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class="vector-toc-numb">2.3</span> <span>2000–present</span> </div> </a> <ul id="toc-2000–present-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Use_in_motorcycles" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Use_in_motorcycles"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>Use in motorcycles</span> </div> </a> <ul id="toc-Use_in_motorcycles-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Use_in_aircraft" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Use_in_aircraft"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Use in aircraft</span> </div> </a> <ul id="toc-Use_in_aircraft-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" title="Table of Contents" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" 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href="https://ar.wikipedia.org/wiki/%D9%85%D8%AD%D8%B1%D9%83_%D9%85%D8%B3%D8%B7%D8%AD_%D8%B1%D8%A8%D8%A7%D8%B9%D9%8A" title="محرك مسطح رباعي – Arabic" lang="ar" hreflang="ar" data-title="محرك مسطح رباعي" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/Boksermotor-4" title="Boksermotor-4 – Danish" lang="da" hreflang="da" data-title="Boksermotor-4" data-language-autonym="Dansk" data-language-local-name="Danish" class="interlanguage-link-target"><span>Dansk</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Moteur_avec_quatre_cylindres_%C3%A0_plat" title="Moteur avec quatre cylindres à plat – French" lang="fr" hreflang="fr" data-title="Moteur avec quatre cylindres à plat" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/4%EA%B8%B0%ED%86%B5_%EC%88%98%ED%8F%89_%EC%97%94%EC%A7%84" title="4기통 수평 엔진 – Korean" lang="ko" hreflang="ko" data-title="4기통 수평 엔진" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Mesin_4_silinder_mendatar" title="Mesin 4 silinder mendatar – Indonesian" lang="id" hreflang="id" data-title="Mesin 4 silinder mendatar" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target"><span>Bahasa Indonesia</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Motore_a_quattro_cilindri_contrapposti" title="Motore a quattro cilindri contrapposti – Italian" lang="it" hreflang="it" data-title="Motore a quattro cilindri contrapposti" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E6%B0%B4%E5%B9%B3%E5%AF%BE%E5%90%914%E6%B0%97%E7%AD%92" title="水平対向4気筒 – Japanese" lang="ja" hreflang="ja" data-title="水平対向4気筒" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/B4_(silnik)" title="B4 (silnik) – Polish" lang="pl" hreflang="pl" data-title="B4 (silnik)" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target"><span>Polski</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Motor_boxer_de_quatro_cilindros" title="Motor boxer de quatro cilindros – Portuguese" lang="pt" hreflang="pt" data-title="Motor boxer de quatro cilindros" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-sk mw-list-item"><a href="https://sk.wikipedia.org/wiki/B4_(motor)" title="B4 (motor) – Slovak" lang="sk" hreflang="sk" data-title="B4 (motor)" data-language-autonym="Slovenčina" data-language-local-name="Slovak" class="interlanguage-link-target"><span>Slovenčina</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/%E6%B0%B4%E5%B9%B3%E5%B0%8D%E8%87%A5%E5%9B%9B%E7%BC%B8%E5%BC%95%E6%93%8E" title="水平對臥四缸引擎 – Chinese" lang="zh" hreflang="zh" data-title="水平對臥四缸引擎" data-language-autonym="中文" data-language-local-name="Chinese" class="interlanguage-link-target"><span>中文</span></a></li> </ul> <div class="after-portlet after-portlet-lang"><span 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searchaux" style="display:none">Horizontally opposed four-cylinder piston engine</div> <style data-mw-deduplicate="TemplateStyles:r1251242444">.mw-parser-output .ambox{border:1px solid #a2a9b1;border-left:10px solid #36c;background-color:#fbfbfb;box-sizing:border-box}.mw-parser-output .ambox+link+.ambox,.mw-parser-output .ambox+link+style+.ambox,.mw-parser-output .ambox+link+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+style+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+link+.ambox{margin-top:-1px}html body.mediawiki .mw-parser-output .ambox.mbox-small-left{margin:4px 1em 4px 0;overflow:hidden;width:238px;border-collapse:collapse;font-size:88%;line-height:1.25em}.mw-parser-output .ambox-speedy{border-left:10px solid #b32424;background-color:#fee7e6}.mw-parser-output .ambox-delete{border-left:10px solid #b32424}.mw-parser-output .ambox-content{border-left:10px solid #f28500}.mw-parser-output .ambox-style{border-left:10px solid #fc3}.mw-parser-output .ambox-move{border-left:10px solid #9932cc}.mw-parser-output .ambox-protection{border-left:10px solid #a2a9b1}.mw-parser-output .ambox .mbox-text{border:none;padding:0.25em 0.5em;width:100%}.mw-parser-output .ambox .mbox-image{border:none;padding:2px 0 2px 0.5em;text-align:center}.mw-parser-output .ambox .mbox-imageright{border:none;padding:2px 0.5em 2px 0;text-align:center}.mw-parser-output .ambox .mbox-empty-cell{border:none;padding:0;width:1px}.mw-parser-output .ambox .mbox-image-div{width:52px}@media(min-width:720px){.mw-parser-output .ambox{margin:0 10%}}@media print{body.ns-0 .mw-parser-output .ambox{display:none!important}}</style><table class="box-Original_research plainlinks metadata ambox ambox-content ambox-Original_research" role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><span typeof="mw:File"><span><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/b/b4/Ambox_important.svg/40px-Ambox_important.svg.png" decoding="async" width="40" height="40" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/b/b4/Ambox_important.svg/60px-Ambox_important.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/b/b4/Ambox_important.svg/80px-Ambox_important.svg.png 2x" data-file-width="40" data-file-height="40" /></span></span></div></td><td class="mbox-text"><div class="mbox-text-span">This article <b>possibly contains <a href="/wiki/Wikipedia:No_original_research" title="Wikipedia:No original research">original research</a></b>.<span class="hide-when-compact"> Please <a class="external text" href="https://en.wikipedia.org/w/index.php?title=Flat-four_engine&action=edit">improve it</a> by <a href="/wiki/Wikipedia:Verifiability" title="Wikipedia:Verifiability">verifying</a> the claims made and adding <a href="/wiki/Wikipedia:Citing_sources#Inline_citations" title="Wikipedia:Citing sources">inline citations</a>. Statements consisting only of original research should be removed.</span> <span class="date-container"><i>(<span class="date">December 2023</span>)</i></span><span class="hide-when-compact"><i> (<small><a href="/wiki/Help:Maintenance_template_removal" title="Help:Maintenance template removal">Learn how and when to remove this message</a></small>)</i></span></div></td></tr></tbody></table> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:UL350iS_ULPower_aircraft_engine.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/2/2e/UL350iS_ULPower_aircraft_engine.jpg/220px-UL350iS_ULPower_aircraft_engine.jpg" decoding="async" width="220" height="147" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/2e/UL350iS_ULPower_aircraft_engine.jpg/330px-UL350iS_ULPower_aircraft_engine.