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[[File:Marine Hemi.JPG|thumb|The Chrysler Marine Hemis were popular in wooden boats such as the [[Chris-Craft Boats|Chris-Craft]] during the 1950s and 1960s]]
The '''Chrysler Hemi
Although Chrysler is most identified with the use of "Hemi" as a marketing term, many other auto manufacturers have incorporated similar cylinder head designs. The engine block and cylinder heads were cast and manufactured at [[Indianapolis Foundry]].{{which|date=May 2024}}{{when|date=May 2024}}{{cn|date=May 2024}}
During the 1970s and 1980s, Chrysler also used the ''Hemi'' name for their Australian-made [[Chrysler Hemi-6 Engine|Hemi-6 Engine]], and applied it to the 4-cylinder [[Astron 2.6|Mitsubishi 2.6L engine]] installed in various North American market vehicles.▼
▲During the 1970s and 1980s, Chrysler also
==Design==
{{main|Hemispherical combustion chamber}}
A [[hemispherical combustion chamber]] is an efficient shape, with an excellent surface-to-volume ratio, minimal heat loss to the [[cylinder head]], and room for two large [[poppet valve|valves]]. However, it allows no more than two valves per cylinder, and these large valves are necessarily heavier than in a [[multi-valve]] engine. The intake and exhaust valves lie on opposite sides of the chamber and necessitate a "[[Crossflow cylinder head|cross-flow]]" head design. As the combustion chamber is a partial hemisphere, a flat-topped piston would yield too low a [[compression ratio]] unless a very long stroke is used, so to attain the desired compression ratio the piston crown is domed to protrude into the head at top dead center. The result is a combustion chamber in the shape of the space between where the domed piston stops and the dome shape in the head receiving it.▼
The main advantage of a hemi head engine over other head designs is power. In return, hemi head engines tend to have complex valve trains, are expensive to build, and both larger and heavier than conventional designs.
The hemi-head design places the [[spark plug]] at or near the center of the chamber to promote a strong flame front. However, if the hemi-head hemisphere is of equal diameter to the piston, there is minimal [[Squish (piston engine)|squish]] for proper turbulence to mix fuel and air thoroughly. Thus, hemi-heads, because of their lack of squish, are more sensitive to fuel [[octane rating]]; a given compression ratio will require a higher octane rating to avoid pre-[[detonation]] in a hemi engine than in some conventional engine designs such as the wedge and bathtub.▼
▲A [[hemispherical combustion chamber]] is an efficient shape, with an excellent surface-to-volume ratio, {{clarification needed span|text=minimal heat loss to the [[cylinder head]],|reason=How, and why? A hemisphere has the largest possible area (of any combustion chamber shape of a given diameter); why doesn't it transfer (i.e. lose) more heat than any other smaller shape? In layman's terms, with a reliable citation, please.|date=May 2024}} and room for two large [[poppet valve|valves]]. However, it allows no more than two valves per cylinder,{{why|date=May 2024}} and these large valves are necessarily heavier than in a [[multi-valve]] engine. The intake and exhaust valves lie on opposite sides of the chamber and necessitate a "[[Crossflow cylinder head|cross-flow]]" head design. As the combustion chamber is a partial hemisphere, a flat-topped piston would yield too low a [[compression ratio]] unless a very long stroke is used, so to attain the desired compression ratio the piston crown is domed to protrude into the head at top dead center. The result is a combustion chamber in the shape of the space between where the domed piston stops and the dome shape in the head receiving it.
▲The hemi-head design places the [[spark plug]] at or near the center of the chamber to promote a strong flame front. However, if the hemi-head hemisphere is of equal diameter to the piston, there is minimal [[Squish (piston engine)|squish]] for proper turbulence to mix fuel and air thoroughly. Thus, hemi-heads, because of their lack of squish, are more sensitive to fuel [[octane rating]]; a given compression ratio will require a higher octane rating to avoid
The hemi head always has intake and exhaust valve stems that point in different directions, requiring a large, wide cylinder head and complex [[rocker arm]] geometry in both [[cam-in-block]] and [[single overhead cam]] engines (dual overhead cam engines may not have rocker arms). This adds to the overall width of the engine, limiting the vehicles in which it can be installed.
