Who Invented the HEMI Engine?

by Rob Wagner
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Chrysler Corporation, General Motors

The HEMI engine's long and varied history has led to confusion of the identity of its inventor. No single person has earned the distinction as creator. But the engineering feat began with the Welch Motor Car Company in 1904, and the concept has been massaged over the decades until perfected by the Chrysler Corporation.


Alan R. Welch and his brothers, owners of the Welch Motor Car Company, are credited for pioneering the hemispherical engine. The power plant was a simple 20-horsepower, 2-cylinder engine with a single overhead camshaft. Although the General Motors discontinued the HEMI in 1910 when it bought Welch, Peugeot developed its own hemispherical engine. BMW mass-produced a HEMI version before Chrysler engineered it for modern use.


The Welch design served as a blueprint for high-performance engines that were used in military aircraft during World War II and today in dragsters, racing stock cars and high-performance automobiles.


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The HEMI's bowl-shaped combustion chambers, angled valves and twin spark plugs per cylinder allow for greater air intake that gives a more efficient mix of fuel and air to create higher compression and resulting in more power.


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Aside from automotive uses, Pratt and Whitney used HEMI heads on its radial aircraft engines during World War II, while Chrysler used HEMIs in 1939 for its V-16 engines for military aircraft.


The HEMI achieved its greatest success with the 426-cubic-inch model that had a compression ratio of 10.25-to-1 to generate 490 foot-pounds of torque.


The 1904-09 Welch Model 4-0 Tourer models all sported the HEMI engine, while 1966-78 and 2007 Dodge Chargers were heavily marketed by Chrysler as HEMI-powered.


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Zora Arkus-Duntov, who designed a HEMI head conversion for the Ford flathead V-8, is often credited for inventing the HEMI, but the Welch brothers pioneered the engine at least 30 years before his involvement.

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