Polished and chromed 426 Hemi engine in a 1971 Hemi 'Cuda

A Chrysler Hemi engine is one of three different internal combustion engine families from the Chrysler Corporation (or its successor, DaimlerChrysler) that are Hemi engines; in other words, they utilise a hemispherical combustion chamber. A hemispherical cylinder head allows the valves to be inline rather than side-by-side, which gives a straighter, simpler airflow path, allows large valves, and gives greater efficiency. The hemi design places the sparkplug in the center, giving more even ignition.

The advantages of the hemi cylinder head come at the disadvantage of requiring intake and exhaust valve stems that point in different directions, requiring much more complicated rocker arm setups in overhead valve engines. These also increase the space taken up by the cylinder head; Hemi engines are not space-efficient.

The three generations of Chrysler hemi engines included the first (the Chrysler FirePower engine) in the 1950s, the second from the mid 1960s through the mid 1970s, and finally in the early 2000s.

Chrysler developed their first experimental Hemi for use in the P-47 aircraft. This engine, the XP-47H (X for experimental) was a V-16 rated at 2500hp. However, Chrysler has always been known for underrating their engines and the actual performance of this incredible prototype, which survives and is on display at the Walter P. Chrysler Museum, suggests that it actually produced between 3,000 and 3,500 horsepower. It was capable of pulling the P-47, which ordinarily possessed a 2,300hp engine and topped out at 439 mph, to the incredible speed of 504 mph at an altitude of 15,000 feet, which is still an incredible feat for a piston engine. Unfortunately, the engine never saw mass production and the project was cancelled at the end of WWII.

In addition to the aircraft engine, Chrysler developed an experimental V-12 Hemi tank engine as well. Although that particular engine does not seem to have been produced, it seems that Chrysler did apply hemi heads to some of their production tank engines. Jay Leno made it into the news in 2004 by building a hot rod using a Chrysler hemi-headed Patton tank engine producing 810 hp and 1560 lb-ft of torque.

Using their experience with the hemispherical combustion chamber in aero-engines, Chrysler decided to use this layout in their first OHV V8 in 1951, introducing a 180 hp (134 kW) Hemi V-8 with a displacement of 331 in³ (5.4 L). Starting in 1951, Briggs Cunningham chose to use the Hemi, and in 1953 the Hemi powered Cunningham C5-R won first in his class, and his cars finished as high as third place overall at the 24 hours of Le Mans. Chrysler abandoned the hemispherical concept in 1959 in favor of the wedge-head Chrysler B engine.

The hemispherical head design was revived in 1964. These were the first engines to officially use the "Hemi" name, a word Chrysler trademarked. All Chrysler Hemi engines of the 1960s displaced 426 in³ (7.0 L). Although just 11,000 Hemi engines were produced for consumer sale, the engine became legendary, with "Hemi" becoming one of the most familiar automobile-related words in the United States. The 426 Hemi was nicknamed the "elephant engine" at the time, a reference to its far-from-compact dimensions and extraordinary power.

Hemi Head	Typical Head

The first 426 Hemi of the 1960s was the NASCAR race engine, introduced in 1964. It earned recognition when it placed first, second, and third in the 1964 Daytona 500 race. This famous engine was sized for NASCAR (which mandated engines under 428 in³/7.0 L) with an oversquare 4.25 in (107.9 mm) bore and 3.75 in (95.2 mm) stroke like the Chrysler RB engine big-block. The engine's success led the series organizers to effectively legislate the racing Hemi off the track.

The 426 Hemi was produced for consumer automobiles from 1965 through 1971, and new crate engines and parts are available today from DaimlerChrysler Corporation. There were many differences between the Hemi and the Wedge-head big-block, including cross-bolting and a different head bolt pattern. The street Hemi version was rated at a very conservative 425 hp (317 kW) with two Carter AFB carburetors. In reality, the engine could produce 450 to 475 hp (336 to 354 kW) and 490 ft .lb of torque.

