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The [[hemispherical]] head design was revived in 1964. Thesefor werea big-block {{convert|426|cuin|L|1|abbr=on}} overhead valve V8, the first enginesengine officially"Hemi" designatedby HemiChrysler, a name [[Chrysler]]it had trademarked. (and not to be confused with the Chrysler Hemi[[Chrysler enginesRB ofengine#426 thisWedge|426 generationWedge]]. (sometimes Sometimes retroactively referred to as the "Gen 2" or "2G" Hemi,<ref>{{cite web|url=http://www.kolossochryslerjeepdodgeramwi.com/2009-mopar-performance-catalog.htm|title=Kolosso Chrysler Dodge Jeep Ram - New Chrysler, Dodge, Jeep, Ram dealership in Appleton, WI 54914|date=March 14, 2016|url-status=dead|archive-url=https://web.archive.org/web/20160314081951/http://www.kolossochryslerjeepdodgeramwi.com/2009-mopar-performance-catalog.htm|archive-date=March 14, 2016}}</ref>) displaced {{convert|426|cuin|L|1|abbr=on}}. Thethe 426 Hemi was nicknamed the "elephant engine" at the time, a reference to its high power, heavy weight, and large physical dimensions.<ref>[https://www.motortrend.com/how-to/what-is-a-hellephant-crate-engine/ "What Is a Hellephant and Why Are They So Rare?"], ''Motor Trend'', Feb 11, 2021|"That's the nickname given to the second-generation Hemi that came out in race-only form in 1964, then in street form in 1966 as the "Street Hemi". It got the name "elephant engine" due to its large size, heavy weight, and prodigious, ground-pounding power.""</ref> Its {{convert|10.72|in|mm|1|abbr=on}} deck height and {{convert|4.80|in|mm|1|abbr=on}} bore spacing made it the biggest engine in racing at the time.
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" Hemi" in 1966 for its intermediate range of cars and sold the required number of Hemi engines to the public to [[homologation|homologate]] its use for stock car racing in NASCAR events in 1966. The "Street Hemi" was similar to the race Hemi but with dual inline 4four-bblbarrel [[Carter Carburetor|Carter AFB carburetor]]s{{clarification needed|reason=What did the race 426 carburetorshave?}} (with automatic choke), lower compression (10.25:1 from 12.5:1) and lower-lift [[camshaft]], with iron exhaust manifolds instead of lighter steel long tube headers.{{citation needed|date=September 2018}}
There were many differences between the Hemi and the 426 Wedge-head big-block, including main [[cross-bolted bearing|cross-bolted main bearing caps]]{{which|Which capsengine was cross-bolted?}} and a different head bolt pattern. Although all manufacturers were familiar with [[multi-valve]] engines and [[hemispherical combustion chamber]]s, adding more valves per [[Cylindercylinder (engine)|cylinder]] and designing the complex [[valvetrain]] they require were expensive ways of improving the high–[[Revolutions per minute|revolutions per minute]] (rpm)]] breathing of [[production vehicle]]s. By canting the angle of the NASCAR-mandated two valves per cylinder, significantly larger valves could be used. The Chrysler 426 Hemi and all Chrysler [[Chrysler RB engine|RB]]s had [[oversquare]] bore and strokes., Specifically,both the 426 Hemi and [[Chrysler RB engine#426 Wedge|426 Wedge]] hadhaving a [[Bore (engine)|bore]] × [[Stroke (engine)|stroke]] of {{convert|4+1/4x3+3/4|in|mm|1|abbr=on}}.
The 426 Hemi, in "streetStreet Hemi" form, was produced for consumer automobiles from 1966 through 1971. Hemi-powered Dodge and Plymouth cars produced in the model years of 1966 through 1971 have become collector's items. For example, a 1971 Plymouth Barracuda Convertible equipped with the 426 Hemi engine sold at auction for US$3.5 million in 2014.<ref>{{cite web|url=https://www.youtube.com/watch?v=W5tQm8HBB2Y| archive-url=https://ghostarchive.org/varchive/youtube/20211028/W5tQm8HBB2Y| archive-date=2021-10-28|title=MECUM SOLD $3.5 Million - 1971 Plymouth Hemi Cuda Convertible|last=Mecum Auctions|date=June 14, 2014|via=YouTube}}{{cbignore}}</ref>
The street"Street Hemi" version was rated at {{convert|425|bhp|PS kW|0|abbr=on}} at 5000 rpm [[Horsepower#SAE gross power|SAE gross]] and {{convert|490|lbft|Nm|0|abbr=on}} at 4000 rpm of torque equipped with a pair of four-barrel [[Carter Carburetor|Carter AFB carburetor]]s.<ref>{{cite web|url=http://www.automobile-catalog.com/car/1969/635900/dodge_charger_rt_426_v-8_hemi_4-speed_super_track_pack.html|website=automobile-catalog.com|title=1969 Dodge Charger R/T 426 V-8 Hemi 4-speed Super Track Pak|access-date=June 24, 2018}}</ref> In actual [[dynamometer]] testing, it produced {{convert|433.5|hp|kW PS|0|abbr=on}} and {{convert|472|lbft|Nm|abbr=on}} of torque in purely stock form.{{cn|date=March 2023}} Chrysler's sales literature<ref>{{cite web|url= http://www.romocoinc.com/1971-plymouth-rapid-transit-system.htm |archive-url= https://archive.today/20150118064916/http://www.romocoinc.com/1971-plymouth-rapid-transit-system.htm |url-status= dead |archive-date= January 18, 2015 |title=1971 plymouth rapid transit system brochure |publisher=stockmopar.com }}</ref> published both the gross {{convert|425|hp|kW PS|0|abbr=on}} and net {{convert|350|hp|kW PS|0|abbr=on}} ratings for 1971.
[[File:1966 Dodge Charger 426 Hemi engine.JPG|thumb|426 Hemi engine in a 1966 Charger]]
{{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 Hemiversion, including but not limited to [[compression ratio]], camshaft, [[intake manifold]], [[exhaust manifold]]. Some 1960s NASCAR and NHRA Hemi engines featured magnesium [[Ram-air intake|cross-ram intake manifolds]] and magnesium [[oil pan]]s in an attempt to reduce the massive weight of the overall engine, along with chain-driven internal [[dry sump]] [[Motor oil|oil systems]]. Today, aftermarket blocks, heads, intakes, rods, and [[piston]]s are usually made of aluminum.{{cn|date=May 2024}}
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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