The Story Of The Hemi Engine

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By Dave Ashton

Ask any Mopar fan what’s the best engine and unusually the reply will be a Hemi. The hemispherical cylinder head engine has its roots in WWII fighter aircraft in the Republic P-47 Thunderbolt, which was re-engineered at first under the name ‘FirePower’ for Chrysler car engines for the 1951 model year. Desoto vehicles had their own called the Fire Dome, while Dodge went with the name Red Ram.

The hemispherical cylinder head design gave a very efficient combustion chamber and featured two valves per cylinder in a crossflow design, a domed piston and the spark plug near the centre of the combustion chamber.

The original 1951 Chrysler Hemi had 331ci. (5.4 L) producing 180 bhp. Not a mind blowing amount of power, but the potential for the engine design was there and over its three generations, the powerplant has woven itself into muscle car history. It was the second generation Hemi started in 1964 that really cemented its name. Huge size, huge power with aq 426ci. displacement was originally put into a Plymouth Belvedere to see how it fared in NASCAR. To compete in NASCAR they had to have a street version of the Hemi, which had 425 bhp. From here the engine’s reputation continued to grow and now original classic vehicles from that era with a 426 Hemi engine can reach the millions.

The two videos below give you a quick overview of the Hemi’s history, with the second giving a rundown of how the engine works, explained in the unique style only available from Engineering Explained. Although todays 5.7L and 6.2L Hemi engine designs are a far departure from the original with far better efficiency in fuel economy and having variable valve timing and coil on plug distributorless ignition amoungst other features.

The Hemi name is still the calling card for ultimate power when it comes to a Mopar and looks like it will continue it’s reign as shown in the recent Dodge Demon with its 840 horsepower rating. With such a long history and so many variations, the third video below will give you an idea of how one version of the Hemi compares to another, basically old versus new.

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