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There are few more evocative four-letter words in the world of motoring than Hemi.
Its derivation may be plain, and of little interest to non-engineers, but in just two syllables it conjures up thoughts of muscle cars with huge power, thunderous noise and huge acceleration.
You might think that all Hemi V8s were part of the same family, but in fact Chrysler has built them in three widely-spaced generations, and the name wasn’t even used for the first, though it reasonably could have been. Still, they all share the same spirit, which is as good a reason as any to look at them all in one go.
Please note: power figures for pre-1972 cars are quoted, as they were in period, in gross horsepower, when the power was measured without accessories fitted. The figures are therefore substantially higher than they would be using modern measurements.
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Background
A hemi engine is simply one with a hemispherical combustion chamber. If you don’t know what that is, it’s not important. What matters is that although it has certain disadvantages (you can’t have more than two valves per cylinder, for example) it produces an awful lot of power.
Chrysler was nowhere near the first manufacturer to use the design, but learned a lot about it while developing the V16 XIV-2220 aircraft engine during World War Two, destined for the P-47 Thunderbolt fighter. However, the end of the war and the arrival of the jet age pre-empted production, it has its place in history as the company’s first hemi. PICTURE: Second-generation Hemi 426
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FirePower 331
The first Chrysler engine described retrospectively as a hemi – and indeed the company’s first V8 - was the FirePower, fitted initially in 331 cubic inch (5.4-litre) form to the 1951 model year Imperial, New Yorker and Saratoga (pictured). Power outputs started at 180hp and would soon rise to 250hp.
The 331 also powered Chrysler’s phenomenally noisy cold war era Victory air raid siren, which is said to be audible from over 30 miles away in suitable weather conditions.
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FirePower 354
The 331 was replaced in 1956 by the 5.8-litre 354, which had the same stroke but a larger bore. It was fitted to several Chryslers in 280hp form, but for the 300 series it was uprated to 340hp, with a high-compression 355hp unit available as an even more interesting option.
With this last version, Chrysler had achieved one horsepower per cubic inch, the equivalent of around 61bhp/litre today – a very impressive figure for a road-going engine of the mid 1950s.
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FirePower 392
The largest first-generation Hemi, introduced in 1957, had increased bore and – for the only time – stroke dimensions, giving a capacity of 392ci (6.4 litres). Its lowest official power output was 325hp, but in the 300 series it was available with up to 380hp on carburettors.
An even more potent 390hp version with fuel injection was built in very small numbers, but the system was unreliable.
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Dragsters
By 1960, extremely highly modified, nitro-fuelled versions of the 392 had become very popular in drag racing. Among the fastest cars was Swamp Rat III, built by one of the sport’s greatest exponents, Don ‘Big Daddy’ Garlits (born 1932).
Garlits was sponsored for a time by Chrysler’s Dodge division. The fact that Dodge used the Hemi engine in its cars and trucks – where it was branded Super Red Ram and PowerDome respectively – justified the claim that Swamp Rat was ‘Dodge powered’.
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DeSoto
Starting in 1952, Chrysler’s DeSoto brand used several versions of the Hemi in its final decade. These were generally smaller than the Chrysler units, starting at a relatively modest 276ci (4.5 litres).
The largest were the 341 and 345ci (both 5.6 litres) units of 343hp and 345hp which respectively powered the 1956 (pictured) and 1957 model year DeSoto Adventurer.
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Facel Vega
French manufacturer Facel Vega used early Hemis for most of its luxury cars. The first ten examples of the Excellence (pictured) were fitted with the 392 in 1958, but this was the last year of the engine, and when stocks dried up Facel Vega switched to its replacement, the B-Series, which had a wedge-shaped combustion chamber and was therefore in no sense a hemi.
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The ‘real’ Hemi
The second-generation Hemi, and the first to be called that officially (though it also became known as the Elephant), was created specifically to bring Chrysler success in NASCAR racing. It consisted of a 426ci (7.0-litre) RB engine – a B-Series with a taller block – whose ‘wedge head’ was replaced by one of the older and more complex hemi design.
It first appeared at the 1964 Daytona 500, where drivers of modified Plymouth Belvederes took the first three places. The winner, Richard Petty (born 1937), went on to become that year’s NASCAR champion.
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426 Street version
NASCAR quickly banned the 426 Hemi by creating a rule demanding that race engines had to be based on ones available in road cars. Chrysler responded by developing the Street Hemi, a toned-down version which, in its short but memorable production life from 1966 to 1971, was never quoted as having producing anything other than a possibly understated 425hp.
The street cars allowed Chrysler brands to return to the NASCAR tracks from the 1966 season.
