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What Is A Hemi Engine?
The Hemi engine gets its name from the overhead valve hemispherical combustion chambers to facilitate the burning of the fuel/air mix more efficiently. The domed shape of the heads allows the top of the piston to shorten the combustion space, improving the efficiency of the burn and creating better performance (more power) from the engine. This arrangement allows larger valves to be located on opposite sides of the chamber with a spark plug located at near dead center. The result is a robust energy exchange that the motor can use to propel the vehicle's drivetrain.
The History Of The Hemi Engine
Many believe that Chrysler invented the Hemi engine, but the design was developed long before the American car company became involved. The earliest version of the hemispherical engine was used in Pipe (Belgian automaker) in 1905. Over the years, several other companies, including Fiat, Peugeot, Alfa Romeo, and others experimented with the engine design with varying degrees of success. However, the engine was considered too expensive to produce, so it was discontinued until the end of WWII.
Chrysler's first involvement with the hemispherical engine occurred toward the end of the Second World War when it developed an experimental engine for military aircraft. Even though the engine was well-received, the war was winding down, so the motor was never produced, Chrysler used the lessons they learned to develop the first Hemi engine for use in their vehicles a few short years later.
The First Generation: FirePower
Chrysler introduced their version of the hemispherical engine in 1950, which they dubbed the “Firepower.” The initial engine displaced 331 cubic inches (5.4L), producing 180 hp. Chrysler quickly touted the engine as the most powerful and efficient V8 ever built and armed their salesmen with special bulletins, claiming that their test engines showed “less wear, less power loss, and less deterioration than other competitive engines.”
The Hemi engine design was so well-received that three of the four Chrysler divisions were soon formulating their own Hemi engines with different displacements and power outputs before. At that time, there was no universal sharing of engine components between sister companies, so the engines shared almost no similar parts.
During the fifties, the Hemi engine continued to grow in various sizes and displacements. Chrysler was quick to take advantage of the impact that it could have on racing applications (not to mention the free advertising in what was becoming an increasingly popular sport). The Chrysler Firepower engines became known in the European Le Mans, NASCAR races, and on the drag strip. As the first engine to produce over 300 hp, the Hemi dominated the track, powering Chrysler and Dodge to several victories. In 1955, a Hemi engine powered the Chrysler 300C to 27 victories, giving Chrylser the Constructor Championship for that year.
Toward the end of the fifties, each of the three Chrysler divisions were using the engine in most of their vehicles. Unfortunately, Chrysler began to feel the pinch of economic conditions and decided that the Hemi was too expensive and began looking at other alternatives. The “B” wedge-style engines provided just as much power and were cheaper to produce, so the decision was made to discontinue production on the Hemi.
The Second Generation: The Mighty 426
The Hemi’s hiatus was short-lived, as it was revived again in 1964 with a displacement of 426 cubic inches. Developed to be used on the racing circuit and first appearing in a Plymouth Belvedere, the engine was not available to the public. The 426, dubbed “the elephant engine,” dominated the track almost as soon as it was used, prompting NASCAR to ban the engine for the 1965 season. (While NASCAR claimed the reason was that the Hemi was not being offered in production vehicles (which were the rules), many historians believe that Ford was so intimidated by the engine that they had a hand in getting the motor banned).
Chrysler corrected the issue by producing and offering a street Hemi motor for many of its vehicles from 1966. The 426 V8 produced 425 hp and 490 lb-ft of torque (when equipped with a 4-bbl carburetor) until 1971 and developed a reputation as a powerful motor when muscle cars were all the rage. Chrysler and Dodge charged extra for the Hemi option, which limited their production (most owners wanted to avoid paying close to a thousand dollars for the motor). In some cases, the number of Hemi-equipped vehicles is relatively low. For example, a 1971 Plymouth ‘Cuda Hemi Convertible with a manual transmission (one of a handful produced) was not sold in 2021 despite a high bid of $4.8 million.
Like its fifties predecessor, the 426 Hemi significantly impacted the race track. A 426 Hemi-equipped Dodge Daytona Charger was the first car to exceed 200 mph when Buddy Baker performed the feat in 1970. Richard Petty won the Daytona 500 seven times, with five victories (1964, ‘66, ‘71, ‘73, and ‘74) being 426 Hemi-powered cars.
The race Hemi engine also found its place in NHRA racing, with many Funny Cars and Super Stock racing teams using the 426 Hemi engine. Famous drivers like Ronnie Sox, Don “The Snake” Prudhomme, and “Big Daddy” Don Garlits were just a few of the racers adapting the engine for their sport.
The Hemi engine was discontinued in 1971. Americans were increasingly moving toward smaller, more fuel-efficient vehicles and abandoning their muscle cars. The automotive industry would move into the “Malaise Era,” emphasizing fuel economy and emissions standards were valued more than pure power.
The Third Generation: The Hemi Comes Roaring Back
In 2003, Dodge released the Gen III Hemi (5.7L) for use in its Dodge Ram trucks, even though the new engine was much different than the earlier Hemispherical engines produced in the 50s and late 60s. With a larger intake and exhaust valves to increase airflow (and a new intake manifold), the new Hemi engine had a coil-on-plug distributor-less ignition system with two spark plugs per cylinder. The new configuration improved power, reduced carbon emissions, and improved fuel economy.
The rebirth of the 5.7 Hemi produced 345 hp and 375 lb-ft and was used first in the 2003 Dodge Pickup. A year later, Chrysler expanded the engine offering to the Dodge Durango along with its Dodge trucks. The motor entered other Chrysler and Jeep vehicles (Jeep Grand Cherokee/Commander). The engine received a revision in 2009, adding VCT and revised intake manifolds.
In 2015, the “Hellcat” Hemi engine debuted to power Dodge’s reborn muscle cars. The engine had a power output 707 hp and 650 lb-ft of torque, which at the time made it the most powerful production engine ever made. In 2018, Dodge upped the ante with the Dodge Demon SRT Redeye and an even more powerful Hemi engine (797 hp). (About the same time, Dodge announced the Hellcats would be sold as crate engines). The 2023 Dodge Challenger SRT Demon 170 can motor down the track in 1.66 seconds, with a top speed of 212 mph, producing over 1,025 hp.
The End Of The Hemi
In 2023, Dodge announced the end of the Hemi engine as the carmaker began to shift to electric-powered vehicles. The “Last Call” Dodge Charger and Dodge Demon Challenger were offered in limited production numbers (3k units) and stopped taking orders in May. While Dodge has not yet released its new Charger EV to the public, they have provided enough information to ensure that the legacy of Mopar performance built over the years will likely continue.