This engine was used in the following vehicles:

1965–1970 — Dodge Coronet/Plymouth Belvedere 426-S
1965–1971 — Plymouth Satellite
1966–1971 — Plymouth GTX
1966–1971 — Dodge Charger
1968 — Dodge Dart
1968 — Plymouth Barracuda
1968–1971 — Dodge Super Bee
1968–1971 — Plymouth Roadrunner
1968–1971 — Plymouth 'Cuda
1969 — Dodge Daytona
1970 — Plymouth Super Bird
1970–1971 — Dodge Challenger

Modern Hemi

The modern Hemi is not really a hemi at all - it has a polyspherical combustion chamber similar to that in many other modern engines. A true hemi head was considered in the design phase, but it was rejected and only the near-perpendicular valve arrangement remains. The Hemi replaced Chrysler's large LA family of engines, particularly the Magnum 5.9, in the early 2000s.

Hemi 5.7

Photo courtesy DaimlerChrysler 5.7-liter HEMI Magnum V-8 engine

The 5.7 liters, was released in 2002 on the Dodge Ram 2500 and 3500 pickup trucks to replace the Magnum 5.9 engine. The buying public was enthusiastic about the engine, and snapped up Rams and Hemi-powered Dodge Durangos at an amazing rate. Chrysler reacted by putting the 5.7 liter Hemi in the 2003 Dodge Ram 1500, 2005 Chrysler 300C and Dodge Magnum, and the 2005 Jeep Grand Cherokee.

The 5.7 Hemi in the Ram delivered 345 hp (257 kW) and 375 ft.lbf (508 Nm), but 340 hp (254 kW) and 390 ft.lbf (529 Nm) for the 300C and Magnum. It is a 90-degree V8, 2-valve pushrod design displacing 5654 cc (345 in³), with a bore of 99.5 mm (3.92 in) and a stroke of 90.9 mm (3.58 in). The block appears to be based on the Chrysler LA engine as it has the same stroke.

A new displacement on demand technology called Multi-Displacement System (MDS) is used in some versions which can shut off a bank of cylinders under light load to improve fuel economy.

The 5.7 liter Hemi is made at Chrysler's Ramos Arizpe, Mexico Saltillo Engine plant, and the truck is assembled in Saltillo Truck Assembly plant.

The Hemi was on the Ward's 10 Best Engines list for 2003 through 2006.

This engine is used in the following vehicles:

2003-05 Dodge Ram
2004-05 Dodge Durango
2005 Chrysler 300C
2005 Dodge Magnum
2006 Dodge Charger
2005 Jeep Grand Cherokee

Photo courtesy Daimler Chrysler 5.7-liter HEMI Magnum V-8 engine from the 2003 Dodge Ram

Hemi 6.1

Chrysler has developed another modern Hemi, this time at 6.1 liters to replace the Ram Tough V10. The engine is bored-out to 103 mm (4.1 in), but many other changes were made to allow it to produce 425 hp (317 kW) at 6200 RPM and 420 ft.lbf (569 Nm) at 4800 RPM. The engine block is different, with revised coolant channels and oil jets to cool the pistons. A forged crankshaft, lighter pistons, and strengthened connecting rods add durability. A new cast aluminum intake manifold is tuned for high-RPM power and does not include variable-length technology. Chrysler's Multi-Displacement System is not used.

Applications:

2005 Chrysler 300 SRT-8
2005 Dodge Magnum SRT-8
2006 Dodge Charger SRT-8
2006 Jeep Grand Cherokee SRT-8 (415 hp/310 kW)

Hemi 6.4

Chrysler unveiled a monster 6.4 liter engine at the 2005 SEMA auto show. This engine puts out 505 peak horsepower and will be available as a crate engine. There are no official plans to use it in a production car. If it is used in a production car in the future, it might need modifications in order to meet production requirements.

The term, "Hemi engine", is a trademark of Chrysler Corporation, although the concept is used by many manufacturers.