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Winged Warriors
In 1969 and 1970, Dodge, Ford, Mercury and Plymouth competed in NASCAR in cars known as the Aero Warriors because their front ends had been radically restyled to improve aerodynamic efficiency. The Dodge Charger Daytona (pictured) and Plymouth Superbird twins formed a subset called the Winged Warriors due to their enormous rear wings, which extended above roof level. Both were powered by the 426 Hemi.
NASCAR found a way to eliminate these cars – which, though dramatic, bore little resemblance to mainstream road vehicles – from its events, but not before Bobby Isaac (1932-1977) won the 1970 series in a Superbird.
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Monteverdi
The Hai 450 SS was a supercar built by Swiss manufacturer Monteverdi and unveiled at the 1970 Geneva motor show. It was powered by a 426 Hemi mounted between the seats and the rear wheels.
The Hai seems to have been intended as a production car, but sources say only four were ever built, two in the early 1970s and the others 20 years later.
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End of the Elephant
The 426 remained available as an option in cars such as the Dodge Super Bee only until 1971. Total production of Hemi-engined cars in this era has been reported to be 10,904.
For maximum power from a Chrysler vehicle thereafter customers could choose the RB engine, available in sizes up to 440ci (7.4 litres) though never producing as much power as the Hemi did, until it was discontinued in 1978.
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More dragsters
Even more than the Firepower 392, the 426 caught the imagination of the drag community in a big way. Even today, nearly half a century after it went out of production, its basic design is still the template for supercharged, nitromethane-fuelled Top Fuel and Funny Car dragsters, though every component is nowadays built by specialist companies.
Measuring their power output is not easy, but a 2015 attempt gave a spike reading of unworldly 11,051bhp. If one of these cars accelerated from 0-300mph in four seconds at a professional meeting, it would be considered hopelessly slow and would require a lot of work to make it competitive.
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Customer dragsters
Although dragsters are usually built by amateur enthusiasts or professional teams, lightened Plymouth Barracudas and Dodge Darts were sold in 1968 specifically for drag racing. The cars were much lighter than standard, had race-spec engines and were not street legal.
They have proved to be remarkably durable. Gary Wolkwitz’s Dart is pictured here at the 2017 Mopar HEMI Challenge, nearly half a century after it was built.
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Return of the Hemi
Chrysler trademarked the HEMI name (now in all capital letters) and used it for a third generation even though these engines did not have completely hemispherical combustion chambers.
In its original form the new design, relatively moderately sized at 5.7 litres and producing around 340bhp depending on model, first appeared in Dodge Ram trucks in the 2003 model year. Ward’s AutoWorld magazine gave it a place in its annual top ten of engines available in the US six times from that year to 2009.
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Cylinder deactivation
From 2009, some versions of the 5.7 were given a form of cylinder deactivation which Chrysler called the Multi-Displacement System. With this, the HEMI would run on four cylinders rather than the full eight when only small amounts of power were required, in the interests of fuel economy. The basic principle dated back to 1908 but – after a brief and largely disastrous experiment by GM with the 1981 Cadillac model year – the tech had only recently started to make a comeback.
Other developments at this time included revised cylinder heads and the introduction of variable valve timing.
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SRT-8
SRT-8 versions of the Chrysler 300C (or 300 as it was known in North America), Dodge Challenger, Dodge Charger, Dodge Magnum and Jeep Grand Cherokee (pictured) were introduced from 2005.
All had an uprated version of the HEMI which, among other changes, was enlarged to 6.1 litres. Power output in most applications was 425bhp, well above the highest amount available in the 5.7.
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6.4 Apache
Although a new aluminium-block 7.0-litre 426 HEMI was unveiled at the Detroit Show in 2012, the largest new-generation engine in production cars is the 6.4-litre Apache.
Available in SRT-8 models (since renamed SRT) such as the Dodge Charger pictured here, it produced 470bhp on its launch in 2011 but was uprated to 485bhp for the 2015 model year.
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Hellcat
At 6.2 litres, the Hellcat version of the HEMI engine is slightly smaller than the Apache, but thanks to a supercharger and several other modifications it is much more powerful, with an official output of 707bhp.
It’s offered in the Dodge Challenger and Charger, and in the Jeep Grand Cherokee (where it’s known as the Trackhawk) and as a crate engine called, reasonably enough, the Hellcrate. The Challenger Hellcat Redeye is even more powerful, producing up to 797bhp.
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Demon
Unimaginable as it would have seemed back in the days of the Firepower 331, the HEMI broke the 800bhp barrier in 2018, when a Dodge Challenger fitted with the new Demon engine was launched. With a larger supercharger than the Hellcat, it produces a maximum of 808bhp on pump petrol, rising to 840bhp if you use 100-octane racing fuel.
The official 0-60mph time is 2.1 seconds, and it is one of the very few standard production cars to have been timed in a standing-start quarter-mile acceleration test at under ten seconds. The Hemi story is far from over...
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