The Hemi: When, What and Why
was the dominant force in European sports car racing, with its hemi-powered 328 series. In 1948 Jaguar introduced its famous XK engine, complete with hemi heads, not to mention double overhead cams (in street sedans, no less). In 1950 Chrysler completed work on the engine that revised American high performance standards, and introduced the hemi in 1951 models. First offered in Chrysler and then DeSoto models, hemis didn't make it into the Dodge lineup until 1953. But by 1955 it had developed into the Super Red Ram 270. Chrysler was actually selling DeSoto "FireDome" hemi engines to the French luxury carmaker, Facel Vega, beginning in 1954. (Does anyone remember William Holden's DeSoto hemi-powered Facel Vega in the original Sabrina?)
The company introduced the famous Chrysler 300 in 1955. Its hemi engine produced a then phenomenal 300bhp, and sported two four barrel carburetors, a full race cam, solid lifters, and enlarged valves.
Not that the early Chrysler hemi engines will likely be forgotten, but the one that stole the show for keeps, and the one few Americans of the era are going to forget, is the 426 Hemi. Chrysler had developed a racing version in the early 1960's, and introduced the street version in 1966. From then through 1971 Dodge and Plymouth models housed the famous engine.
And the parade continues. In the early 1960's, Harley-Davidson "discovered" the hemispherical combustion chamber. Ford introduced another hemi in its Escort in 1980. SAAB discovered its hemi in 1983. And Daimler-Chrysler is on the threshold of continuing the tradition with a new generation of Hemi power in the 2006 Dodge Charger. It remains to be seen if the engine will be substantially modified from the 5.7 liter version Daimler-Chrysler has been cranking out since 2002, from their factory in Salitillo, Mexico.
But just what is the hemi concept? And why is it a superior design?
The designation "hemispherical" derives from the fact that a sphere represents the smallest amount of space that can contain a given volume. In an engine, the head covers the tops of the cylinders, and the space over each cylinder is therefore half a sphere, or a hemisphere. The least amount of space also means the least amount of material involved. And minimizing the total surface area results in the least amount of heat retention. The cooler the head stays, the more efficiently the engine makes its power.
Aside from easier heat dissipation, the design also aids
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