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/2e/UL350iS_ULPower_aircraft_engine.jpg/440px-UL350iS_ULPower_aircraft_engine.jpg 2x" data-file-width="3000" data-file-height="2000" /></a><figcaption>ULPower UL360iS aircraft piston engine</figcaption></figure> <p>A <b>flat-four engine</b>, also known as a <b>horizontally opposed-four engine</b> or <b>boxer engine</b>,<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> is a four-cylinder <a href="/wiki/Piston_engine" class="mw-redirect" title="Piston engine">piston engine</a> with two banks of cylinders lying on opposite sides of a common crankshaft. The most common type of flat-four engine is the <b>boxer-four engine</b>, each pair of opposed pistons moves inwards and outwards at the same time. </p><p>A boxer-four engine has perfect primary and secondary balance, however, the two cylinder heads means the design is more expensive to produce than a <a href="/wiki/Straight-four_engine" title="Straight-four engine">straight-four engine</a>. There is a minor, secondary unbalanced rotational torque pulse in the plane of the pistons, when a piston pair at one end of the engine is at TDC and the other pair at BDC. The TDC pair creates a torque greater than the BDC pair, so the net unbalanced torque pulse is the difference. The difference in TDC vs BDC inertial forces is explained in the <b>Engine balance</b> section. Boxer-four engines have been used in cars since 1897, especially by Volkswagen and Subaru. They have also occasionally been used in motorcycles and frequently in aircraft. <a href="/wiki/Cessna" title="Cessna">Cessna</a> and <a href="/wiki/Piper_Aircraft" title="Piper Aircraft">Piper</a> use flat four engines from <a href="/wiki/Lycoming_Engines" title="Lycoming Engines">Lycoming</a> and <a href="/wiki/Continental_Aerospace_Technologies" title="Continental Aerospace Technologies">Continental</a> in the most <a href="/wiki/List_of_most-produced_aircraft" title="List of most-produced aircraft">common civil aircraft</a> in the world - the <a href="/wiki/Cessna_172" title="Cessna 172">Cessna 172</a>, and <a href="/wiki/Piper_Cherokee" class="mw-redirect" title="Piper Cherokee">Piper Cherokee</a>, while many <a href="/wiki/Ultralight_aviation" title="Ultralight aviation">ultralight</a> and <a href="/wiki/Light-sport_aircraft" title="Light-sport aircraft">LSA</a> planes use versions of the <a href="/wiki/Rotax_912" title="Rotax 912">Rotax 912</a>. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Design">Design</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Flat-four_engine&action=edit&section=1" title="Edit section: Design"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Vierzylinder_Boxermotor.gif" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/a/a8/Vierzylinder_Boxermotor.gif/220px-Vierzylinder_Boxermotor.gif" decoding="async" width="220" height="185" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/a8/Vierzylinder_Boxermotor.gif/330px-Vierzylinder_Boxermotor.gif 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/a8/Vierzylinder_Boxermotor.gif/440px-Vierzylinder_Boxermotor.gif 2x" data-file-width="576" data-file-height="485" /></a><figcaption>Boxer-four animation</figcaption></figure> <p>In a flat-four engine, each pair of opposing <a href="/wiki/Piston" title="Piston">pistons</a> successively moves inwards together and outwards together. The advantages of the boxer-four layout are perfect secondary vibration (resulting in minimal vibration), a low <a href="/wiki/Centre_of_gravity" class="mw-redirect" title="Centre of gravity">centre of gravity</a>, and a short engine length. Flat-four engine have successfully used <a href="/wiki/Air_cooling" title="Air cooling">air cooling</a>, although air-cooled engines are noisier and have a lower power output than an equivalent engine with <a href="/wiki/Liquid_cooling" title="Liquid cooling">liquid cooling</a>. In light aircraft, where lightness is of primary importance, air-cooling has traditionally been common.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> </p><p>The downsides of boxer-four engines (compared with inline-four engines) are their extra width, the increased costs associated with having two cylinder heads instead of one, and the long exhaust manifold required to achieve evenly spaced exhaust pulses.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> Due to these factors, <a href="/wiki/Straight-four_engine" title="Straight-four engine">straight-four engines</a> are more common in cars than are flat-four engines, and <a href="/wiki/V6_engine" title="V6 engine">V6 engines</a> are often used where larger displacements are required.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Engine_balance">Engine balance</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Flat-four_engine&action=edit&section=2" title="Edit section: Engine balance"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The equal and opposing forces generated in a boxer-four engine result in perfect <a href="/wiki/Secondary_balance" class="mw-redirect" title="Secondary balance">secondary balance</a> (unlike the unbalanced vertical forces produced by inline-four engines). Boxer-four engines are therefore better suited to displacements above 2.0 L (122 cu in), since they do not require <a href="/wiki/Balance_shaft" title="Balance shaft">balance shafts</a> to reduce the secondary vibration. </p><p>In a boxer engine, each cylinder is slightly offset from its opposing pair due to the distance between the <a href="/wiki/Crankpin" title="Crankpin">crankpin</a> journals. This offset gives rise to a slight <a href="/wiki/Couple_(mechanics)" title="Couple (mechanics)">rocking couple</a>,<sup id="cite_ref-Wilson_5-0" class="reference"><a href="#cite_note-Wilson-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page: 27">: 27 </span></sup> but any resulting vibration is normally insufficient to require balance shafts. </p><p>As with all four-stroke engines of four cylinders or fewer, the lack of overlap in the <a href="/wiki/Power_stroke_(engine)" class="mw-redirect" title="Power stroke (engine)">power strokes</a> results in a pulsating delivery of torque to the <a href="/wiki/Flywheel" title="Flywheel">flywheel</a>, causing a torsional vibration along the crankshaft axis.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> Such vibration, if excessive, may be minimised using a <a href="/wiki/Harmonic_damper" title="Harmonic damper">harmonic damper</a>. </p> <div class="mw-heading mw-heading3"><h3 id="Exhaust_manifold">Exhaust manifold</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Flat-four_engine&action=edit&section=3" title="Edit section: Exhaust manifold"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The typical firing order for a boxer-four engine is for the left bank of cylinders to ignite one after another, followed by the right bank of cylinders (or vice versa), with the <a href="/wiki/Firing_order#Even_and_uneven_firing_order" title="Firing order">firing interval</a> evenly spaced at 180 degrees. Traditionally, the exhausts from the two cylinders on each bank were merged, with the resulting uneven exhaust pulses causing a characteristic "flat-four burble" exhaust sound. </p><p>The other common exhaust configuration (such as used by Subaru since the mid-2000s) is to pair the cylinders with a firing interval offset of 360 degrees, in order to optimise the <a href="/wiki/Exhaust_manifold#Exhaust_scavenging" title="Exhaust manifold">exhaust pulses</a>.