This bad boy has a HEMI in it !

by Christopher Jensen  

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How many times have you heard that phrase thrown around? You may have heard the commercials, even remember or heard of the legendary Chrysler HEMI engines of the 1950s, '60s and '70s, but do you know what makes a Hemi engine, well, a Hemi? Chrysler's marketing campaign has helped to revive the awe of the Hemi engine and has helped to associate the term Hemi with big, powerful engines.

The Hemi engine was introduced by Chrysler in 1951 in a new line of V8 engines called the "Hemi."  The name Hemi came from the shape of the cylinder heads, which had a hemispherical design to the cylinder head's combustion chamber.  While not a new design for the time, it was a first for passenger cars.  Most cars prior to the 1950s used what was known as a flat head where the valves are in the block, rather than in the head, and open in a chamber beside the piston. This very simple "Flat Head" design is still in use today but mainly in smaller, cheaper engines such as lawnmowers.

The Hemi engine is different from the standard V8 engines in three main ways:

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First the combustion chambers are hemispherical in shape, which creates better thermal and volumetric efficiency. Thus, the engine can create more power without increasing compression This in turn requires a higher octane fuel.
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Second, the valve placement within the combustion chamber are directly across from each other, as opposed to side-by-side. This allows for better flow of the intake and exhaust gases.
    

Third, the spark plugs are better positioned within the chamber to provide maximum ignition combustion.