Multi-valve


A multi-valve or multivalve four-stroke internal combustion engine is one where each cylinder has more than two valves – more than the minimum required of one of each, for the purposes of air and fuel intake, and venting exhaust gases. Multi-valve engines were conceived to improve one or both of these, often called "better breathing", and with the added benefit of more valves that are smaller, thus having less mass in motion, may also be able to operate at higher revolutions per minute than a two-valve engine, delivering even more intake an/or exhaust per unit of time, thus potentially more power.

Multi-valve rationale

Multi-valve engine design

A multi-valve engine design has three, four, or five poppet valves per cylinder, to achieve greater performance. In automotive engineering, any four-stroke internal combustion engine needs at least two valves per cylinder: one for intake of air, and another for exhaust of combustion gases. Adding more valves increases valve area, which improves the flow of intake and exhaust gases, thereby enhancing combustion, volumetric efficiency, and power output. Multi-valve geometry allows the spark plug to be ideally located within the combustion chamber for optimal flame propagation. Multi-valve engines tend to have smaller valves that have lower reciprocating mass, which can reduce wear on each cam lobe, and allow more power from higher rpm without the danger of valve float. Some engines are designed to open each intake valve at a slightly different time, which increases turbulence, improving the mixing of air and fuel at low engine speeds. More valves also provide additional cooling to the cylinder head.
Disadvantages of multi-valve engines are a greater parts count, and thus an increase in manufacturing and possibly also maintenance costs, and a potential increase in oil consumption due to the greater number of valve stem seals.
Most multi-valve engines are dual overhead camshaft designs, but some single overhead camshaft uses fork-shaped rocker arms, so that its single overhead camshaft can drive two valves at once, so that fewer cam lobes will be needed in order to reduce manufacturing costs.
  • Three-valve cylinder head
This has a single large exhaust valve and two smaller intake valves. A three-valve layout allows better breathing than a two-valve head, but the large exhaust valve results in an rpm limit no higher than a two-valve head. The manufacturing cost for this design can be lower than for a four-valve design. The three-valve design was common in the late 1980s and early 1990s; and from 2004 the main valve arrangement used in Ford F-Series trucks, and Ford SUVs. The Ducati ST3 V-twin had 3-valve heads.
  • Four-valve cylinder head
This is the most common type of multi-valve head, with two exhaust valves and two similar inlet valves. This design allows similar breathing as compared to a three-valve head, and as the small exhaust valves allow high rpm, this design is very suitable for high power outputs.
  • Five-valve cylinder head
Less common is the five-valve head, with two exhaust valves and three inlet valves. All five valves are similar in size. This design allows excellent breathing, and, as every valve is small, high rpm and very high power outputs are theoretically available. Although, compared to a four-valve engine, a five-valve design should have a higher maximum rpm, and the three inlet ports should give efficient cylinder-filling and high gas turbulence, it has been questioned whether a five-valve configuration gives a cost-effective benefit over four-valve designs. The rise of direct injection may also make five-valve heads more difficult to engineer, as the injector must take up some space on the head. After making five-valve Genesis engines for several years, Yamaha has since reverted to the cheaper four-valve design.
Examples of the five-valve engines are the various 1.8 L 20vT engines manufactured by AUDI AG, the later versions of the Ferrari Dino V8, and the 1.6 L 20-valve 4A-GE engine made by Toyota in collaboration with Yamaha.
  • Beyond five valves
For a cylindrical bore and equal-area sized valves, increasing the number of valves beyond five decreases the total valve area. The following table shows the effective areas of differing valve quantities as proportion of cylinder bore. These percentages are based on simple geometry and do not take into account orifices for spark plugs or injectors, but these voids will usually be sited in the "dead space" unavailable for valves. Also, in practice, intake valves are often larger than exhaust valves in heads with an even number of valves-per-cylinder:
  • 2 = 50%
  • 3 = 64%
  • 4 = 68%
  • 5 = 68%
  • 6 = 66%
  • 7 = 64%
  • 8 = 61%

    Alternative technologies

and supercharging are technologies that also improve engine breathing, and can be used instead of, or in conjunction with, multi-valve engines. The same applies to variable valve timing and variable-length intake manifolds. Rotary valves also offer improved engine breathing and high rev performance but these were never very successful. Cylinder head porting, as part of engine tuning, is also used to improve engine performance.