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> This configuration requires long exhaust manifolds, in order to pair the cylinders on opposite banks, and results in a less distinctive exhaust sound. </p> <div class="mw-heading mw-heading2"><h2 id="Use_in_automobiles">Use in automobiles</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Flat-four_engine&action=edit&section=4" title="Edit section: Use in automobiles"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading3"><h3 id="1900–1935"><span id="1900.E2.80.931935"></span>1900–1935</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Flat-four_engine&action=edit&section=5" title="Edit section: 1900–1935"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Wilson-Pilcher_flat-4_engine.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/9/98/Wilson-Pilcher_flat-4_engine.jpg/220px-Wilson-Pilcher_flat-4_engine.jpg" decoding="async" width="220" height="183" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/98/Wilson-Pilcher_flat-4_engine.jpg/330px-Wilson-Pilcher_flat-4_engine.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/98/Wilson-Pilcher_flat-4_engine.jpg/440px-Wilson-Pilcher_flat-4_engine.jpg 2x" data-file-width="717" data-file-height="595" /></a><figcaption>1904 <a href="/wiki/Wilson-Pilcher" title="Wilson-Pilcher">Wilson-Pilcher</a> water-cooled engine</figcaption></figure> <p>In 1900, the first flat-four engine was produced by <a href="/wiki/Karl_Benz#Benz_&_Cie._and_the_Benz_Patent_Motorwagen" class="mw-redirect" title="Karl Benz">Benz & Cie</a>, based on Benz's 1897 "contra" flat-twin engine.<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (September 2019)">citation needed</span></a></i>]</sup> This engine was used in Benz racing cars, produced 20 hp (15 kW), had a displacement of 5.4 L (330 cu in) and was designed by Georg Diehl. </p><p>London company <a href="/wiki/Wilson-Pilcher" title="Wilson-Pilcher">Wilson-Pilcher</a> 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 9 hp (7 kW) and had a displacement of 2.4 L (146 cu in). Unusually for its day, the bore and stroke were equal, with each being 95 mm (3.7 in). </p><p>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.<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> </p><p>Having previously produced flat-twin engines, the 1926 <a href="/wiki/Tatra_30" title="Tatra 30">Tatra 30</a> 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. </p> <div style="clear:right;" class=""></div> <div class="mw-heading mw-heading3"><h3 id="1936–1999"><span id="1936.E2.80.931999"></span>1936–1999</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Flat-four_engine&action=edit&section=6" title="Edit section: 1936–1999"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1251242444"><table class="box-More_citations_needed_section plainlinks metadata ambox ambox-content ambox-Refimprove" role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><span typeof="mw:File"><a href="/wiki/File:Question_book-new.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png" decoding="async" width="50" height="39" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/75px-Question_book-new.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/100px-Question_book-new.svg.png 2x" data-file-width="512" data-file-height="399" /></a></span></div></td><td class="mbox-text"><div class="mbox-text-span">This section <b>needs additional citations for <a href="/wiki/Wikipedia:Verifiability" title="Wikipedia:Verifiability">verification</a></b>.<span class="hide-when-compact"> Please help <a href="/wiki/Special:EditPage/Flat-four_engine" title="Special:EditPage/Flat-four engine">improve this article</a> by <a href="/wiki/Help:Referencing_for_beginners" title="Help:Referencing for beginners">adding citations to reliable sources</a> in this section. Unsourced material may be challenged and removed.</span> <span class="date-container"><i>(<span class="date">December 2023</span>)</i></span><span class="hide-when-compact"><i> (<small><a href="/wiki/Help:Maintenance_template_removal" title="Help:Maintenance template removal">Learn how and when to remove this message</a></small>)</i></span></div></td></tr></tbody></table> <style data-mw-deduplicate="TemplateStyles:r1273380762/mw-parser-output/.tmulti">.mw-parser-output .tmulti .multiimageinner{display:flex;flex-direction:column}.mw-parser-output .tmulti .trow{display:flex;flex-direction:row;clear:left;flex-wrap:wrap;width:100%;box-sizing:border-box}.mw-parser-output .tmulti .tsingle{margin:1px;float:left}.mw-parser-output .tmulti .theader{clear:both;font-weight:bold;text-align:center;align-self:center;background-color:transparent;width:100%}.mw-parser-output .tmulti .thumbcaption{background-color:transparent}.mw-parser-output .tmulti .text-align-left{text-align:left}.mw-parser-output .tmulti .text-align-right{text-align:right}.mw-parser-output .tmulti .text-align-center{text-align:center}@media all and (max-width:720px){.mw-parser-output .tmulti .thumbinner{width:100%!important;box-sizing:border-box;max-width:none!important;align-items:center}.mw-parser-output .tmulti .trow{justify-content:center}.mw-parser-output .tmulti .tsingle{float:none!important;max-width:100%!important;box-sizing:border-box;text-align:center}.mw-parser-output .tmulti .tsingle .thumbcaption{text-align:left}.mw-parser-output .tmulti .trow>.thumbcaption{text-align:center}}@media screen{html.skin-theme-clientpref-night .mw-parser-output .tmulti .multiimageinner span:not(.skin-invert-image):not(.skin-invert):not(.bg-transparent) img{background-color:white}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .tmulti .multiimageinner span:not(.skin-invert-image):not(.skin-invert):not(.bg-transparent) img{background-color:white}}</style><div class="thumb tmulti tright"><div class="thumbinner multiimageinner" style="width:224px;max-width:224px"><div class="trow"><div class="tsingle" style="width:222px;max-width:222px"><div class="thumbimage"><span typeof="mw:File"><a href="/wiki/File:Flat_Four_Jowett_Engine_from_a_Jowett_Jupiter.jpg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e0/Flat_Four_Jowett_Engine_from_a_Jowett_Jupiter.jpg/220px-Flat_Four_Jowett_Engine_from_a_Jowett_Jupiter.jpg" decoding="async" width="220" height="172" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/e0/Flat_Four_Jowett_Engine_from_a_Jowett_Jupiter.jpg/330px-Flat_Four_Jowett_Engine_from_a_Jowett_Jupiter.