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Significant challenges in the commercialization of engine designs using hemispherical chambers revolved around the valve actuation, specifically how to make it effective, efficient, and reliable at an acceptable cost.<ref name="Allpar">{{cite web |title=Origin of the Mopar Hemi engine, Ardun Heads, and Riley cars |url=https://www.allpar.com/threads/origin-of-the-mopar-hemi-engine-ardun-heads-and-riley-cars.229942/#post-1085224040 |website=Allpar Forums |access-date=March 14, 2022 |date=November 16, 2020}}</ref> This complexity was referenced early in Chrysler's development of their 1950s hemi engine: the head was referred to in company advertising as the ''Double Rocker Shaft'' head.<ref name="Allpar"/>
{{anchor|First}}▼
==First generation: FirePower 1951–1958== <!-- Other articles link here. -->▼
Chrysler developed
In addition to the aircraft engine, Chrysler and [[Continental Motors Company|Continental]] worked together to develop the air-cooled [[Continental AV1790|AV-1790-5B]] V12 Hemi engine used in the [[M47 Patton]] tank.
▲{{anchor|First}}
Chrysler applied their military experience with the hemispherical combustion chamber to
▲==First generation: FirePower 1951–1958==<!-- Other articles link here. -->
▲Chrysler applied their military experience with the hemispherical combustion chamber to their first [[Overhead valve engine|overhead-valve]] [[V8 engine]], released under the name '''FirePower''', not "Hemi," in 1950 for the 1951 model year. The first version of the FirePower engine had a displacement of {{convert|331|cuin|L|1|abbr=on}} and produced {{convert|180|bhp|kW|1|abbr=on}}. Eventually, three of the four Chrysler divisions had their own version of the FirePower engine, with different displacements and designations, and having almost no parts in common. This lack of commonality was due in part to the three engine versions using different bore pitches (the center-to-center distance between adjacent cylinders). Chrysler and [[Imperial_(automobile)#First_generation_(1955–1956):_A_separate_make|Imperial]] called their versions the ''FirePower''. [[DeSoto (automobile)|DeSoto]] called theirs the ''FireDome''. Dodge had a smaller version, known as the ''Red Ram''. Only [[Plymouth (automobile)|Plymouth]] did not have a version, but retained the Dodge [[Polyspheric|poly-head engines]]. There was no Plymouth Hemi engine until the 1964 [[426 Hemi|426]].
[[Briggs Cunningham]] used the Chrysler version in some of his [[race car]]s for international motorsports. A Chrysler-powered [[B. S. Cunningham Company#C-5R|Cunningham C-5R]] won its class in 1953. Cunningham switched away from these designs in 1959 when Chrysler temporarily abandoned the hemispherical concept in favor of the wedge-head [[Chrysler B engine|B engine]] until 1964. [[Carl Kiekhaefer]] also used the Chrysler engines in NASCAR cars owned by him from 1955 and 1956, winning the [[NASCAR Cup Series|Grand National Series]] championship both years.
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==== 345 ====
The largest DeSoto engine for 1957 was the DeSoto Adventurer offering {{convert|344.6|cuin|L|1|abbr=on}} with square bore and stroke dimensions of 3.80 inches. The DeSoto Adventurer used dual Carter WCFB four-barrel carburetors for a rating of {{convert|345|bhp|kW|0|abbr=on}}, producing one horsepower per cubic inch (the first American car to do so as standard equipment)
=== Dodge ===
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{{Infobox automobile engine
| name = 426
| image =
| caption = 426 Hemi
| manufacturer = [[Chrysler]]
| aka = Elephant engine
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}}
The [[hemispherical]] head design was revived in 1964
The 426 Hemi of the 1960s was an engine produced for use in [[NASCAR]], as raced in a [[Plymouth Belvedere]] in 1964. It was not initially available to the general buying public. The 426 Hemi was not allowed to compete in NASCAR's 1965 season due to its unavailability in production vehicles sold to the general public and because of complaints by Ford regarding its power. However several special production versions of the [[Dodge Dart]], the [[Plymouth Fury]], and later, in 1965, the [[Dodge Coronet]], were produced with aluminum [[Fender (vehicle)|fenders]] and [[Bumper (car)|bumpers]] for [[drag racing]] and made available to the general public.
