Hemi

Hemi is short for hemispherical combustion chamber, a cylinder head design where the roof of each combustion chamber is shaped like half a sphere rather than the flatter wedge shapes used by most engines. This shape allows for larger valves positioned at an angle to each other, which can improve airflow into and out of the cylinder and allow for more efficient combustion at high RPM.

Chrysler introduced its first Hemi V8 in 1951, but the name became legendary with the second-generation 426 Hemi introduced in 1964, a race-bred engine that dominated NASCAR before being detuned for street use in muscle cars like the Dodge Charger and Plymouth Road Runner. The 426 Hemi's reputation for raw power helped define the muscle car era of the 1960s and early 1970s.

Chrysler revived the Hemi name in 2003 with a third-generation engine family used in modern Dodge, Ram, and Jeep vehicles. Despite carrying the Hemi branding, these modern engines use a more conventional, less-than-fully-hemispherical chamber shape for practical reasons like emissions and cost, though they retain the name as a nod to the original design's performance legacy.