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/e0/Flat_Four_Jowett_Engine_from_a_Jowett_Jupiter.jpg/440px-Flat_Four_Jowett_Engine_from_a_Jowett_Jupiter.jpg 2x" data-file-width="3882" data-file-height="3036" /></a></span></div><div class="thumbcaption">1952 <a href="/wiki/Jowett_Jupiter" title="Jowett Jupiter">Jowett Jupiter</a> water-cooled engine</div></div></div><div class="trow"><div class="tsingle" style="width:222px;max-width:222px"><div class="thumbimage"><span typeof="mw:File"><a href="/wiki/File:1955_Porsche_550_Spyder_engine.jpg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/1/12/1955_Porsche_550_Spyder_engine.jpg/220px-1955_Porsche_550_Spyder_engine.jpg" decoding="async" width="220" height="146" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/12/1955_Porsche_550_Spyder_engine.jpg/330px-1955_Porsche_550_Spyder_engine.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/12/1955_Porsche_550_Spyder_engine.jpg/440px-1955_Porsche_550_Spyder_engine.jpg 2x" data-file-width="2142" data-file-height="1417" /></a></span></div><div class="thumbcaption">1955 <a href="/wiki/Porsche_550_Spyder" class="mw-redirect" title="Porsche 550 Spyder">Porsche 550 Spyder</a> air-cooled engine</div></div></div></div></div> <p>The 1936 <a href="/wiki/Tatra_T97" class="mw-redirect" title="Tatra T97">Tatra T97</a> pioneered the rear-engined, air-cooled flat-four, backbone chassis layout (later used by the <a href="/wiki/Volkswagen_Beetle" title="Volkswagen Beetle">Volkswagen Beetle</a>), and at the same time, though unrelated, came the <a href="/wiki/Steyr_50" title="Steyr 50">Steyr 50</a> from Austria, sporting a front boxer 4 engine with rear wheel drive. Also in 1936, English company <a href="/wiki/Jowett_Cars" title="Jowett Cars">Jowett</a> 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 <a href="/wiki/Jowett_Javelin" title="Jowett Javelin">Jowett Javelin</a> saloon and <a href="/wiki/Jowett_Jupiter" title="Jowett Jupiter">Jowett Jupiter</a> sports models ended production. </p><p>The longest production flat-four engine is the <a href="/wiki/Volkswagen_air-cooled_engine" title="Volkswagen air-cooled engine">Volkswagen air-cooled engine</a>, which was produced from 1938 until 2006 and was most famously used in the rear-engined 1938–2003 <a href="/wiki/Volkswagen_Beetle" title="Volkswagen Beetle">Volkswagen Beetle</a> and 1950–1983 <a href="/wiki/Volkswagen_Transporter" title="Volkswagen Transporter">Volkswagen Transporter</a>.<sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> This air-cooled engine was designed by Porsche and was also used in the 1948–1965 <a href="/wiki/Porsche_356" title="Porsche 356">Porsche 356</a>, 1953–1956 <a href="/wiki/Porsche_550" title="Porsche 550">Porsche 550</a>, 1965–1969 <a href="/wiki/Porsche_912" title="Porsche 912">Porsche 912</a> and 1969–1976 <a href="/wiki/Porsche_914" title="Porsche 914">Porsche 914</a>. In 1984, to comply with exhaust emissions regulations a water-cooled version called the <a href="/wiki/Volkswagen_Wasserboxer_engine" title="Volkswagen Wasserboxer engine">Volkswagen Wasserboxer engine</a> was introduced in the <a href="/wiki/Volkswagen_Type_2_(T3)" title="Volkswagen Type 2 (T3)">Volkswagen Transporter (T3)</a> </p><p>During the 1960s and 1970s, several manufacturers produced flat-four engines including the air-cooled <a href="/wiki/Citro%C3%ABn_GS#Mechanics" title="Citroën GS">Citroën flat-four engine</a>, the water-cooled <a href="/wiki/Alfa_Romeo_Flat-4_engine" class="mw-redirect" title="Alfa Romeo Flat-4 engine">Alfa Romeo flat-four engine</a>, the water-cooled <a href="/wiki/Lancia_Flat-4_engine" title="Lancia Flat-4 engine">Lancia flat-four engine</a> and the water-cooled <a href="/wiki/Subaru_EA_engine" title="Subaru EA engine">Subaru EA engine</a>. </p><p>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. </p> <div class="mw-heading mw-heading3"><h3 id="2000–present"><span id="2000.E2.80.93present"></span>2000–present</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Flat-four_engine&action=edit&section=7" title="Edit section: 2000–present"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Subaru_BRZ_engine_(20413082204).jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/9/95/Subaru_BRZ_engine_%2820413082204%29.jpg/220px-Subaru_BRZ_engine_%2820413082204%29.jpg" decoding="async" width="220" height="165" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/95/Subaru_BRZ_engine_%2820413082204%29.jpg/330px-Subaru_BRZ_engine_%2820413082204%29.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/95/Subaru_BRZ_engine_%2820413082204%29.jpg/440px-Subaru_BRZ_engine_%2820413082204%29.jpg 2x" data-file-width="2592" data-file-height="1944" /></a><figcaption>2012–present <a href="/wiki/Subaru_FA_engine" title="Subaru FA engine">Subaru FA</a> water-cooled engine</figcaption></figure> <p>By 2000, most manufacturers had replaced flat-four engines with inline-four engines. A notable exception is Subaru, with the water-cooled <a href="/wiki/Subaru_EJ_engine" title="Subaru EJ engine">Subaru EJ engine</a> being available in turbocharged form in the <a href="/wiki/Subaru_WRX" title="Subaru WRX">Subaru WRX</a> sports sedan and its <a href="/wiki/World_Rally_Car" title="World Rally Car">World Rally Car</a> counterpart. Subaru's adoption of <a href="/wiki/All-wheel_drive" class="mw-redirect" title="All-wheel drive">all-wheel drive</a> 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.<sup id="cite_ref-popsci_12-0" class="reference"><a href="#cite_note-popsci-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> 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.<sup id="cite_ref-popsci_12-1" class="reference"><a href="#cite_note-popsci-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> </p><p>In 2012, a naturally aspirated version of the <a href="/wiki/Subaru_FA_engine" title="Subaru FA engine">Subaru FA engine</a> was used in the <a href="/wiki/Toyota_86" title="Toyota 86">Toyota 86</a> (also called the "Subaru BRZ" and "Scion FR-S") rear-wheel drive sports coupe.<sup id="cite_ref-Bonk_13-0" class="reference"><a href="#cite_note-Bonk-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> This engine is water-cooled, has <a href="/wiki/Gasoline_direct_injection" title="Gasoline direct injection">gasoline direct injection</a>, produces 147 kW (197 hp) and has a displacement of 2.0 L (122 cu in). </p><p>The 2016 <a href="/wiki/Porsche_982" class="mw-redirect" title="Porsche 982">Porsche Boxster/Cayman (982)</a> 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 2.0–2.5 L (122–153 cu in) and produces up to 365 hp (272 kW).<sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> Several reviewers criticised the Boxster/Cayman for an uninspiring engine sound.<sup id="cite_ref-15" class="reference"><a href="#cite_note-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-16" class="reference"><a href="#cite_note-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-17" class="reference"><a href="#cite_note-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Use_in_motorcycles">Use in motorcycles</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Flat-four_engine&action=edit&section=8" title="Edit section: Use in motorcycles"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Motorcycle_engine" title="Motorcycle engine">Motorcycle engine</a></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Glengine.