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Chrysler Hemi

426
1971 Plymouth Hemi 'Cuda engine.jpg
Polished and chromed 426 Hemi engine in a 1971 Hemi 'Cuda
Overview
Manufacturer Chrysler
Also called Elephant engine
Production 1964–1971
Combustion chamber
Configuration V8
Displacement 426 cu in (7.0 l)
Cylinder bore 4.25 in (107.95 mm)
Piston stroke 3.75 in (95.25 mm)
Cylinder block alloy Cast iron
Cylinder head alloy
Valvetrain OHV
Compression ratio 10.25:1
Combustion
Fuel system Carburetor
Fuel type Gasoline
Oil system
Cooling system Water-cooled
Output
Power output
  • 425 bhp (317 kW) (Gross)
  • 350 bhp (261 kW) (Net)
Torque output 490 lb·ft (664 N·m)
Chronology
Predecessor 426 Wedge
Third Generation Chrysler Hemi
Overview
Manufacturer Chrysler
Production 2003-present
Combustion chamber
Configuration V8
Displacement
  • 5,654 cc (345 cu in)
  • 6,058 cc (369.7 cu in)
  • 6,166 cc (376.3 cu in)
  • 6,407 cc (391 cu in)
Cylinder bore
  • 99.49 mm (3.917 in)
  • 103.00 mm (4.055 in)
  • 103.89 mm (4.090 in)
Piston stroke
  • 90.88 mm (3.578 in)
  • 94.59 mm (3.724 in)
Cylinder block alloy Cast iron
Cylinder head alloy Aluminum
Valvetrain OHV
Compression ratio
  • 9.5:1
  • 9.6:1
  • 10.3:1
  • 10.9:1
Combustion
Fuel system Sequential multiport fuel injection
Fuel type Gasoline
Oil system Wet sump
Cooling system Water-cooled
Chronology
Predecessor

The Chrysler Hemi engines, known by the trademark Hemi, are a series of I6 and V8 engines built by Chrysler with hemispherical combustion chambers. Three different types of Hemi engines have been built by Chrysler for automobiles: the first (known as the Chrysler FirePower engine) from 1951 to 1958, the second from 1964 to 1971, and the third beginning in 2003. Although Chrysler is most identified with the use of "Hemi" as a marketing term, many other auto manufacturers have incorporated similar designs.

During the 1970s and 1980s, Chrysler also used the Hemi name for their Australian-made Hemi-6 Engine and applied it to the 4-cylinder Mitsubishi 2.6L engine installed in various North American market vehicles.

A hemispherical cylinder head ("hemi-head") gives an efficient combustion chamber with an excellent surface-to-volume ratio, with minimal heat loss to the head, and allows for two large valves. However, a hemi-head 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 "cross-flow" head design. Since 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 desired compression ratio the piston crown is domed to protrude into the head at top dead center, resulting in a combustion chamber in the shape of the thick peel of half an orange.

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 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.


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