Editing Straight-four engine (section)

{{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>