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/d/df/Glengine.jpg/220px-Glengine.jpg" decoding="async" width="220" height="142" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/d/df/Glengine.jpg/330px-Glengine.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/d/df/Glengine.jpg/440px-Glengine.jpg 2x" data-file-width="600" data-file-height="386" /></a><figcaption><a href="/wiki/Honda_Gold_Wing" title="Honda Gold Wing">Honda GL1000</a> </figcaption></figure> <p>Most motorcycles with four-cylinder engines use a <a href="/wiki/Straight-four_engine" title="Straight-four engine">straight-four engine</a> layout, however, several flat-four engine engines have been used in <a href="/wiki/Drive_shaft#Motorcycle_drive_shafts" title="Drive shaft">shaft drive</a> motorcycles: </p> <ul><li>1938–1939 <a href="/wiki/Z%C3%BCndapp" title="Zündapp">Zündapp K800</a> (air-cooled)</li> <li>1974–1987 <a href="/wiki/Honda_Gold_Wing" title="Honda Gold Wing">Honda Gold Wing</a> (liquid-cooled)</li> <li>1955–1956 <a href="/wiki/Wooler_(motorcycles)#Post_WW2_motorcycles" title="Wooler (motorcycles)">Wooler 500cc</a> (air-cooled)</li> <li>1981–1982 <a href="/w/index.php?title=BFG_1300&action=edit&redlink=1" class="new" title="BFG 1300 (page does not exist)">BFG 1300</a><span class="noprint" style="font-size:85%; font-style: normal;"> [<a href="https://fr.wikipedia.org/wiki/BFG_(entreprise)" class="extiw" title="fr:BFG (entreprise)">fr</a>]</span>, using the air-cooled <a href="/wiki/Citro%C3%ABn_GS#Mechanics" title="Citroën GS">Citroën flat-four</a> car engine. Approximately 450 were built, with one quarter of these purchased by the French police.<sup id="cite_ref-CitroenetBFG_18-0" class="reference"><a href="#cite_note-CitroenetBFG-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-CitroenetBoxer4_19-0" class="reference"><a href="#cite_note-CitroenetBoxer4-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup></li></ul> <div class="mw-heading mw-heading2"><h2 id="Use_in_aircraft">Use in aircraft</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Flat-four_engine&action=edit&section=9" title="Edit section: Use in aircraft"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:ULPower_UL260i.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/2/22/ULPower_UL260i.jpg/220px-ULPower_UL260i.jpg" decoding="async" width="220" height="165" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/22/ULPower_UL260i.jpg/330px-ULPower_UL260i.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/22/ULPower_UL260i.jpg/440px-ULPower_UL260i.jpg 2x" data-file-width="2560" data-file-height="1920" /></a><figcaption><a href="/wiki/ULPower_UL260i" title="ULPower UL260i">ULPower UL260i</a> aircraft engine</figcaption></figure> <p><a href="/wiki/Light_aircraft" title="Light aircraft">Light aircraft</a> commonly use flat-four engines with displacements up to 6.4 L (390 cu in) from manufacturers such as <a href="/wiki/Rotax" title="Rotax">Rotax</a>, <a href="/wiki/Lycoming_Engines" title="Lycoming Engines">Lycoming Engines</a>, <a href="/wiki/Teledyne_Continental_Motors" class="mw-redirect" title="Teledyne Continental Motors">Continental Motors</a> and <a href="/wiki/Franklin_Engine_Company" title="Franklin Engine Company">Franklin Engine Company</a>. </p><p>For <a href="/wiki/Radio-controlled_aircraft" title="Radio-controlled aircraft">radio-controlled aircraft</a>, flat-four engines with displacements of 40–50 cc (2.4–3.1 cu in) are produced by companies such as <a href="/wiki/O.S._Engines" title="O.S. Engines">O.S. Engines</a>. </p><p>A notable recent flat-four aero-engine is the <a href="/wiki/Flathead_engine" title="Flathead engine">side-valve</a> <a href="/wiki/Belgium" title="Belgium">Belgian</a> <a href="/wiki/D-Motor_LF26" title="D-Motor LF26">D-Motor LF26</a>.<sup id="cite_ref-20" class="reference"><a href="#cite_note-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> Although the side-valve format has long been abandoned for most automotive applications because its combustion chamber is a bar to high engine <a href="/wiki/Rpm" class="mw-redirect" title="Rpm">rpm</a>, the massively over-square (1.295:1) D-Motor is a very simple, low-revving, compact, reliable lightweight aero-engine (without the heavy complication of <a href="/wiki/Ohv" class="mw-redirect" title="Ohv">ohv</a> valve-gear)<sup id="cite_ref-21" class="reference"><a href="#cite_note-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Flat-four_engine&action=edit&section=10" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Straight-four_engine" title="Straight-four engine">Straight-four engine</a></li> <li><a href="/wiki/V4_engine" title="V4 engine">V4 engine</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Flat-four_engine&action=edit&section=11" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist reflist-columns references-column-width" style="column-width: 30em;"> <ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text">The so-called "boxer" configuration appears somewhat like boxing competitors punching their gloves together before a fight</span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text">Established manufacturers of such air-cooled aero-engines include <a href="/wiki/Lycoming_Engines" title="Lycoming Engines">Lycoming</a> and <a href="/wiki/Continental_Aerospace_Technologies" title="Continental Aerospace Technologies">Continental</a>.</span> </li> <li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite id="CITEREFNunney2007" class="citation book cs1">Nunney, M. J. (2007). <span class="id-lock-limited" title="Free access subject to limited trial, subscription normally required"><a rel="nofollow" class="external text" href="https://archive.org/details/lightheavyvehicl00nunn_220"><i>Light and Heavy Vehicle Technology</i></a></span>. Butterworth-Heinemann. p. <a rel="nofollow" class="external text" href="https://archive.org/details/lightheavyvehicl00nunn_220/page/n25">13</a>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-7506-8037-0" title="Special:BookSources/978-0-7506-8037-0"><bdi>978-0-7506-8037-0</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Light+and+Heavy+Vehicle+Technology&rft.pages=13&rft.pub=Butterworth-Heinemann&rft.date=2007&rft.isbn=978-0-7506-8037-0&rft.aulast=Nunney&rft.aufirst=M.+J.&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Flightheavyvehicl00nunn_220&rfr_id=info%3Asid%2Fen.wikipedia.org%3AFlat-four+engine" class="Z3988"></span></span> </li> <li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"> Engine article <a rel="nofollow" class="external autonumber" href="https://www.motorauthority.com/news/1111942_whats-the-difference-between-flat-4-and-inline-4-engines">[1]</a></span> </li> <li id="cite_note-Wilson-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-Wilson_5-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFWilson1995" class="citation book cs1">Wilson, Hugo (1995). "The A–Z of Motorcycles". <span class="id-lock-registration" title="Free registration required"><a rel="nofollow" class="external text" href="https://archive.org/details/encyclopediaofmo00wils_1"><i>The Encyclopedia of the Motorcycle</i></a></span>. London, UK: Dorling Kindersley. