Multi-valve

Multi-valve geometry allows the spark plug to be ideally located within the combustion chamber for optimal flame propagation.

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 (both desirable traits), it has been questioned whether a five-valve configuration gives a cost-effective benefit over four-valve designs.

After making five-valve Genesis engines for several years, Yamaha has since reverted to the cheaper four-valve design.

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.

Rotary valves also offer improved engine breathing and high rev performance but these were never very successful.

In April 1913, on the Brooklands racetrack in England, a specially built L76 called "la Torpille" (torpedo) beat the world speed record of 170 km/h.

[1] Robert Peugeot also commissioned the young Ettore Bugatti to develop a GP racing car for the 1912 Grand Prix.

40/60 GP was a fully working early racing car prototype made by the company now called Alfa Romeo.

[6][7][8] The mono block White Motor Car engine developed 72 horsepower and less than 150 were built, only three are known to exist today.

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.

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.

In 1931 the Stutz Motor Company introduced a 322 cid (5.3-liter) dual camshaft 32-valve straight-8 with 156 bhp (116 kW) at 3900 rpm, called DV-32.

[15][16] The 1935 Duesenberg SJ Mormon Meteor's engine was a 419.6 cid (6.9-liter) straight-8 with DOHC, 4 valves per cylinder and a supercharger.

Debuting at the 1968 Japanese Grand Prix in the original 300 PS (221 kW; 296 hp) 3.0-liter version the Toyota 7 engine participated in endurance races as a 5.0-liter (4,968 cc) non-turbo V8 with DOHC and 32-valves.

All of these, although mass-produced, are also of relatively limited production, so it is argued that the first widely available and popularly priced mass-production car with a four valve per cylinder engine was the 1973 Triumph Dolomite Sprint.

This Triumph used an in-house developed SOHC 16-valve 1,998 cc (122 ci) straight-4 engine that produced 127 bhp (47.6 kW/liter, 1.10 bhp/cid) at introduction.

Four valves per cylinder were added for the 1982 308 and Mondial Quattrovalvole, bringing power back up to the pre-FI high of 245 hp (183 kW) .

The cylinder head was developed by Yamaha Motor Corporation and was built at Toyota's Shimayama plant.

While originally conceived of as a two-valve design, Toyota and Yamaha changed the 4A-GE to a four-valve after a year of evaluation.

The Ford design uses one spark plug per cylinder located in the centre, but the Mercedes design uses two spark plugs per cylinder located on opposite sides, leaving the centre free to add a direct-to-cylinder fuel injector at a later date.

The V12 engines of many World War II fighter aircraft also used a SOHC configuration with four valves for each cylinder.

Pushrod multi-valve systems are common on diesels because they need to be able to meet emissions standards, but also produce more low-end torque.

The Harley-Davidson Milwaukee Eight engine, introduced in 2016, uses four-valves per cylinder driven by pushrods and a single in-block camshaft.

Examples of motorcycles with multivalve-engines include: The Yamaha XT660 single once had five valves per cylinder, but a subsequent redesign reduced the valve-count to four.

[33] The V12 engines of many World War II fighter aircraft used a SOHC configuration with four valves for each cylinder.

This liquid-cooled turbocharged 2.0-liter (1,991 cc) DOHC 16-valve straight-4 diesel engine uses common rail direct fuel injection and delivers 168 bhp (125 kW; 170 PS) at 3,880 rpm (62.0 kW/liter).

In 1905 car builder Delahaye had experimented with a DOHC marine racing engine with six valves per cylinder.

[34] An example of modern multi-valve engines for small boats is the Volvo Penta IPS Series.

These joystick-operated seawater-cooled inboard diesel engines use combined charging (turbo and supercharger, except IPS450) with aftercooler, common rail fuel injection and DOHCs with hydraulic 4-valve technology.