Multi-valve: Difference between revisions

[[File:Nissan VQ35DE 005.jpg|250px|thumb|A [[cylinder head]] of a four [[Poppetpoppet valve|valve]] engine.<br />( [[Nissan VQ engine]] )engine]]

A multi-valve engine design has three, four, or five [[poppet valve|valves]] per cylinder to achieve improved performance. In [[automotive engineering]], any four-stroke [[internal combustion engine]] needs at least two valves per cylinder: one for ''intake'' of air (and often fuel<ref name=fuel/>), and another for ''exhaust'' of combustion gases. Adding more valves increases valve area and improves the flow of intake and exhaust gases, thereby enhancing [[combustion]], [[volumetric efficiency]], and [[Engine efficiency|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 [[revolutions per minute|RPM]] without the danger of [[Valvevalve float|valve bounce]]. 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. The disadvantages of multi-valve engines are an increase in manufacturing cost and a potential increase in oil consumption due to the greater number of valve stem seals. Some [[SOHC]] multi-valve engines (such as the [[Mazda B engine#B8|Mazda B8-ME]]) use a single fork-shaped rocker arm to drive two valves (generally the exhaust valves) so that fewer cam lobes will be needed in order to reduce manufacturing costs.{{citation needed|date=April 2014}}

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 (both desirable traits), 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 [[Yamaha Genesis engine|Genesis engines]] for several years, [[Yamaha Motor Company|Yamaha]] has since reverted back to the cheaper four-valve design.

Examples of the five-valve engines are the various [[List of Volkswagen Group petrol engines#1.8 R4 20vT (EA113/EA827)|1.8 L 20vT engines]] manufactured by AUDI AG, the later versions of the [[Ferrari]] [[Ferrari Dino engine|Dino V8]], and the 1.6 L [[Toyota A engine#4A-GE (20-valve)|20-valve 4A-GE]] engine made by Toyota in collaboration with Yamaha.

[[Turbocharging]] and [[Supercharger|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 [[Variablevariable-length intake manifold|variable-length intake manifolds]]s. [[Rotary valve#Use in engine design|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.

There is much discussion about which was the first 'mass-produced' car to use an engine with four valves per cylinder. For six cylinder engines, and considering special versions of mass-produced cars, the first appears to have been the 1969 [[Nissan Skyline]], using the Nissan [[Nissan S20 engine|S20]] six cylinder DOHC four-valve engine. This engine was also fitted to [[Nissan Fairlady]] Z432 racing edition.

For a four -cylinder engine, the first mass-produced car using a four valves per cylinder engine was the British [[Ford Escort RS1600]], this car used the Cosworth BDA engine which was a Ford 'Kent' block with a [[Cosworth]] 16 valve twin cam cylinder head. The car went on to become a rallying legend in the 1970s winning many domestic and World Championship events. Other cars claiming to be first are the [[Jensen Healey]], launched in 1972 which used a [[Lotus 907]] belt-driven DOHC 16-valve 2-liter straight-4 producing 140&nbsp;bhp (54.6&nbsp;kW/liter, 1.20&nbsp;bhp/cid). 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 [[Dolomite Sprint|Triumph Dolomite Sprint]]. This Triumph used an in-house developed SOHC 16-valve 1,998 cc (122 ci) straight-4 engine that produced 127&nbsp;bhp (47.6&nbsp;kW/liter, 1.10&nbsp;bhp/cid) at introduction.

* 1978 [[Honda CX series|Honda CX500]], a 498 cc SOHC, pushrod actuated OHV, 4-valve per cylinder V-twin; 1982 [[Honda CX500#CX500 Turbo|CX500 Turbo]] was the first factory multi-valve [[Turbochargerturbocharger|turbocharged]] motorcycle.

Long after the King-Bugatti "U-16" aviation engine used them, shortly before World War II, the [[Junkers]] aviation firm began production of the Third Reich's most-produced military aviation engine (68,000+ produced), the 1936-designed, 35-litre displacement, inverted-V12, liquid-cooled [[Junkers Jumo 211]], which used a three-valve cylinder head design<ref>[http://www.enginehistory.org/German/Jumo%20211/j26.jpg German language illistrationillustration of Jumo 211 three-valve design]</ref> inherited from Junkers' first inverted V12 design, the 1932-origin [[Junkers Jumo 210]]<ref>{{cite web |url=https://www.flightglobal.com/pdfarchive/view/1937/1937%20-%202509.html?search=three%20valve |title=Flight Magazine, September 9, 1937 |author=<!--Not stated--> |date=September 9, 1937 |page=265 |website=flightglobal.com |publisher=Flightglobal Archive |access-date=March 15, 2017 |quote=At the recent international meeting at Zürich, several of the successful German machines were fitted with the new Junkers 210 petrol engine...'''Three valves per cylinder are provided, two inlets and one exhaust,''' operated by push rods and rockers from a single camshaft.}}</ref> — this was carried through into the later, more powerful 1940-origin [[Junkers Jumo 213]], produced through 1945, the production versions of which (the Jumo 213A and -E subtypes) retained the Jumo 211's three-valve cylinder head design.<ref>{{cite web |url=http://www.enginehistory.org/German/Jumo213/Jumo213.shtml |title=The Junkers Jumo 213 Engine |last=Culy |first=Doug |date=April 4, 2012 |website=enginehistory.org |publisher=Aircraft Engine Historical Society |access-date=March 15, 2017 |quote=The Jumo 213 had a three-valve head, but a four-valve head was in development for the “J” version. However, the Jumo 213A is documented as itself having superior high altitude performance at that particular point in time, although the DB 603 was later developed with equal or better features. |url-status=dead |archive-url=https://web.archive.org/web/20161221130406/http://www.enginehistory.org/German/Jumo213/Jumo213.shtml |archive-date=December 21, 2016 }}</ref>

<ref name=fuel>In direct injection engines - such as diesels and later petrol engines - fuel is delivered to the chamber directly via the injector rather than through a valve. In carburetted engines and indirect-injection engines the fuel is mixed with the air outside of the cylinder and both enter together via the intake valve. </ref>