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-7513-0206-6" title="Special:BookSources/0-7513-0206-6"><bdi>0-7513-0206-6</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=bookitem&rft.atitle=The+A%E2%80%93Z+of+Motorcycles&rft.btitle=The+Encyclopedia+of+the+Motorcycle&rft.place=London%2C+UK&rft.pub=Dorling+Kindersley&rft.date=1995&rft.isbn=0-7513-0206-6&rft.aulast=Wilson&rft.aufirst=Hugo&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Fencyclopediaofmo00wils_1&rfr_id=info%3Asid%2Fen.wikipedia.org%3AFlat-four+engine" class="Z3988"></span></span> </li> <li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text">Thomson. Vibration Theory and Applications. p. 190. Dynamics of reciprocating forces. Prentice Hall Inc., USA, 1965.</span> </li> <li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text">Announcement on Legacy exhaust in Japanese: <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20160515173706/http://www.fhi.co.jp/news/03_04_06/03_05_23b.htm">"Fuji Heavy Industries, Press Information"</a>. 2003-05-23. Archived from <a rel="nofollow" class="external text" href="http://www.fhi.co.jp/news/03_04_06/03_05_23b.htm">the original</a> on 2016-05-15<span class="reference-accessdate">. Retrieved <span class="nowrap">2013-12-16</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Fuji+Heavy+Industries%2C+Press+Information&rft.date=2003-05-23&rft_id=http%3A%2F%2Fwww.fhi.co.jp%2Fnews%2F03_04_06%2F03_05_23b.htm&rfr_id=info%3Asid%2Fen.wikipedia.org%3AFlat-four+engine" class="Z3988"></span></span> </li> <li id="cite_note-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-8">^</a></b></span> <span class="reference-text">Announcement on Forester exhaust in Japanese: <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20160304084234/http://www.fhi.co.jp/news/05_01_03/05_01_27.html">"Fuji Heavy Industries, News Release"</a>. 2005-01-27. Archived from <a rel="nofollow" class="external text" href="http://www.fhi.co.jp/news/05_01_03/05_01_27.html">the original</a> on 2016-03-04<span class="reference-accessdate">. Retrieved <span class="nowrap">2013-12-16</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Fuji+Heavy+Industries%2C+News+Release&rft.date=2005-01-27&rft_id=http%3A%2F%2Fwww.fhi.co.jp%2Fnews%2F05_01_03%2F05_01_27.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AFlat-four+engine" class="Z3988"></span></span> </li> <li id="cite_note-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-9">^</a></b></span> <span class="reference-text">Announcement on Impreza exhaust in Japanese: <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20160309183635/http://www.fhi.co.jp/news/07_04_06/07_06_05_01.html">"Fuji Heavy Industries, News Release"</a>. 2007-06-05. Archived from <a rel="nofollow" class="external text" href="http://www.fhi.co.jp/news/07_04_06/07_06_05_01.html">the original</a> on 2016-03-09<span class="reference-accessdate">. Retrieved <span class="nowrap">2013-12-16</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Fuji+Heavy+Industries%2C+News+Release&rft.date=2007-06-05&rft_id=http%3A%2F%2Fwww.fhi.co.jp%2Fnews%2F07_04_06%2F07_06_05_01.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AFlat-four+engine" class="Z3988"></span></span> </li> <li id="cite_note-10"><span class="mw-cite-backlink"><b><a href="#cite_ref-10">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20190423025054/http://www.american-automobiles.com/Buffum.html">"The Buffum Automobile"</a>. Farber and Associates. Archived from <a rel="nofollow" class="external text" href="http://www.american-automobiles.com/Buffum.html">the original</a> on 2019-04-23<span class="reference-accessdate">. Retrieved <span class="nowrap">2019-10-27</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=The+Buffum+Automobile&rft.pub=Farber+and+Associates&rft_id=http%3A%2F%2Fwww.american-automobiles.com%2FBuffum.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AFlat-four+engine" class="Z3988"></span></span> </li> <li id="cite_note-11"><span class="mw-cite-backlink"><b><a href="#cite_ref-11">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation news cs1"><a rel="nofollow" class="external text" href="https://www.theglobeandmail.com/globe-drive/reviews/classics/the-engine-that-benz-built-still-survives/article4317376/">"The engine that Benz built still survives"</a>. <i>The Globe and Mail</i>. 29 April 2010<span class="reference-accessdate">. Retrieved <span class="nowrap">1 September</span> 2019</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=The+Globe+and+Mail&rft.atitle=The+engine+that+Benz+built+still+survives&rft.date=2010-04-29&rft_id=https%3A%2F%2Fwww.theglobeandmail.com%2Fglobe-drive%2Freviews%2Fclassics%2Fthe-engine-that-benz-built-still-survives%2Farticle4317376%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AFlat-four+engine" class="Z3988"></span></span> </li> <li id="cite_note-popsci-12"><span class="mw-cite-backlink">^ <a href="#cite_ref-popsci_12-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-popsci_12-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFStepler1994" class="citation journal cs1">Stepler, Richard (September 1994). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=RudyJP1ByycC&pg=PA44">"Preview Drive: Three Ways to Get a Grip"</a>. <i>Popular Science</i>. <b>245</b> (3): 44<span class="reference-accessdate">. Retrieved <span class="nowrap">2011-10-23</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Popular+Science&rft.atitle=Preview+Drive%3A+Three+Ways+to+Get+a+Grip&rft.volume=245&rft.issue=3&rft.pages=44&rft.date=1994-09&rft.aulast=Stepler&rft.aufirst=Richard&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DRudyJP1ByycC%26pg%3DPA44&rfr_id=info%3Asid%2Fen.wikipedia.org%3AFlat-four+engine" class="Z3988"></span></span> </li> <li id="cite_note-Bonk-13"><span class="mw-cite-backlink"><b><a href="#cite_ref-Bonk_13-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFBonk2013" class="citation web cs1">Bonk, Aaron (2013-02-07) (2013-02-07). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20140227052947/http://www.superstreetonline.com/techarticles/sstp_1301_how_boxer_engines_work/">"How Boxer Engines Work, And Why You Should Care About Subaru's New FA20"</a>. Archived from <a rel="nofollow" class="external text" href="http://www.superstreetonline.com/techarticles/sstp_1301_how_boxer_engines_work/">the original</a> on 2014-02-27<span class="reference-accessdate">. Retrieved <span class="nowrap">8 January</span> 2014</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=How+Boxer+Engines+Work%2C+And+Why+You+Should+Care+About+Subaru%27s+New+FA20&rft.date=2013-02-07&rft.aulast=Bonk&rft.aufirst=Aaron+%282013-02-07%29&rft_id=http%3A%2F%2Fwww.superstreetonline.com%2Ftecharticles%2Fsstp_1301_how_boxer_engines_work%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AFlat-four+engine" class="Z3988"></span><span class="cs1-maint citation-comment"><code class="cs1-code">{{<a href="/wiki/Template:Cite_web" title="Template:Cite web">cite web</a>}}</code>: CS1 maint: numeric names: authors list (<a href="/wiki/Category:CS1_maint:_numeric_names:_authors_list" title="Category:CS1 maint: numeric names: authors list">link</a>)</span></span> </li> <li id="cite_note-14"><span class="mw-cite-backlink"><b><a href="#cite_ref-14">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.porsche.com/canada/en/models/718/718-boxster/drive/performance/">"Performance: The new 718 Boxster"</a>. Porsche. 