Editing Flat-four engine (section)

== Use in automobiles ==
=== 1900–1935 ===
[[File:Wilson-Pilcher flat-4 engine.jpg|thumb|1904 [[Wilson-Pilcher]] water-cooled engine]]
In 1900, the first flat-four engine was produced by [[Karl Benz#Benz & Cie. and the Benz Patent Motorwagen|Benz & Cie]], based on Benz's  1897 "contra" flat-twin engine.{{citation needed|date=September 2019}} This engine was used in Benz racing cars, produced {{convert|20|hp|kW|0|abbr=on}}, had a displacement of {{convert|5.4|L|cuin|0|abbr=on}} and was designed by Georg Diehl.

London company [[Wilson-Pilcher]] released its first car in 1901, which was powered by a flat-four engine. This engine was mounted longitudinally in the chassis, water-cooled, produced {{convert|9|hp|kW|0|abbr=on}} and had a displacement of {{convert|2.4|L|cuin|0|abbr=on}}. Unusually for its day, the bore and stroke were equal, with each being {{convert|95|mm|in|1|abbr=on}}.

In 1902 the Buffum automobile was equipped with opposed four cylinder engines that were rated at 16 horsepower. Herbert H. Buffum produced an American Automobile called the Buffum in Abington, Massachusetts from 1903 to 1907.<ref>{{cite web |title=The Buffum Automobile |url=http://www.american-automobiles.com/Buffum.html |publisher=Farber and Associates |access-date=2019-10-27 |archive-date=2019-04-23 |archive-url=https://web.archive.org/web/20190423025054/http://www.american-automobiles.com/Buffum.html |url-status=dead }}</ref>

Having previously produced flat-twin engines, the 1926 [[Tatra 30]] was the Czech company's first model powered by a flat-four engine. Tatra produced various flat-four engined model through the 1920s and 1930s.
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=== 1936–1999 ===
{{More citations needed section|date=December 2023}}
{{multiple image
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| image1            = Flat Four Jowett Engine from a Jowett Jupiter.jpg
| caption1          = 1952 [[Jowett Jupiter]] water-cooled engine
| image2            = 1955 Porsche 550 Spyder engine.jpg
| caption2          = 1955 [[Porsche 550 Spyder]] air-cooled engine
}}

The 1936 [[Tatra T97]] pioneered the rear-engined, air-cooled flat-four, backbone chassis layout (later used by the [[Volkswagen Beetle]]), and at the same time, though unrelated, came the [[Steyr 50]] from Austria, sporting a front boxer 4 engine with rear wheel drive. Also in 1936, English company [[Jowett Cars|Jowett]] expanded its model range from flat-twin engines to also include flat-four engines. Production of Jowett flat-four engines continued until 1954, when the [[Jowett Javelin]] saloon and [[Jowett Jupiter]] sports models ended production.

The longest production flat-four engine is the [[Volkswagen air-cooled engine]], which was produced from 1938 until 2006 and was most famously used in the rear-engined 1938–2003 [[Volkswagen Beetle]] and 1950–1983 [[Volkswagen Transporter]].<ref>{{cite news |title=The engine that Benz built still survives |url=https://www.theglobeandmail.com/globe-drive/reviews/classics/the-engine-that-benz-built-still-survives/article4317376/ |newspaper=The Globe and Mail |date=29 April 2010 |access-date=1 September 2019}}</ref> This air-cooled engine was designed by Porsche and was also used in the 1948–1965 [[Porsche 356]], 1953–1956 [[Porsche 550]], 1965–1969 [[Porsche 912]] and 1969–1976 [[Porsche 914]]. In 1984, to comply with exhaust emissions regulations a water-cooled version called the [[Volkswagen Wasserboxer engine]] was introduced in the [[Volkswagen Type 2 (T3)|Volkswagen Transporter (T3)]]

During the 1960s and 1970s, several manufacturers produced flat-four engines including the air-cooled [[Citroën GS#Mechanics|Citroën flat-four engine]], the water-cooled [[Alfa Romeo Flat-4 engine|Alfa Romeo flat-four engine]], the water-cooled [[Lancia Flat-4 engine|Lancia flat-four engine]] and the water-cooled [[Subaru EA engine]].

Two important engines designed during this period, but never saw the light of day in series production, were the Morris 800cc side valve engine by Alec Issigonis in 1947 originally destined for the Morris Minor, and the Ferguson 2.2 litre SOHC engine by Claude Hill in 1966 as part of the R5 vehicle research project.

