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History of the Hemi V-8 Engine

From Then to Now

Alex Steele
Jun 5, 2017
Contributors: ASE Master Technician
Most everybody’s seen the “HEMI” logo on recent Chrysler-produced cars and trucks. Many muscle-car fans picture a 426ci big-block whenever the subject comes up in conversation. But still there are a few history buffs familiar with the origination of Chrysler’s “hemispherical combustion chamber” coming out of WWII, or even back to the early 1900s where the design actually began.
Photo 2/9   |   History Hemi V8 Engine Piston
The basis of the hemi design is fairly simple. The shape of the cylinder head’s combustion chamber is approximately half of a sphere—picture a grapefruit cut down the middle and hollowed out. This allows the spark plug to be placed top-center, which shortens the burn distance of the air/fuel mixture. At the same time, on overhead-valve engines, a large intake and exhaust valve is fitted on either side of the plug to enhance intake air and exhaust flow in and out of the combustion chamber. Due to the hemisphere shape, flattop pistons could not produce sufficient compression, so domed pistons were used to make up the difference.
Even at its most basic stages of development, the hemispherical configuration proved to augment the combustion process and increase engine power.
Photo 3/9   |   History Hemi V8 Engine

Earliest Hemis

The hemi design actually came into existence with some of the earliest automotive internal combustion engines. Belgian carmaker Pipe produced a four-cylinder hemi in 1905, and the Fiat 130 HP Grand Prix race car brought it to the track by 1907. Several manufacturers followed suit with the more powerful combustion-chamber technology through the coming decade.

Chrysler Hemis

Overall hemi-style, combustion-chamber production dropped off due to cost issues subsequent to the power rush of the originals, but Chrysler prompted a rebirth following World War II.
Chrysler engineers committed themselves to the testing and development of Hemi engines throughout the war for military and aeronautic use. There were two experimental models completed. One was the V-12 AV-1790-5B engine used in the M47 Patton tank. The other was the massive XIV-2220 (a 2,220ci V-16) to power a P-47 Republic Thunderbolt fighter aircraft. The XIV-2220 was rated at 2,500 hp and surpassed 500 mph on test flights. Although the project was considered a success, the end of the war and oncoming of jet aircraft technology eliminated demand, and the V-16 never made it into production.

First Generation Hemi (1951-1958)

Hemi knowledge gained during and post-WWII hit the street in 1951 with the production of Chrysler’s first overhead-valve V-8, replacing the flat head (which had its valves in the cylinder block). The cast-iron, 331ci “FirePower” engine was rated at 180 hp.
Some of Chrysler’s divisions created their own dissimilar inline-six and V-8 Hemi versions, although Plymouth did not incorporate a first-generation Hemi into its lineup.
Chrysler and Imperial: FirePower (331, 354, 392 ci)
Desoto: Fire Dome (276, 291, 330, 341, 345 ci)
Dodge: Red Ram (241, 270, 315, 325 ci), Power Giant (354 ci), intended for heavy trucks.

Second Generation (1964-1971): The 426

From a baby-boomer perspective, the 426 is the definition of a Hemi. After a stall in production following the first generation, Chrysler produced what some called the “Elephant Engine.” This was the first hemispherical head design engine to wear the trademark HEMI name.
Photo 4/9   |   History Hemi V8 Engine 426
The 426ci extra big-block was originally built for NASCAR racing inside the ’64 Plymouth Belvedere. The new breed of Hemi swept the top three spots at the Daytona 500. But the Hemi was banned by new regulations in 1965 due to Chrysler’s lack of Hemi street sales and complaints from competitors of an unfair power advantage. Some Dodge Dart, Coronet, and Plymouth Fury models were sold to the public with the race version of the 426, but significant production of milder street configured engines didn’t begin until 1966. This permitted Hemi-equipped stock cars a return to the NASCAR circuit.
The street Hemi was toned down with a lower compression ratio (10.25:1, compared to the race engine’s 12.5:1), replacement camshaft, milder intake and exhaust manifolds, and possibly more. But still put out a respectable 425 hp.