2016<span class="reference-accessdate">. Retrieved <span class="nowrap">2016-11-01</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Performance%3A+The+new+718+Boxster&rft.pub=Porsche&rft.date=2016&rft_id=http%3A%2F%2Fwww.porsche.com%2Fcanada%2Fen%2Fmodels%2F718%2F718-boxster%2Fdrive%2Fperformance%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AFlat-four+engine" class="Z3988"></span></span> </li> <li id="cite_note-15"><span class="mw-cite-backlink"><b><a href="#cite_ref-15">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.caranddriver.com/porsche/718-cayman">"2019 Porsche 718 Cayman"</a>. <i>www.caranddriver.com</i>. 14 May 2019<span class="reference-accessdate">. Retrieved <span class="nowrap">1 September</span> 2019</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=www.caranddriver.com&rft.atitle=2019+Porsche+718+Cayman&rft.date=2019-05-14&rft_id=https%3A%2F%2Fwww.caranddriver.com%2Fporsche%2F718-cayman&rfr_id=info%3Asid%2Fen.wikipedia.org%3AFlat-four+engine" class="Z3988"></span></span> </li> <li id="cite_note-16"><span class="mw-cite-backlink"><b><a href="#cite_ref-16">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.evo.co.uk/porsche/718-cayman">"Porsche 718 Cayman review – The entry-level Porsche punches above its weight"</a>. <i>www.evo.co.uk</i><span class="reference-accessdate">. Retrieved <span class="nowrap">1 September</span> 2019</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=www.evo.co.uk&rft.atitle=Porsche+718+Cayman+review+%E2%80%93+The+entry-level+Porsche+punches+above+its+weight&rft_id=https%3A%2F%2Fwww.evo.co.uk%2Fporsche%2F718-cayman&rfr_id=info%3Asid%2Fen.wikipedia.org%3AFlat-four+engine" class="Z3988"></span></span> </li> <li id="cite_note-17"><span class="mw-cite-backlink"><b><a href="#cite_ref-17">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.motortrend.com/cars/porsche/718-cayman/2017/2017-porsche-718-cayman-first-drive-review/">"2017 Porsche 718 Cayman First Drive Review: Performance Trumps Sound"</a>. <i>www.motortrend.com</i><span class="reference-accessdate">. Retrieved <span class="nowrap">1 September</span> 2019</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=www.motortrend.com&rft.atitle=2017+Porsche+718+Cayman+First+Drive+Review%3A+Performance+Trumps+Sound&rft_id=https%3A%2F%2Fwww.motortrend.com%2Fcars%2Fporsche%2F718-cayman%2F2017%2F2017-porsche-718-cayman-first-drive-review%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AFlat-four+engine" class="Z3988"></span></span> </li> <li id="cite_note-CitroenetBFG-18"><span class="mw-cite-backlink"><b><a href="#cite_ref-CitroenetBFG_18-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFJulian_Marsh2000" class="citation web cs1">Julian Marsh (2000-06-10). <a rel="nofollow" class="external text" href="http://www.citroenet.org.uk/miscellaneous/bfg/bfg.htm">"BFG and MF motorcycles"</a>. Citroenet.org.uk<span class="reference-accessdate">. Retrieved <span class="nowrap">2011-12-06</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=BFG+and+MF+motorcycles&rft.pub=Citroenet.org.uk&rft.date=2000-06-10&rft.au=Julian+Marsh&rft_id=http%3A%2F%2Fwww.citroenet.org.uk%2Fmiscellaneous%2Fbfg%2Fbfg.htm&rfr_id=info%3Asid%2Fen.wikipedia.org%3AFlat-four+engine" class="Z3988"></span></span> </li> <li id="cite_note-CitroenetBoxer4-19"><span class="mw-cite-backlink"><b><a href="#cite_ref-CitroenetBoxer4_19-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFJulian_Marsh" class="citation web cs1">Julian Marsh. <a rel="nofollow" class="external text" href="http://www.citroenet.org.uk/passenger-cars/michelin/gs/flat-4/engine.html">"GS & GSA boxer engine"</a>. Citroenet.org.uk<span class="reference-accessdate">. Retrieved <span class="nowrap">2011-12-06</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=GS+%26+GSA+boxer+engine&rft.pub=Citroenet.org.uk&rft.au=Julian+Marsh&rft_id=http%3A%2F%2Fwww.citroenet.org.uk%2Fpassenger-cars%2Fmichelin%2Fgs%2Fflat-4%2Fengine.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AFlat-four+engine" class="Z3988"></span></span> </li> <li id="cite_note-20"><span class="mw-cite-backlink"><b><a href="#cite_ref-20">^</a></b></span> <span class="reference-text">A modular variant of the LF26 is the 4-litre <a href="/wiki/Flat-six" class="mw-redirect" title="Flat-six">flat-six</a> <a href="/wiki/D-Motor_LF39" title="D-Motor LF39">D-Motor LF39</a></span> </li> <li id="cite_note-21"><span class="mw-cite-backlink"><b><a href="#cite_ref-21">^</a></b></span> <span class="reference-text">Note: A low-revving engine is eminently suitable to drive a propeller, which is typically most effective at about 2,000 rpm. If a valve in a side-valve engine should stick open, it cannot hit the piston and cause engine failure; the engine will continue with just that cylinder inoperative. 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href="/wiki/Template:Piston_engine_configurations" title="Template:Piston engine configurations"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Piston_engine_configurations" title="Template talk:Piston engine configurations"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Piston_engine_configurations" title="Special:EditPage/Template:Piston engine configurations"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Engine_configurations_for_piston_engines126" style="font-size:114%;margin:0 4em"><a href="/wiki/Engine_configuration" title="Engine configuration">Engine configurations</a> for <a href="/wiki/Piston_engine" class="mw-redirect" title="Piston engine">piston engines</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">Type</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Newcomen_atmospheric_engine" title="Newcomen atmospheric engine">Atmospheric</a></li> <li><a href="/wiki/Axial_engine" title="Axial engine">Axial</a></li> <li><a href="/wiki/Beam_engine" title="Beam engine">Beam</a> <ul><li><a href="/wiki/Cornish_steam_engine" class="mw-redirect" title="Cornish steam engine">Cornish</a></li> <li><a href="/wiki/Rotative_beam_engine" class="mw-redirect" title="Rotative beam engine">Rotative</a></li></ul></li> <li><a href="/wiki/Bourke_engine" title="Bourke engine">Bourke</a></li> <li><a href="/wiki/Cam_engine" title="Cam engine">Cam engine</a></li> <li><a href="/wiki/Camless_piston_engine" title="Camless piston engine">Camless</a></li> <li><a href="/wiki/Compound_steam_engine" title="Compound steam engine">Compound</a></li> <li><a href="/wiki/Double-acting_cylinder" class="mw-redirect" title="Double-acting cylinder">Double-acting cylinder</a></li> <li><a href="/wiki/Flathead_engine" title="Flathead engine">Flathead</a></li> <li><a href="/wiki/Free-piston_engine" title="Free-piston engine">Free-piston</a> <ul><li><a href="/wiki/Stelzer_engine" title="Stelzer engine">Stelzer</a></li></ul></li> <li><a href="/wiki/Hemi_engine" class="mw-redirect" title="Hemi engine">Hemi</a></li> <li><a href="/wiki/Heron_cylinder_head" title="Heron cylinder head">Heron head</a></li> <li><a href="/wiki/IOE_engine" title="IOE engine">Intake over exhaust</a></li> <li><a href="/wiki/Oscillating_cylinder_steam_engine" title="Oscillating cylinder steam engine">Oscillating cylinder</a></li> <li><a href="/wiki/Opposed-piston_engine" title="Opposed-piston engine">Opposed-piston</a></li> <li><a href="/wiki/Overhead_camshaft_engine" title="Overhead camshaft engine">Overhead camshaft</a></li> <li><a href="/wiki/Overhead_valve_engine" title="Overhead valve engine">Overhead valve</a></li> <li><a href="/wiki/Pent-roof_combustion_chamber" title="Pent-roof combustion chamber">Pentroof</a></li> <li><a href="/wiki/Rotary_engine" title="Rotary engine">Rotary</a></li> <li><a href="/wiki/Single-acting_cylinder" class="mw-redirect" title="Single-acting cylinder">Single-acting cylinder</a></li> <li><a href="/wiki/Split_cycle_engine" class="mw-redirect" title="Split cycle engine">Split cycle</a></li> <li><a href="/wiki/Swing-piston_engine" title="Swing-piston engine">Swing-piston</a></li> <li><a href="/wiki/Uniflow_steam_engine" title="Uniflow steam engine">Uniflow</a></li> <li><a href="/wiki/Watt_steam_engine" title="Watt steam engine">Watt</a></li> <li><a href="/wiki/Chrysler_wedge_engine" class="mw-redirect" title="Chrysler wedge engine">Wedge</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Stroke_(engine)" title="Stroke (engine)">Stroke cycles</a></th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Two-stroke_engine" title="Two-stroke engine">Two-stroke</a></li> <li><a href="/wiki/Four-stroke_engine" title="Four-stroke engine">Four-stroke</a></li> <li><a href="/wiki/Five-stroke_engine" title="Five-stroke engine">Five-stroke</a></li> <li><a href="/wiki/Six-stroke_engine" title="Six-stroke engine">Six-stroke</a></li> <li><a href="/wiki/Two-_and_four-stroke_engines" title="Two- and four-stroke engines">Two-and four-stroke</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Engine_configuration" title="Engine configuration">Cylinder layouts</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:10em"><a href="/wiki/Straight_engine" title="Straight engine">Inline / straight</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Single-cylinder_engine" title="Single-cylinder engine">I1</a></li> <li><a href="/wiki/Straight-twin_engine" title="Straight-twin engine">I2</a></li> <li><a href="/wiki/Straight-three_engine" title="Straight-three engine">I3</a></li> <li><a href="/wiki/Straight-four_engine" title="Straight-four engine">I4</a></li> <li><a href="/wiki/Straight-five_engine" title="Straight-five engine">I5</a></li> <li><a href="/wiki/Straight-six_engine" title="Straight-six engine">I6</a></li> <li><a href="/wiki/Straight-seven_engine" title="Straight-seven engine">I7</a></li> <li><a href="/wiki/Straight-eight_engine" title="Straight-eight engine">I8</a></li> <li><a href="/wiki/Straight-nine_engine" title="Straight-nine engine">I9</a></li> <li><a href="/wiki/Straight-twelve_engine" title="Straight-twelve engine">I12</a></li> <li><a href="/wiki/Straight-fourteen_engine" title="Straight-fourteen engine">I14</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:10em"><a href="/wiki/Flat_engine" title="Flat engine">Flat / boxer</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Flat-twin_engine" title="Flat-twin engine">F2</a></li> <li><a class="mw-selflink selflink">F4</a></li> <li><a href="/wiki/Flat-six_engine" title="Flat-six engine">F6</a></li> <li><a href="/wiki/Flat-eight_engine" title="Flat-eight engine">F8</a></li> <li><a href="/wiki/Flat-ten_engine" title="Flat-ten engine">F10</a></li> <li><a href="/wiki/Flat-twelve_engine" title="Flat-twelve engine">F12</a></li> <li><a href="/wiki/Flat-sixteen_engine" title="Flat-sixteen engine">F16</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:10em"><a href="/wiki/V_engine" title="V engine">V / Vee</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/V-twin_engine" title="V-twin engine">V2</a></li> <li><a href="/wiki/V3_engine" title="V3 engine">V3</a></li> <li><a href="/wiki/V4_engine" title="V4 engine">V4</a></li> <li><a href="/wiki/V5_engine" title="V5 engine">V5</a> <ul><li><a href="/wiki/VR5_engine" title="VR5 engine">VR5</a></li></ul></li> <li><a href="/wiki/V6_engine" title="V6 engine">V6</a> <ul><li><a href="/wiki/VR6_engine" title="VR6 engine">VR6</a></li></ul></li> <li><a href="/wiki/V8_engine" title="V8 engine">V8</a></li> <li><a href="/wiki/V10_engine" title="V10 engine">V10</a></li> <li><a href="/wiki/V12_engine" title="V12 engine">V12</a></li> <li><a href="/wiki/V14_engine" title="V14 engine">V14</a></li> <li><a href="/wiki/V16_engine" title="V16 engine">V16</a></li> <li><a href="/wiki/V18_engine" title="V18 engine">V18</a></li> <li><a href="/wiki/V20_engine" title="V20 engine">V20</a></li> <li><a href="/wiki/V24_engine" title="V24 engine">V24</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:10em"><a href="/wiki/W_engine" title="W engine">W</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/W_engine#W3_engines" title="W engine">W3</a></li> <li><a href="/wiki/W_engine#W6_engines" title="W engine">W6</a></li> <li><a href="/wiki/W8_engine" title="W8 engine">W8</a></li> <li><a href="/wiki/W12_engine" title="W12 engine">W12</a></li> <li><a href="/wiki/W16_engine" title="W16 engine">W16</a></li> <li><a href="/wiki/W18_engine" title="W18 engine">W18</a></li> <li><a href="/wiki/W_engine#W24_engine" title="W engine">W24</a></li> <li><a href="/wiki/W_engine#W30_engine" title="W engine">W30</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:10em">Other</th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Napier_Deltic" title="Napier Deltic">Deltic</a></li> <li><a href="/wiki/H_engine" title="H engine">H</a></li> <li><a href="/wiki/Radial_engine" title="Radial engine">Radial</a></li> <li><a href="/wiki/Split-single_engine" title="Split-single engine">Split-single</a></li> <li><a href="/wiki/U_engine" title="U engine">U</a></li> <li><a href="/wiki/X_engine" title="X engine">X</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr></tbody></table></div>    </div><noscript><img src="https://login.wikimedia.org/wiki/Special:CentralAutoLogin/start?useformat=desktop&type=1x1&usesul3=0" alt="" width="1" height="1" style="border: none; position: absolute;"></noscript> <div class="printfooter" data-nosnippet="">Retrieved from "<a dir="ltr" href="https://en.wikipedia.org/w/index.php?title=Flat-four_engine&oldid=1264397640">https://en.wikipedia.org/w/index.php?title=Flat-four_engine&oldid=1264397640</a>"</div></div> <div id="catlinks" class="catlinks" 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