=== 2000–present===
[[File:Subaru BRZ engine (20413082204).jpg|thumb |2012–present [[Subaru FA engine|Subaru FA]] water-cooled engine]]

By 2000, most manufacturers had replaced flat-four engines with inline-four engines. A notable exception is Subaru, with the water-cooled [[Subaru EJ engine]] being available in turbocharged form in the [[Subaru WRX]] sports sedan and its [[World Rally Car]] counterpart. Subaru's adoption of [[all-wheel drive]] was a factor in retaining the flat-four engine, since the shorter length of this engine assists in fitting the all-wheel drive components into the chassis.<ref name=popsci>{{cite journal |last=Stepler |first=Richard |title=Preview Drive: Three Ways to Get a Grip |journal=Popular Science |date=September 1994 |volume=245 |issue=3 |page=44 |url=https://books.google.com/books?id=RudyJP1ByycC&pg=PA44 |access-date=2011-10-23}}</ref>  Although it is more expensive than an inline-four engine, the flat-four engine allows Subaru to build an all-wheel drive vehicle at little extra cost from two-wheel drive.<ref name=popsci/>

In 2012, a naturally aspirated version of the [[Subaru FA engine]] was used in the [[Toyota 86]] (also called the "Subaru BRZ" and "Scion FR-S") rear-wheel drive sports coupe.<ref name=Bonk>{{cite web |last=Bonk |first=Aaron (2013-02-07) |title=How Boxer Engines Work, And Why You Should Care About Subaru's New FA20 |url=http://www.superstreetonline.com/techarticles/sstp_1301_how_boxer_engines_work/ |access-date=8 January 2014 |date=2013-02-07 |archive-date=2014-02-27 |archive-url=https://web.archive.org/web/20140227052947/http://www.superstreetonline.com/techarticles/sstp_1301_how_boxer_engines_work/ |url-status=dead }}</ref> This engine is water-cooled, has [[gasoline direct injection]], produces {{convert|147|kW|hp|0|abbr=on}} and has a displacement of {{convert|2.0|L|cuin|0|abbr=on}}.

The 2016 [[Porsche 982|Porsche Boxster/Cayman (982)]] mid-engined sports cars downsized from a naturally aspirated flat-six engine to a turbocharged flat-four engine, Porsche's first flat-four since the mid-1970s. This engine is produced in displacements of {{convert|2.0|-|2.5|L|cuin|0|abbr=on}} and produces up to {{convert|365|hp|kW|0|abbr=on}}.<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> Several reviewers criticised the Boxster/Cayman for an uninspiring engine sound.<ref>{{cite web |title=2019 Porsche 718 Cayman |url=https://www.caranddriver.com/porsche/718-cayman |website=www.caranddriver.com |access-date=1 September 2019 |date=14 May 2019}}</ref><ref>{{cite web |title=Porsche 718 Cayman review – The entry-level Porsche punches above its weight |url=https://www.evo.co.uk/porsche/718-cayman |website=www.evo.co.uk |access-date=1 September 2019 |language=en}}</ref><ref>{{cite web |title=2017 Porsche 718 Cayman First Drive Review: Performance Trumps Sound |url=https://www.motortrend.com/cars/porsche/718-cayman/2017/2017-porsche-718-cayman-first-drive-review/ |website=www.motortrend.com |access-date=1 September 2019}}</ref>

In 2025, Chinese automaker BYD introduced its first flat-four engine in the BYD U7 luxury sedan, marking a modern revival of the boxer engine layout. This water-cooled, turbocharged powerplant combined direct injection and hybrid technology, delivering 268 hp (200 kW) while maintaining a compact design ideal for the sedan’s all-wheel-drive system. The engine drew inspiration from Porsche’s turbocharged flat-four units and showcased BYD’s push into high-performance powertrains alongside its electric vehicle lineup.<ref>{{Cite web |last=White |first=Tom |date=28 March 2025 |title=BYD's new engine shock! New Subaru-style turbo boxer engine headlines unique performance hybrid YangWang U7 sedan as the Chinese brand takes aim at the Porsche Panamera, BMW i7, and Audi e-tron GT |url=https://www.carsguide.com.au/car-news/byds-new-engine-shock-new-subaru-style-turbo-boxer-engine-headlines-unique-performance |url-status=live}}</ref><ref>{{Cite web |last=Lewis |first=William Irvin |date=2025-04-06 |title=Chinese EV Maker Creates 268 HP Turbo Boxer Engine |url=https://www.hotcars.com/byd-creates-boxer-engine/ |access-date=2025-05-10 |website=HotCars |language=en}}</ref>