Editing Straight-eight engine (section)

{{About|the eight-cylinder engine|the 8 mm motion picture film format (STRAIGHT EIGHT)|Filmo#History}}
{{Redirect|Straight eight|the filmmaking event|Straight 8|the 1920s luxury car|Leyland Eight}}
{{Short description|Inline piston engine with eight cylinders}}
{{More citations needed|date=July 2009}}
[[File:Delage engine.JPG|thumb|upright=1.36|[[Delage]] straight-eight racing engine]]
[[File:Inline 8 Cylinder with firing order 1-4-7-3-8-5-2-6.gif|thumb|Straight-eight engine with firing order 1-4-7-3-8-5-2-6]]
The '''straight-eight engine''' or '''inline-eight engine''' (often abbreviated as '''I8''') is an eight-cylinder [[internal combustion engine]] with all eight [[cylinder (engine)|cylinders]] mounted in a straight line along the [[crankcase]]. The type has been produced in [[side-valve]], [[IOE engine|IOE]], [[overhead-valve]], [[sleeve-valve]], and [[overhead-cam]] configurations.

A straight-eight can be timed for [[engine balance#Inherent mechanical balance|inherent primary and secondary balance]], with no unbalanced primary or secondary forces or moments. However, [[crankshaft]] [[torsional vibration]], present to some degree in all engines, is sufficient to require the use of a [[harmonic damper]] at the accessory end of the crankshaft. Without such damping, [[fatigue (material)|fatigue cracking]] near the rear [[main bearing]] [[journal (mechanical device)|journal]] may occur, leading to engine failure.

Although an [[inline-six engine|inline six]]-cylinder engine can also be timed for inherent primary and secondary balance, a straight-eight develops more power strokes per revolution and, as a result, will run more smoothly under load than an inline six. Also, due to the even number of power strokes per revolution, a straight-eight does not produce unpleasant odd-order harmonic vibration in the vehicle's [[driveline]] at low engine speeds.

The smooth running characteristics of the straight-eight made it popular in luxury and racing cars of the past. However, the engine's length demanded the use of a long engine compartment, making the basic design unacceptable in modern vehicles.<ref>{{cite book|last=Moore|first=Stephen J.|title=A Detailed History of the Straight-Eight Automobile Engine|publisher=Self-published on USB|year=2020|isbn=978-0-473-54810-0}}</ref> Also, due to the length of the engine, torsional vibration in both crankshaft and [[camshaft]] can adversely affect reliability and performance at high speeds. In particular, a phenomenon referred to as "crankshaft whip," caused by the effects of [[centrifugal force]] on the crank throws at high engine [[Revolutions per minute|rpm]], can cause physical contact between the [[connecting rod]]s and [[crankcase]] walls, leading to the engine's destruction. As a result, the design has been displaced almost completely by the shorter [[V8 engine]] configuration.