The History Of The First HEMI Engine

Stellantis, the parent company of Chrysler and RAM, caused quite a ruckus in 2024 when it announced it would discontinue the legendary HEMI engine in its RAM trucks. However, the blowback from this change prompted the company to quickly reverse course, and in 2025 it was announced that the HEMI would be reintroduced in the 2026 RAM. In the press release distributed by Stellantis, the CEO of the RAM brand Tim Kuniskis even called discontinuing the HEMI a “mistake”.

Perhaps it was — after all, this iconic power plant has been beloved ever since the 1951 production debut of the FirePower, Chrysler’s very first HEMI engine. However, the true history of the HEMI goes much farther back than that. In fact, it starts about half a century before the Chrysler FirePower ever saw the light of day. A HEMI engine would win a Grand Prix and another one would join the Allies in World War II well before Chrysler would start using it in its production automobiles.

While the name HEMI is closely associated with Chrysler and other members of its family of brands — most notably Dodge and RAM — the automaker did not invent the engine, even though it would eventually trademark the name. Here’s the full history of the HEMI legacy.

The very first HEMI engine was likely used to power a boat, and the first HEMI engine used in a car was only a 4-cylinder. Though there is not a clear consensus, many historians credit Chelsea, Wisconsin resident Allie Ray Welch with inventing the concept. He built a two-cylinder prototype in 1901 and used it as the motor for a boat.

The first time an automaker put one in a car was in 1905, by a Belgian company named Pipe.  A little later, the Premier Automobile Co, of Indianapolis would place a HEMI engine in a race car. The Premier could crank out 100 hp at 1,000 rpm. Due to the weight of its engine, the car would be disqualified from all but one race, despite the best efforts of its owner Carl Fisher. That race was at the Indiana State Fair, where it won by reaching the alarming speed of 59 mph.

Other manufacturers, like Fiat, Peugeot, Alfa Romeo, Daimler, and Riley would also start producing cars with HEMI engines in the first part of the 20^th century. Felice Nazzaro drove a HEMI-equipped Fiat to victory in the 1907 Grand Prix, winning that race by over six minutes. The HEMI design, or variations of it, have been used in race cars since then.

The appeal of the engine came for its raw power and unique design. The cylinder head combustion chambers on the early HEMI engines were shaped like one-half of a sphere, or hemisphere — hence the name, HEMI. This makes it possible to place the spark plug top and center, which makes the burn of the air/fuel mixture more efficient. Air flow, meanwhile, is improved by the placement of an intake and exhaust valve on either side of the plug.

Some form of the HEMI engine would pop up here and there after the early years of the 20^th century, but Chrysler had yet to adopt it. That would change during World War II. American automotive manufacturers shifted their focus dramatically from producing civilian automobiles to the war effort. Entire automotive plants would be converted to factories for making tanks, military vehicles, and even airplane engines.

Chrysler was no exception in this regard, as it would build 22,000 tanks over the course of the war. Also notable among Chrysler’s efforts during the war was the development of the experimental 2,500-hp 36.4-l inverted V16 aircraft engine, which was, in fact, a HEMI. It was tested in a Republic P-47 Thunderbolt to great success, reaching over 500 mph. 

However, the war ended before it could be rolled out to production and jet engines pretty much made it obsolete. Chrysler would stay in the military equipment business after the war ended, however, by producing the V-12 AV-1790-5B engine for the cold-war era M47 Patton tank.

Chrysler put to use the knowledge it had gained during World War II and introduced its first V8 HEMI automotive engine in 1951. Interestingly, some say that neither this engine — nor any of the modern Chrysler HEMIs — are true HEMIs. This is because instead of using truly hemispherical cylinder head combustion chambers like the original HEMIs, Chrysler decided to go with a smaller dome shape. That engine wasn’t even called HEMI at first — instead, it was given the name FirePower and internally referred to as the Double Rocker due to its dual-valve configuration.

The automaker put the FirePower engine in three of its cars, the Chrysler New Yorker, the Chrysler Imperial, and the Chrysler Saratoga. It measured 331 cubic inches and was rated at 180 hp. That would be modest by today’s standards, but the Chrysler HEMI outclassed its nearest competition, the 1951 Cadillac, by 20 hp.

Chrysler was so confident in the FirePower that it asked the other brands in the family to develop their own lines of HEMI engines. Soon, DeSoto would produce the Firedome starting in 1952 and Dodge would release the Red Ram starting in 1953. While similar, these engines were all developed separately, as was the practice among sister brands at the time, which meant that their parts were not interchangeable.

Chrysler had thrown down the gauntlet, but other automakers quickly picked it up. Cadillac slapped a 4-barrel carburetor to the engine it installed in its 1952 Series 62, boosting output to 190 hp. Meanwhile, Ford would show up the Chrysler FirePower with big wins for the Lincoln at the Carrera Panamericana endurance race in 1952, 1953, and 1954.

Lincoln’s wins on the racetrack were getting headlines, leaving Chrysler’s reputation at stake. It would respond in 1955 by releasing the Chrysler 300, which was fitted with a FirePower HEMI engine that was rated at an astounding 300 hp. By 1958, competition had pushed Chrysler to produce the 300D configuration for the 392-cubic-inch FirePower V8 engine, which could crank out 380 hp — the highest in the industry at the time. 

Consumers could also opt for a high-performance version of the engine paired with a manual transmission that was rated at 390 hp, although some experts estimate that it could actually reach 435 to 450 hp. Unfortunately, this would be the last production model equipped with a FirePower. Sales had dropped, and the company decided to pivot from HEMI engines to lighter, more efficient wedge-head V8 engines, which were more cost-effective to manufacture.

The FirePower’s racing history began in 1951, when Tom McCahill drove a Chrysler New Yorker at Daytona Beach and won the trophy for the fastest American stock car. After the 1954 Indianapolis 500, Chrysler revealed its 331 cubic inch HEMI engine, which could perform as well as the top vehicles in the race that year. However, Indy officials froze HEMI engines out later that year by decreasing the size limit of engines to 272 cubic inches.

Chrysler returned in 1955 with a fleet of Chrysler 300 super coupes. That year would see that team’s star driver, Tim Flock, win 18 races, including the championship. Buck Baker would win 14 races for the team in the following year. What’s more, the team would win 16 races in a row in 1956.

Chrysler would retire its production and racing Firepower engines in 1958, but racing would prompt Chrysler to resurrect the HEMI engine in 1964, when it created its Gen II HEMI engine to compete in NASCAR. It would dominate the Daytona 500 that year, prompting NASCAR to impose a rule that would restrict Chrysler from using that version of the HEMI engine until it had sold street-legal production models. Chrysler would respond by producing 1966 B-body Dodges and Plymouths with street-legal HEMI engines.

The Chrysler FirePower has both a storied history and powerful legacy. Its successors, the Gen II and the current Gen III HEMI engines, would become integral parts of the company’s model lineup. Sadly, the ICE-powered, HEMI-equipped Dodge Charger and Challenger were discontinued in 2023 in favor of EV versions — but at least the HEMI engine will live on in upcoming RAM trucks.