Cars and trucks

Before 1914

The first motorcar to use an overhead camshaft engine was the Marr in 1902, which had a single-cylinder engine with a single overhead camshaft and two valves per cylinder. The 1908 Ariès VT race cars had 1.4-liter supercharged single-cylinder engines with four desmodromic valves per cylinder. The 1910 Isotta Fraschini Tipo KM had a 10.6-liter single overhead camshaft straight-4 with four valves per cylinder producing and was one the first engines to have fully enclosed overhead valve gear.
The first motorcar in the world to have an engine with two overhead camshafts and four valves per cylinder was the 1912 Peugeot L76 Grand Prix race car designed by Ernest Henry. Its 7.6-liter monobloc straight-4 with modern hemispherical combustion chambers produced, which is. In April 1913, on the Brooklands racetrack in England, a specially built L76 called "la Torpille" beat the world speed record of 170 km/h. Robert Peugeot also commissioned the young Ettore Bugatti to develop a GP racing car for the 1912 Grand Prix. This chain-driven Bugatti Type 18 had a 5-liter straight-4 with SOHC and three valves per cylinder. It produced approximately at 2800 rpm and could reach. The three-valve head would later be used for some of Bugatti's most famous cars, including the 1922 Type 29 Grand Prix racer and the legendary Type 35 of 1924. Both Type 29 and Type 35 had a 2-liter SOHC 24-valve NA straight-8 that produced per cubic inch.

Between 1914 and 1945

was a fully working early racing car prototype made by the company now called Alfa Romeo. Only one example was built in 1914, which was later modified in 1921. This design of Giuseppe Merosi was the first Alfa Romeo DOHC engine. It had four valves per cylinder, 90-degree valve angle and twin-spark ignition. The GP engine had a displacement of 4.5-liter and produced at 2950 rpm, and after modifications in 1921 at 3000 rpm. The top speed of this car was 88-93 mph. It wasn't until the 1920s when these DOHC engines came to Alfa road cars like the Alfa Romeo 6C.
In 1916, US automotive magazine Automobile Topics described a four-cylinder, four-valve-per-cylinder car engine made by Linthwaite-Hussey Motor Co. of Los Angeles, CA, USA: "Firm offers two models of high-speed motor with twin intakes and exhausts.".
Early multi-valve engines in T-head configuration were the 1917 Stutz straight-4, White Motor Car Model GL 327 CID Dual Valve Mononblock four, and 1919 Pierce-Arrow straight-6 engines. The standard flathead engines of that day were not very efficient and designers tried to improve engine performance by using multiple valves. The Stutz Motor Company used a modified T-head with 16 valves, twin-spark ignition and aluminium pistons to produce 80 bhp at 2400 rpm from a 360.8 cid straight-4. Over 2300 of these powerful early multi-valve engines were built. Stutz not only used them in their famous Bearcat sportscar but in their standard touring cars as well. The mono block White Motor Car engine developed 72 horsepower and less than 150 were built, only three are known to exist today. In 1919 Pierce-Arrow introduced its 524.8 cid straight-6 with 24 valves. The engine produced 48.6 bhp and ran very quietly, which was an asset to the bootleggers of that era.
Multi-valve engines continued to be popular in racing and sports engines. Robert M. Roof, the chief engineer for Laurel Motors, designed his multi-valve Roof Racing Overheads early in the 20th century. Type A 16-valve heads were successful in the teens, Type B was offered in 1918 and Type C 16-valve in 1923. Frank Lockhart drove a Type C overhead cam car to victory in Indiana in 1926.
Bugatti also had developed a 1.5-liter OHV straight-4 with four valves per cylinder as far back as 1914 but did not use this engine until after World War I. It produced appr. 30 bhp at 2700 rpm. In the 1920 Voiturettes Grand Prix at Le Mans driver Ernest Friderich finished first in a Bugatti Type 13 with the 16-valve engine, averaging 91.96 km/h. Even more successful was Bugattis clean sweep of the first four places at Brescia in 1921. In honour of this memorable victory all 16-valve-engined Bugattis were dubbed Brescia. From 1920 through 1926 about 2000 were built.
Peugeot had a triple overhead cam 5-valve Grand Prix car in 1921.
Bentley used multi-valve engines from the beginning. The Bentley 3 Litre, introduced in 1921, used a monobloc straight-4 with aluminium pistons, pent-roof combustion chambers, twin spark ignition, SOHC, and four valves per cylinder. It produced appr. 70 bhp. The 1927 Bentley 4½ Litre was of similar engine design. The NA racing model offered 130 bhp and the 1929 supercharged 4½ Litre reached 240 bhp. The 1926 Bentley 6½ Litre added two cylinders to the monobloc straight-4. This multi-valve straight-6 offered 180–200 bhp. The 1930 Bentley 8 Litre multi-valve straight-6 produced appr. 220 bhp.
In 1931 the Stutz Motor Company introduced a 322 cid dual camshaft 32-valve straight-8 with 156 bhp at 3900 rpm, called DV-32. The engine offered 0.48 bhp per cubic inch. About 100 of these multi-valve engines were built. Stutz also used them in their top-of-the-line sportscar, the DV-32 Super Bearcat that could reach 100 mph.
The 1935 Duesenberg SJ Mormon Meteor's engine was a 419.6 cid straight-8 with DOHC, 4 valves per cylinder and a supercharger. It achieved 400 bhp at 5,000 rpm and 0.95 bhp per cubic inch.
The 1937 Mercedes-Benz W125 racing car used a supercharged 5.7-liter straight-8 with DOHC and four valves per cylinder. The engine produced 592-646 bhp at 5800 rpm and achieved 1.71-1.87 bhp per cubic inch. The W125 top speed was appr. 200 mph.