Chrysler introduced the "Street
There were many differences between the Hemi and the 426 Wedge-head
The 426 Hemi, in "
The
[[File:1966 Dodge Charger 426 Hemi engine.JPG|thumb|426 Hemi engine in a 1966 Charger]]
The street version of the second generation Hemi engine was used (optionally, in all but the last case) in the following vehicles:
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* 1968 [[Plymouth Barracuda#Second generation (1967–1969)|Plymouth Barracuda]]
* 1968–1971 [[Dodge Super Bee]]
*
*1969 [[Dodge Charger|Dodge Charger R/T]]
* 1969 [[Dodge Charger Daytona]]
* 1970 [[Plymouth Superbird]]
* 1970–1971 [[Plymouth Barracuda#
* 1970–1971 [[Dodge Challenger]]
* 1970 [[Monteverdi Hai 450]]
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{{expand section|appropriately cited content on the 426 Hemi in drag racing, where it was a dominant force|date=May 2024}}
There were many differences between the racing Hemis and the street
The 426 Hemi also was used in [[NHRA]] and AHRA drag racing. Its large [[casting]] allowed the engine to be overbored and stroked to [[Engine displacement|displacements]] unattainable in the other engines of the day.{{cn|date=May 2024}}
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Engines mated to the six-speed manual transmission or used in the Ram Heavy Duty did not feature the [[Multi-Displacement System]] (MDS). The new version of the 5.7 L had five different camshaft profiles, all with VCT:
* Active intake with MDS▼
* Active intake without MDS
*
* Passive intake without MDS
* HEV application (modified version of passive intake with MDS)
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===6.2 Hellcat{{Anchor|6.2|6.2 L|Hellcat|Turbocharged}}===
For 2015, Chrysler introduced an all-new high performance [[supercharger|supercharged]] variant of the Hemi engine, called the '''Hellcat''' (named after the [[Grumman F6F Hellcat]]).<ref name=enginelabs /> It features the same {{convert|4.09|in|mm|abbr=on|1}} bore as the 6.4 L Hemi and the same {{convert|3.578|in|mm|abbr=on|1}} stroke as the 5.7 L, giving it a total displacement of {{convert|6166|cc|L cuin|1|abbr=on}}.<ref name=enginelabs /> The supercharger is a {{convert|2380|cc|cuin|abbr=on}} [[twin-screw supercharger|twin-screw]] [[IHI Corporation|IHI]] unit with integrated [[charge cooler]]s, capable of producing {{convert|11.6|psi|kPa bar|abbr=on}} of boost.<ref name=SAE /> This engine is rated at {{convert|707|bhp|PS kW|abbr=on}} at 6,000 rpm and {{convert|650|lbft|Nm|0|abbr=on}} at 4,000 rpm of torque<ref name=enginelabs /> and has a [[compression ratio]] of 9.5:1.<ref name=enginelabs>{{cite web|last1=Magda|first1=Mike|title=SRT Engineer Explains How Hellcat Hemi Pulls 717 Horsepower|url=http://www.enginelabs.com/news/hellcat-hemi-chief-engineer-provides-engine-details/|website=enginelabs.com|date=July 24, 2014 |access-date=November 4, 2014}}</ref> This engine was the most powerful engine produced by [[Chrysler]] as well as the most powerful production engine ever in a [[muscle car]] until the Dodge Demon was introduced.<ref name=SAE /> This engine is not equipped with Chrysler's [[Multi-Displacement System]].<ref name=SAE>{{cite web|title=Chrysler's new Hellcat V8 gets 707-hp SAE rating|url=http://articles.sae.org/13227/|website=SAE International |publisher=[[SAE International|SAE]]|access-date=November 4, 2014}}</ref> In 2017, Mopar announced that it would sell it as a [[crate engine]] under the name Hellcrate.<ref>[http://www.roadandtrack.com/motorsports/a13117952/hellcrate-dodge-hellcat-crate-engine-info-pricing/ You Can Buy a 707-HP Hellcat Crate Engine Directly From Mopar] - Brian Silvestro, Road and Track, October 30, 2017</ref> A Redeye version with {{convert|797|hp|PS kW|abbr=on}} debuted in the Dodge Challenger in 2019, followed by the Dodge Charger in 2021.
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