designs for its 7-Series sedan in model year 1986, forcing Mercedes-Benz to follow suit in 1991. While BMW sells far fewer V12-engined 7-Series vehicles than V8 versions, the V12 retains popularity in the US, China, and Russia, as well as maintaining the marque's prestige in the luxury vehicle market segmentThe BMW-designed V12 also appears in Rolls-Royce cars, while the Mercedes engine is also seen in Maybach cars. In their full-sized sedans sold in Canada and the USA, Mercedes and BMW have mid-displacement V8s for the entry-level trims, while having the V12 as the flagship vehicle of the brand.For their most expensive Mercedes-Benz nameplates (S-Class, CL-Class, and SL-Class), there are V8-engined AMG models (55, 63) that have comparable power to their V12-powered cars (600).
In 1997, Toyota equipped their Century Limousine with a 5.0 L DOHC V12 (model # 1GZ-FE), making it the first and only Japanese production passenger car so equipped.
TVR made and tested a 7.7 L V12 called the Speed Twelve, but the project was scrapped after the car it was designed for was deemed too powerful for practical use. The only British marques currently using a V12 configuration are Aston Martin — whose Cosworth-developed engine was authorized during the company's ownership by Ford Motor Company — and Rolls-Royce.
In 2009, China FAW Group Corporation equipped their Hongqi HQE with a 6.0 L DOHC V12 (model # CA12VG), making it the first and only Chinese production passenger car so equipped.
Most production V12 engines in road cars have an even firing order, with the uneven-firing exceptions such as Aston Martin 5.9L V12 and Mercedes-Benz M275 AMG V12s.
In 2008 Audi launched their Q7 model with a 5.9-litre V12 twin-turbo diesel engine, making it the first production passenger car so equipped. The engine also appeared in the R8 V12 TDI concept car.
Tatra used a 17.6 L (1,070 cu in) air-cooled naturally aspirated V12 diesel engine in many of their trucks; for instance, the Tatra T813 and uses 19 L air-cooled naturally aspirated or turbo V12 diesel engine in Tatra T815. Some large trucks have been fitted with twin V12s that drive a common shaft, although this is often advertised as a V24.
GMC produced a large gasoline-burning V12 from 1960 to 1965 for trucks, the "Twin-Six"; it was basically GMC's large-capacity truck 351 V6, doubled, with four rocker covers and four exhaust manifolds. Fifty-six major parts are interchangeable between the Twin-Six and all other GMC V6 engines to provide greater parts availability and standardization. Its engine displacement was 702 cu in (11.50 L), and while power was not too impressive at 250 hp (190 kW), torque was 585 lb·ft (793 N·m). For firetrucks the rev limiter was increased to produce 299 hp (223 kW) at 3000 rpm and torque was increased to 630 lb·ft (850 N·m) at 1600-1900 rpm. It was possibly the last gasoline engine used in heavy trucks in the U.S.
Detroit Diesel produced their Series 53, 71, 92, and 149 engines as V-12s, among other configurations.
V12 engines used to be common in Formula One and endurance racing. From 1965 to 1980, Ferrari, Weslake, Honda, BRM, Maserati, Matra, Delahaye, Peugeot, Delage, Alfa Romeo, Lamborghini and Tecno used 12-cylinder engines in Formula One, either V12 or Flat-12, but the Ford (Cosworth) V8 had a slightly better power-to-weight ratio and less fuel consumption, thus it was more successful despite being less powerful than the best V12s. During the same era, V12 engines were superior to V8s in endurance racing, reduced vibrations giving better reliability. In the 1990s, Renault V10 engines proved their superiority against the Ferrari and Honda V12s and the Ford V8. The last V12 engine used in Formula One was the Ferrari 044, on the Ferrari 412T2 cars driven by Jean Alesi and Gerhard Berger in 1995.
In the late 1960s Nissan used a V12 in the Japanese Grand Prix and again in the early 1990s Group C races.
At the Paris motor show 2006 Peugeot presented a new racing car, as well as a luxury saloon concept car, both called 908 HDi FAP and 908 RC and fitted with a V12 Diesel engine producing around or even surpassing 700 PS (515 kW; 690 hp). This took part in the 24 Hours of Le Mans 2007 race, with a podium finish and very competitive performance, coming in second place after the similarly conceived Audi R10 TDI V12 Diesel originally developed for the 2006 season.
The V12 is a common configuration for tank and other armoured fighting vehicles (AFVs). Some examples are: