Editing Straight-four engine

{{short description|Inline piston engine with four cylinders}}
[[File:Engine movingparts.jpg|thumb|Diagram of a [[DOHC]] straight-four engine]]
[[File:Ford-I4DOHC-engblock.jpeg|thumb|1989-2006 [[Ford I4 DOHC engine]] with the cylinder head removed]]
[[File:Nissan M9R Engine 03.JPG|thumb|2006-2009 [[Nissan_MR_engine#M9R|Nissan M9R]] diesel engine]]

A '''straight-four engine''' (also referred to as an '''inline-four engine''') is a four-cylinder [[Reciprocating engine|piston engine]] where cylinders are arranged in a line along a common crankshaft.

The majority of automotive four-cylinder engines use a straight-four layout<ref name="Nunney"/>{{refpage|pp. 13–16}} (with the exceptions of the [[flat-four engine]]s produced by Subaru and Porsche)<ref>{{cite web | url = http://www.porsche.com/canada/en/models/718/718-boxster/drive/performance/ | title = Performance: The new 718 Boxster | date = 2016 | publisher = Porsche | access-date = 2016-11-01}}</ref> and the layout is also very common in motorcycles and other machinery. Therefore the term "four-cylinder engine" is usually synonymous with straight-four engines. When a straight-four engine is installed at an inclined angle (instead of with the cylinders oriented vertically), it is sometimes called a [[Slant-4 engine|slant-four]].

Between 2005 and 2008, the proportion of new vehicles sold in the United States with four-cylinder engines rose from 30% to 47%.<ref>{{cite news| url=https://www.nytimes.com/2010/10/17/automobiles/autoreviews/17BUICK.html | work=The New York Times | first=James | last=Schembari | title=A Family Sedan Firing on Fewer Cylinders - 2010 Buick LaCrosse CX - Review | date=2010-10-15}}</ref><ref>{{cite news| url=https://www.nytimes.com/2010/08/15/automobiles/15FOUR.html | work=The New York Times | first=Lawrence | last=Ulrich | title=Four-Cylinder Engines Are Smaller, Quieter and Gaining New Respect | date=2010-08-13}}</ref> By the 2020 model year, the share for light-duty vehicles had risen to 59%.<ref>{{cite web|url=https://www.epa.gov/automotive-trends/explore-automotive-trends-data#DetailedData|title=Explore the Automotive Trends Data|accessdate=2021-11-25|date=November 2021}}</ref>

== Design ==
A four-stroke straight-four engine always has a cylinder on its power stroke, unlike engines with fewer cylinders where there is no power stroke occurring at certain times. Compared with a [[V4 engine]] or a [[flat-four engine]], a straight-four engine only has one [[cylinder head]], which reduces complexity and production cost.

=== Displacement ===
Petrol straight-four engines used in modern production cars typically have a displacement of {{convert|1.3|-|2.5|L|cuin|0|abbr=on}}, but larger engines have been used in the past, for example the 1927–1931 [[Bentley 4½ Litre]].

Diesel engines have been produced in larger displacements, such as a 3.2&nbsp;L turbocharged Mitsubishi engine (used the Pajero/Shogun/Montero SUV) and a 3.0&nbsp;L Toyota engine. European and Asian trucks with a [[gross vehicle weight rating]] between 7.5 and 18 tonnes commonly use inline four-cylinder diesel engines with displacements around 5&nbsp;litres.<ref>{{cite web |url=http://www.man-engines.com/datapool/mediapool/800/D0834_LKW_dt.pdf |title=4-Zylinder Reihenmotor für Nutzfahrzeuge. |access-date=2011-08-01 |url-status=dead |archive-url=https://web.archive.org/web/20110714024640/http://www.man-engines.com/datapool/mediapool/800/D0834_LKW_dt.pdf |archive-date=2011-07-14 }}</ref><ref>{{cite web |url=http://www.mantruckandbus.com/en/Products_and_solutions/MAN_Lkw/TGL/TGL.jsp |title=MAN Truck & Bus - TGL |access-date=2011-05-09 |url-status=dead |archive-url=https://web.archive.org/web/20110523132506/http://www.mantruckandbus.com/en/Products_and_solutions/MAN_Lkw/TGL/TGL.jsp |archive-date=2011-05-23 }}</ref><ref>{{cite web |url=http://www.vario-mobil.com/welcome%20to%20variomobil.html |title=VARIOmobil - Welcome to a lap of luxury coaches - recreation vehicles - motor homes |access-date=2011-05-09 |url-status=dead |archive-url=https://web.archive.org/web/20110827160415/http://www.vario-mobil.com/welcome%20to%20variomobil.html |archive-date=2011-08-27 }}</ref><ref>{{cite web |url=http://www.isuzucv.com/engines/4h_index.html |title=Isuzu Commercial Vehicles - Low Cab Forward Trucks - Commercial Vehicles - 4HK1-TC 5.2L Diesel Engine |access-date=2010-12-14 |url-status=dead |archive-url=https://web.archive.org/web/20101224200033/http://www.isuzucv.com/engines/4h_index.html |archive-date=2010-12-24 }}</ref><ref>{{cite web |url=http://www.isuzutruck.co.uk/downloads/specsheets/fseries/f110.210%20easyshift.pdf |title=Euro 4 'Forward' F11O.21O |access-date=2010-12-14 |url-status=dead |archive-url=https://web.archive.org/web/20101126070600/http://isuzutruck.co.uk/downloads/specsheets/fseries/f110.210%20easyshift.pdf |archive-date=2010-11-26 }}</ref><ref>{{cite web|url=http://www.hino-global.com/products/diesel_engines/index.html |title=Diesel Engines &#124; Products |publisher=Hino Global |access-date=2017-05-23}}</ref><ref>{{cite web |url=http://www.hino-global.com/pdf/catalog/Hino_500S_Catalog_LR.pdf |title=Hino 500 Series |access-date=2010-12-14 |url-status=dead |archive-url=https://web.archive.org/web/20101214123029/http://www.hino-global.com/pdf/catalog/Hino_500S_Catalog_LR.pdf |archive-date=2010-12-14 }}</ref> Larger displacements are found in locomotive, marine and stationary engines.

Displacement can also be very small, as found in [[kei car]]s sold in Japan. Several of these engines had four cylinders at a time when regulations dictated a maximum displacement of 550&nbsp;cc; the maximum size is currently at 660&nbsp;cc.

=== Primary and secondary balance ===
Straight-four engines with the preferred crankshaft configuration have perfect [[primary balance]].<ref name="Nunney">{{cite book|last=Nunney|first=M J|title=Light and Heavy Vehicle Technology|edition=4th|publisher= Butterworth-Heinemann|year=2006|isbn=0-7506-8037-7|ref=Nunney}}</ref>{{refpage|p. 12}} This is because the pistons are moving in pairs, and one pair of pistons is always moving up at the same time as the other pair is moving down.

However, straight-four engines have a [[Secondary balance|secondary imbalance]]. This is caused by the acceleration/deceleration of the pistons during the top half of the crankshaft rotation being greater than that of the pistons in the bottom half of the crankshaft rotation (because the connecting rods are not infinitely long). As a result, two pistons are always accelerating faster in one direction, while the other two are accelerating more slowly in the other direction, which leads to a secondary dynamic imbalance that causes an up-and-down vibration at twice crankshaft speed. This imbalance is common among all piston engines, but the effect is particularly strong on four-stroke inline-four because of the two pistons always moving together.

The strength of this imbalance is determined by the reciprocating mass, the ratio of connecting rod length to stroke, and the peak piston velocity. Therefore, small displacement engines with light pistons show little effect, and racing engines use long connecting rods. However, the effect [[quadratic growth|grows quadratically]] with engine speed (rpm).

=== Pulsations in power delivery ===
[[File:Reihenmotor Vier Zylinder 1-2-4-3.gif|thumb|Animation of an Inline-four engine]]
[[Four-stroke engine]]s with five or more cylinders are able to have at least one cylinder performing its power stroke at any given point in time. However, four-cylinder engines have gaps in the power delivery, since each cylinder completes its power stroke before the next piston starts a new power stroke. This pulsating delivery of power results in more vibrations than engines with more than four cylinders.

=== Usage of balance shafts ===
[[File:MMC Silent shafts.jpg|thumb |Mitsubishi Silent Shaft display]]

A [[balance shaft]] system is sometimes used to reduce the vibrations created by a straight-four engine, most often in engines with larger displacements. The balance shaft system was invented in 1911 and consists of two shafts carrying identical [[Eccentric (mechanism)|eccentric]] weights that rotate in opposite directions at twice the crankshaft's speed.<ref name="Nunney"/>{{refpage|pp. 42–44}} This system was patented by Mitsubishi Motors in the 1970s, introduced in the [[Mitsubishi Astron engine]] with the "Silent Shaft" name, and has since been used under licence by several other companies.<ref name="bbc1">{{cite web |url=http://www.bbc.com/autos/story/20140609-before-they-were-carmakers |title=Before they were carmakers |last=Carney |first=Dan |publisher=BBC |location=UK |date=2014-06-10 |access-date=2018-11-01}}</ref><ref name="PS-Jun89">{{cite magazine |last=Nadel |first=Brian |date=June 1989 |title=Balancing Act |magazine=Popular Science |page =52 }}</ref>

Not all large displacement straight-four engines have used balance shafts, however. Examples of relatively large engines without balance shafts include the 2.4 litre [[Citroën DS]] engine, the 2.6 litre [[Austin-Healey 100]] engine, the 3.3&nbsp;L [[Ford Model A (1927)]] engine and the 2.5&nbsp;L [[GM Iron Duke engine]]. Soviet/Russian [[Volga (automobile)|GAZ Volga]] and [[UAZ]] engines with displacements of up to 2.9 litres were produced without balance shafts from the 1950s to the 1990s, however these were relatively low-revving engines which reduces the need for a balance shaft system.<ref name="Nunney"/>{{refpage|pp. 40–44}}

== Usage in production cars ==
[[File:Fordsidevalve.jpg|thumb |1908–1941 [[Ford Model T]] engine]]
[[File:Alfa Romeo 1750 GTV engine.jpg|thumb|1970 [[Alfa Romeo Twin Cam engine]] ]]

Most modern straight-four engines used in cars have a displacement of {{convert|1.5|-|2.5|L|cuin|0|abbr=on}}. The smallest automotive straight-four engine was used in the 1963–1967 [[Honda T360]] kei truck and has a displacement of {{convert|356|cc|cid|abbr=on}}, while the largest mass-produced straight-four car engine is the 1999–2019 [[Mitsubishi_4M4_engine#4M41|Mitsubishi 4M41]] diesel engine which was used in the Mitsubishi Pajero and has a displacement of {{convert|3.2|L|cuin|0|abbr=on}}.<ref>[https://web.archive.org/web/20111005110138/http://www.pajero.com/gene/en/specifications/pdf/pajero_gene_spec.pdf Pajero/Montero Specifications] (PDF)</ref><ref>{{cite web |url=http://www.mitsubishi-motors.de/TechnicalSpecification.aspx?PMID=100&BTID=2674&VID1=5138&VID2=0&LangType=1031 |title=MITSUBISHI MOTORS in Deutschland |website=Mitsubishi-motors.de |date=2016-08-16 |access-date=2017-05-23 |url-status=dead |archive-url=https://web.archive.org/web/20130606081539/http://www.mitsubishi-motors.de/TechnicalSpecification.aspx?PMID=100&BTID=2674&VID1=5138&VID2=0&LangType=1031 |archive-date=2013-06-06 }}</ref>

Significant straight-four car engines include:

* 1954–1994 [[Alfa Romeo Twin Cam engine]]: one of the first mass-produced twin-cam engines.<ref name="bussoobit">{{cite web|url=http://www.italiaspeed.com/2006/cars/alfa_romeo/01/busso/2601.html|title=GIUSEPPE BUSSO, 1913-2006: A TRIBUTE TO ALFA ROMEO AND FERRARI'S GREAT ENGINEER|work=www.italiaspeed.com}}</ref> In 1990, it became the first production engine with [[variable valve timing]].<ref name="autobytel">{{cite web|url=http://www.autobytel.com/car-ownership/variable-valve-timing-vvt-104258/|title=Variable Valve Timing (VVT)|work=www.autobytel.com}}</ref>
* 1908–1941 [[Ford Model T engine]]: one of the most widely produced engines in the world.
* 1951–2000 [[BMC A-Series engine]]: the first engine to be used in a mass-production transverse-engined front-wheel drive car.
* 1966–2000 [[Fiat Twin Cam engine]]: one of the first mass-produced twin-cam engines, produced from 1959.
* 1968–1981 [[Triumph Slant-4 engine]]: an early [[multi-valve]] engine which formed the basis of Saab's first turbocharged engines.
* 2000–2009 [[Honda F20C engine]]: produced the highest specific output for a [[naturally aspirated engine]] of its time.

== Usage in racing cars ==
[[File:BMW F1 Engine M12 M13.JPG|thumb|right |1980s [[BMW M12|BMW M12/13]] Formula One engine]]

Many early racing cars used straight-four engines, however the Peugeot engine which won the [[1913 Indianapolis 500]] was a highly influential engine. Designed by [[Ernest Henry (engineer)|Ernest Henry]], this engine had [[Overhead_camshaft_engine#Double_overhead_camshaft|double overhead camshafts]] (DOHC) with four valves per cylinder, a layout that would become the standard until today for racing inline-four engines.<ref name=Ludvigsen>{{cite book|last=Ludvigsen|first=Karl|author-link=Karl Ludvigsen|title=Classic Racing Engines|publisher=Haynes Publishing| year=2001|isbn=1-85960-649-0}}</ref>{{refpage|pp. 14–17}}

Amongst the engines inspired by the Peugeot design was the [[Harry Arminius Miller|Miller engine]], which was a successful racing engine through the 1920s and early 1930s. The Miller engine evolved into the [[Offenhauser|Offenhauser engine]] which had a highly successful spanning from 1933 until 1981, including five straight victories at the Indianapolis 500 from 1971 to 1976.<ref name=Ludvigsen/>{{refpage|pp. 182–185}}

Many cars produced for the pre-WWII [[Voiturette (F2)|voiturette]] [[Grand Prix motor racing]] category used inline-four engine designs. 1.5&nbsp;L [[supercharger|supercharged]] engines found their way into cars such as the [[Maserati 4CL]] and various [[English Racing Automobiles]] (ERA) models. These were resurrected after the war, and formed the foundation of what was later to become [[Formula One]], although the straight-eight supercharged Alfettas would dominate the early years of F1.

Another engine that played an important role in racing history is the straight-four [[Ferrari]] engine designed by [[Aurelio Lampredi]]. This engine was originally designed as a 2&nbsp;L [[Formula 2]] engine for the Ferrari 500, but evolved to 2.5&nbsp;L to compete in [[Formula One]] in the Ferrari 625.<ref name=Ludvigsen/>{{refpage|pp. 78–81, 86–89}} For [[sports car]] racing, capacity was increased up to 3.4&nbsp;L for the Ferrari 860 Monza.

The [[Coventry Climax]] straight-four engine was also a very successful racing engine, which began life as a 1.5&nbsp;litre Formula 2 engine. Enlarged to 2.0&nbsp;litres for Formula One in 1958, it evolved into the large 2,495&nbsp;cc FPF that won the Formula One championship in [[Cooper Car Company|Cooper]]'s chassis in 1959 and 1960.<ref name=Ludvigsen/>{{refpage|pp. 130–133}}

In Formula One, the 1980s were dominated by the 1,500&nbsp;cc turbocharged cars. The [[BMW M12|BMW M12/13]] engine was notable for the era for its high boost pressures and performance. The cast iron block was based on a standard road car block and powered the F1 cars of Brabham, Arrows and Benetton and won the world championship in 1983. The 1986 version of the engine was said to produce about {{convert|1300|hp|kW|round=50|abbr=on}} in qualifying trim, at 5.5 bar of turbo boost.<ref>{{cite web|url=http://www.gurneyflap.com/bmwturbof1engine.html |title=BMW Turbo F1 Engine |publisher=Gurneyflap.com |access-date=2010-09-13}}</ref>

== Usage in motorcycles ==
{{See also|Motorcycle engine}}
[[File:Honda CB750 Engine.jpg|thumb |1970 [[Honda CB750]] engine]]

Belgian arms manufacturer [[FN Herstal]], which had been making [[FN (motorcycle)|motorcycles]] since 1901, began producing the first motorcycles with inline-fours in 1905.<ref name=cleveland>{{cite web |url=http://www.motorcycleclassics.com/classic-american-motorcycles/cleveland-motorcycles-zmsz17mjzhur |last=Siegal |first=Margie |title=The Same, But Different: 1927 Cleveland 4-45 and 4-61 Motorcycles |magazine=[[Motorcycle Classics]] |access-date=2017-06-20 |date=May–June 2017}}</ref> The [[FN Four]] had its engine mounted upright with the crankshaft [[Longitudinal engine|longitudinal]]. Other manufacturers that used this layout included [[Pierce-Arrow|Pierce]], [[Henderson Motorcycle|Henderson]], [[Ace Motor Corporation|Ace]], [[Cleveland Motorcycle Manufacturing Company|Cleveland]], and [[Indian Four|Indian]] in the United States, [[Nimbus (motorcycle)|Nimbus]] in Denmark, Windhoff in Germany, and [[Wilkinson Sword#Motorcycle production|Wilkinson]] in the United Kingdom.<ref name="CW4runners">{{cite journal |last= Edwards|first= David|date=August 1997|title= Four-Runners |journal= [[Cycle World]]|volume= 36|issue= 8|pages= 42–43|location= Newport Beach, CA USA|publisher= Hachette Filipacchi Magazines|editor1-first= David|editor1-last= Edwards|issn= 0011-4286|access-date= 2013-09-21|url= https://books.google.com/books?id=QGMMRS3b0KQC|ref= CW4runners}}</ref>

The first across-the-frame 4-cylinder motorcycle was the 1939 racer [[Gilera#History|Gilera 500 Rondine]], it also had double-over-head camshafts, forced-inducting supercharger and was [[Radiator (engine cooling)|liquid-cooled]].<ref name=first>{{cite web |url=https://www.motorcycleclassics.com/classic-italian-motorcycles/classic-gilera-motorcycles/1939-gilera-500-rondine-zm0z18jfzhur |last=Hamish |first=Cooper |title=Radical Rondine: 1939 Gilera 500 Rondine |magazine=[[Motorcycle Classics]] |access-date=2018-04-13 |date=January–February 2018}}</ref> Modern inline-four motorcycle engines first became popular with [[Honda]]'s [[SOHC]] [[Honda CB750|CB750]] introduced in 1969, and others followed in the 1970s. Since then, the inline-four has become one of the most common engine configurations in street bikes. Outside of the [[cruiser (motorcycle)|cruiser]] category, the inline-four is the most common configuration because of its relatively high performance-to-cost ratio.{{Citation needed|date=September 2013}} All major Japanese motorcycle manufacturers offer motorcycles with inline-four engines, as do [[MV Agusta]] and [[BMW motorcycles|BMW]]. BMW's earlier inline-four motorcycles were mounted horizontally along the frame, but all current four-cylinder BMW motorcycles have [[transverse engine]]s. The modern [[Triumph Motorcycles Ltd|Triumph]] company has offered inline-four-powered motorcycles, though they were discontinued in favour of [[Triumph Triple|triples]].

The 2009 [[Yamaha R1]] has an inline-four engine that does not fire at even intervals of 180°. Instead, it uses a [[crossplane]] crankshaft that prevents the pistons from simultaneously reaching top dead centre. This results in better [[secondary balance]], which is particularly beneficial in the higher rpm range, and "[[big-bang firing order]]" theory says the irregular delivery of torque to the rear tire makes sliding in the corners at racing speeds easier to control.

Inline-four engines are also used in [[Grand Prix motorcycle racing|MotoGP]] by the [[Suzuki MotoGP|Suzuki]] (since [[2015 MotoGP season|2015]]) and [[Yamaha Motor Racing|Yamaha]] (since [[2002 Grand Prix motorcycle racing season|2002]]) teams. In [[2010 Grand Prix motorcycle racing season|2010]], when the four-stroke Moto2 class was introduced, the engines for the class were a {{cvt|600|cc|cuin|1}} inline-four engine made by [[Honda Racing Corporation|Honda]] based on the [[Honda CBR600RR|CBR600RR]] with a maximum power output of {{cvt|110|kW|hp|round=5}}. Starting in [[2019 Moto2 season|2019]], the engines were replaced by a [[Triumph Motorcycles Ltd|Triumph]] {{cvt|765|cc|cuin|1}} [[straight-three engine|triple engine]].

== Usage in light and medium duty commercial vehicles ==

Inline-four engines are also used in light duty commercial vehicles such as [[Karsan Jest]] and [[Mercedes-Benz Sprinter]].

== See also ==
* [[Flat-four engine]]
* [[V4 engine]]

==References==
{{Reflist|30em}}

== External links ==
* {{commons category inline|Straight-4 engines}}

{{Piston engine configurations}}

{{DEFAULTSORT:Straight-Four Engine}}
[[Category:Straight-four engines| ]]
[[Category:Straight engines|4]]