Street Hemi Models

Dodge
Challenger (1970-1971)
Charger (1966-1971)
Charger Daytona (1969)
Coronet (1966-1970)
Dart SS (1968)
Super Bee (1968-1971)
Plymouth
Barracuda/’Cuda (1970-1971)
Barracuda SS (1968)
Belvedere (1966-1970)
Fury GT (1970)
GTX (1967-1971)
Road Runner (1968-1971)
Satellite (1966-1971)
Superbird (1970)
Monteverdi
Hai 450 (1970)
The 426 HEMI is a muscle-car legend, and for good reason. Hemi-equipped street-car sales ended at the ’71 model year, but the race-car industry caught the drift. The NHRA Top Fuel class features the most powerful race cars in the world, with engine’s pumping out 11,000 hp at the crankshaft. These carbon-fiber-bodied dragsters and Funny Cars exceed 300 mph in less than 4 seconds over a span of 1,000 feet.
Here’s what a lot of folks believe is the most impressive facet of the Elephant Engine’s history. These 500ci, nitromethane-burning monsters are aluminum, modified, supercharged replicas of Chrysler’s second-generation 426 HEMI—maintaining basically the same hemispherical-style, two-valve combustion chamber cylinder heads.
Classic Hemi muscle cars are at the top of a few collectors’ to-do lists. Chrysler sold just 16,159 Plymouth Barracudas for the ’71 model year; 119 were the famed Hemi ’Cuda, 11 of which were convertibles. Only two of those convertibles were equipped with a four-speed transmission. One of those two manual-transmission, Hemi-powered Plymouth convertibles sold at auction in 2014 for $3.5 million.

Third Generation (2003-present)

Chrysler’s first- and second-generation Hemis went, for the most part, to racers and high-end performance car buyers. But the third generation maintains the basic Hemi philosophy and produces exceptional power, but this time, anybody can drive one.

5.7L Hemi

Dodge released the 5.7L V-8 Hemi engine with the ’03 Ram 1500, 2500, and 3500. The modern combustion chamber was modified with a near-perfect hemisphere, two spark plugs (akin to drag-race versions), and current technology in spark advance and fuel injection, which improved efficiency significantly compared to the second generation.
Photo 5/9   |   History Hemi V8 Engine 5.7L
The 5.7L was updated for ’09 with variable valve timing, modified cylinder heads and intake manifolds to increase airflow, and an available variable-displacement system. Depending on model, horsepower ranged from mid- to high-300s, and the Hemi was available in cars and trucks from each of Chrysler’s brands.
Chrysler
300C (2005-present)
Aspen (2007-2009
Dodge
Challenger (2009-present)
Charger (2005-present)
Durango (2004-2009, 2011-present)
Magnum (2005-2008)
Jeep
Commander (2006-2010)
Grand Cherokee (2005-present)
Ram
Pickup (2003-present)

6.1L Hemi

Beginning in ’05, a 6.1L Hemi was available, courtesy of Chrysler’s Street and Racing Technology division. SRT produced sportier models of the Chrysler 300C; Dodge Challenger, Charger, and Magnum; and the Jeep Grand Cherokee. Power was boosted to 425 hp and 420 lb-ft of torque in these SRT8 versions, with help from an improved engine block, lightweight pistons, and modified intake manifold.

6.4L/392CI Apache

Using the 392ci logo (392 Hemi) to connect with the largest first-generation engine and sold only individually in-crate, this new design became available in 2007 with 525 hp and 510 lb-ft.
Photo 6/9   |   History Hemi V8 Engine 392
The production version of the 392 Hemi (or 6.4 Hemi, model-specific), codenamed Apache, is based significantly on the 5.7L (codenamed Eagle) with street horsepower in the high-400s. The new Hemi was released in the ’11 Dodge Challenger SRT, and since then, it’s been made available in the Dodge Charger, Chrysler 300, and Jeep Grand Cherokee.
A 6.4L, specifically tuned for work with increased fuel economy and improved towing force, became available in the ’14 Ram Heavy Duty. It currently sees use in a variety of Ram models, including the rugged Power Wagon.
Photo 7/9   |   History Hemi V8 Engine 6.4L

6.2L Hellcat

For ’15, Chrysler got a bit aggressive with the third-generation Hemi and produced the all-new 6.2L Hellcat, available onboard the Dodge Challenger and Charger. Rated at 707 hp and 650 lb-ft, this supercharged beast is currently the most powerful series-production engine in history (excluding exotic limited-production mills from the likes of Bugatti and Pagani). It includes variable valve timing, but Chrysler engineers left out variable displacement. The name pays tribute to Grumman’s F6F Hellcat fighter aircraft, which had a dominant role in the Pacific during World War II.
Photo 8/9   |   History Hemi V8 Engine 604
Photo 9/9   |   History Hemi V8 Engine 572

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