This year marks the 50th anniversary of one of the world's most iconic names in automotive power: Hemi.

The Hemi engine has changed and revolutionized how people perceived what kind of power an engine can produce under the hood. Like all other things, the Hemi engine had its own humble beginnings before it rose to prominence. So  read on as we take a step back through time to go through the half-century story of the famed Hemi engine.

The name “Hemi” is derived from the word hemisphere, meaning it's an internal combustion engine that has a hemispherical-shaped chamber. The valves of the Hemi engine are positioned at a 58-degree angle that allows airflow to better burn the fuel and air mixture generating a higher power output.

The Hemi engine, like everything else, has its own pros and cons. Starting with the pros, the Hemi engine has a smaller surface area compared to a flat head. With this, less heat escapes from the Hemi engine providing a higher peak pressure. Another advantage of the Hemi engine is its 58-degree valve angle because it gives a straighter flow path for the intake and exhaust to and from the cylinder head. Furthermore, the large valve size of the Hemi engine works to its advantage because it allows an improved engine airflow.

Now we look into the cons. One of the disadvantages of the Hemi engine is the amount of valves it permits on its chamber. With an angled valve, the Hemi only has two. It’s a disadvantage because four valves can make the engine breathe easier. Moving on, the Hemi engine has smaller combustion chambers that further reduces the heat loss and shortens the flame propagation distance during combustion. Lastly, the high relative weight of the Hemi engine contributes to its disadvantage.      

Chrysler is often associated and credited for the development of the Hemi engine, but it was the Chelsea Manufacturing Company of Michigan who manufactured and produced the earliest version of an engine with a hemispherical chamber in 1903; a two-cylinder engine that delivers 20 horsepower. It was only in the 1930’s that Chrysler started to develop and test an engine with a hemispherical chamber for its own models.

Chrysler Airflow Automobile

Chrysler opted to develop the Hemi engine because their Airflow automobile concept wasn’t positively received in the market because the design of the vehicle was considered as too futuristic during that time. The Chrysler Airflow automobile is a vehicle produced by the company from 1934 to 1937. Chrysler engineer, Carl Beer, was the man behind the Airflow automobile. Beer was able to conceptualize the Airflow by watching a flock of geese in flight, only to realize that he was observing a military aircraft squadron. With this in mind, Beer was determined to produce a vehicle using streamlining to minimize air resistance, a concept that is now known as aerodynamics. Beer’s idea resulted into a fundamental change in vehicle design, but had been a failure because people didn’t buy his concept.

To revamp the Airflow failure, Chrysler started testing the HEMI engine for its vehicles in 1937. The automaker continued to develop the HEMI engine through World War II.

The Republic P-47 Thunderbolt fighter jet (Photo by Kogo)

During the Second World War, Chrysler worked on the Hemi engine as its factories yielded for military production. In line with this, Chrysler developed their first Hemi engine for the Republic P-47 Thunderbolt fighter jet. Chrysler equipped the P-47 with a XIV-2220 Hemi engine that delivers 2,535 PS. The automaker also powered the M47 Patton tank with a V12 Hemi engine.

After the war, Chrysler Chief, K. T. Keller gave the go signal for the production of the Hemi engines. As a result, the 331 cubic inch (5.4-liter) V8 engine was produced.

In late 1950, Chrysler used to their advantage the military experience they had with the hemispherical combustion chamber as they introduced the overhead-valve V8 engine. This marks the birth of the “Fire Power” engine; Chrysler dropped the word Hemi.

Chrysler Chief of Engineer Development, William Drinkard, was the one who established the standards for the Hemi engine. Drinkard stated that all bearings, valve rings and pistons must have a 100,000 mile (around 161,000 km) lifespan. However, Chrysler had a major problem with the camshaft because it tends to wear due to heavy friction between the camshaft lobe and valve tappets. So, the engineers replace the material used for the tappets and added a coating to adhere the problem. After further testing, the HEMI didn’t have major problems after running for 500,000 miles (about 804,000 km). With this, the HEMI engine was ready for mass production.

The 1951 Chrysler Saratoga Club Coupe

The first Fire Power engine was a 5.4-liter that can generate 183 PS. It was first used with the 1951 Chrysler Saratoga Club Coupe due to the vehicle’s lightweight body as the Fire Power engine was heavy.

Thirteen years later, the second generation Hemi engine was introduced in 1964. Subsequently, this year also marks the muscle car era. The second generation Hemi engine was a 426 cubic inches (7.0-liter) that was specially built for racing and driving fast. There were two 426 engine produced, “Circuit” or “Track” and “Acceleration” or “Drag”.

The Gen II 426 race Hemi engine was first introduced at the Daytona 500 in February 1964 with driver Richard Petty winning the race onboard a Plymouth. Petty had managed to secure the NASCAR championship in 1964 with Hemi-powered vehicles.

However Chrysler was forced to withdraw from NASCAR in the following season because the sanctioning body ruled that all engines used for its races must be available on the production vehicles. 

In 1966, Chrysler introduced the 426 Street Hemi for production vehicles and was able to make its comeback to NASCAR racing. During the next several years, vehicles powered by Hemi engines had won countless races and numerous championships.

With the availability of the 426 Street Hemi, Chrysler ceased production of a special drag racing engine. The only exception was the limited edition 1968 Dodge Dart and Plymouth Barracudas that were remained to be equipped with the 426 Race Hemi, with only 75 units of each model produced.

Since the debut of the Gen II 426 Hemi engine in 1964, it still remains a legend not only to its performance on and away from the racetrack, but how it managed to revolutionize the power under the hood.

Dodge Challenger R/T

Chrysler still proudly produces the Hemi engine  with all of their rear-wheel and all wheel drive models. Moreover, Hemi maintains to be the preferred engine in vehicles such as the new generation Dodge Challenger R/T and the Chrysler 300 series.

Clearly, the dedication and hardwork of Chrysler paid off as the HEMI engine continues to be the desirable icon under the hood, a reputation it has had since 1964.