For all those gearheads who, in one way or another, have been involved with American V8s, the world HEMI means something special: the one engine that stands apart from the crowd; the “king” of the pack. But what makes this engine so special? Well, great ideas are, generally speaking, simple ideas, and the “HEMI” engine is no different. “Hemi” is the short for “Hemispherical Combustion Chamber” and that is exactly where the magic happens.
Basically, the difference between a Hemi and an ordinary V8 resides on the heads, everything else is pretty much the same. The shape of the cylinder head’s combustion chamber is approximately half of a sphere. This allows the intake and the exhaust valves to be placed one in front of the other, creating a direct, straight flow of the gases (fuel and exhaust in the picture above).
Another important aspect is the position of the spark plug, located at the top-center of the chamber, which shortens the burn distance of the air/fuel mixture. Those simple solutions make the Hemi engine extremely more efficient than a conventional one. The picture above shows a “flat-top” piston, which does not happen in real life, due to the hemisphere shape, flattop pistons could not produce sufficient compression, so domed pistons were used to make up the difference.
Well, if the Hemi design is much more efficient, why not all the brands have adopted it at the time? The answer is pretty simple: the greatest advantage of the HEMI can also be its biggest inconvenience, which is its physical size. Having the valves (intake and exhaust) lined up one in front of the other requires a considerably wider cylinder head and a complex rocker arm geometry, making the engine not very practical in an assembly line, unless if installed in full-size cars.
In a regular V8, the valves are placed side-by-side, allowing the engineers to design more compact engines and fitting them into smaller cars.
Chrysler didn’t invent the Hemi engine, the design had been around since 1901 and a few European companies like Alfa-Romeo, Jaguar, and Aston Martin had produced engines with this configuration before.
The first Hemi engine built by Chrysler was actually a massive 36 liter, water-cooled V-16, intended to power one of the most famous American fighters of WWII, the P-47 Thunderbolt. Later on, during the development, the Chrysler engine was replaced by a Pratt-Whitney radial engine and the Chrysler Hemi never went into production. On the other hand, the engineers who worked on the project gained valuable experience with the Hemi concept which they later applied to somewhat smaller engines.
In 1951, Chrysler unveiled its three most luxurious models, the New Yorker, the Imperial, and the Saratoga, all of them equipped with the all-new, 180HP, 331CI Hemi V8. At this time, the badge “HEMI” was yet to be adopted and the company named the new engine “FirePower”.
DeSoto, which was the second most prestigious brand in the Chrysler universe, received its Hemi in 1952 and named it “FireDome”. The DeSoto’s Hemi was a bit smaller, 276 CID, and able to crank up 160HP.
Dodge was the last one to receive the Hemi, in 1953. It was the smallest of the gang, with 241CID and with only 140HP. Dodge wasn’t seen as neither a performance nor a luxury brand at the time and for that reason they got the most “tamed” version of the Hemi.
Oddly enough Dodge named the engines: “Red Ram” for the cars and “PowerDome” for the trucks.
Plymouth was the only Mopar brand that didn’t receive the Hemi at that time, but Chrysler had more daring plans for the company: in 1951, the Engine Research Division was developing a Dual Overhead Camshaft, Hemi V6, displacing 235 cubic inches.
The new engine was meant to replace the venerable Plymouth “Flathead” in-line 6 that was in production for decades.
Compact, powerful, and fuel-efficient, the new Hemi V6 was way ahead of its time; when you think about it, the Overhead Camshaft concept would only become popular during the 1980s. Unfortunately, the project was scrapped due to the unusual design and the high production costs.
The Hemi engines produced between 1951 and 1958 are generally called “First Generation” and they range from 241CID (Dodge) to 392CID (Chrysler). The race teams across the USA quickly took advantage of the qualities of the Hemi and also learned how to squeeze even more power out of them. Soon those engines became dominant on the race tracks.
The American automakers have always been using the Stock Car races as an advertising tool and Chrysler didn’t waste much time before offering its new engine to the teams along with all the necessary factory support.
The results came quickly, in 1955, the new Chrysler 300-C, powered by a 331CID “FirePower” engine, completely dominated the NASCAR season. It was the first American car to break the 300 HP mark, more than enough to push the car to an astounding 27 victories and to give Chrysler the Constructor Championship.
When we think about a European roadster powered by an American V8, the first car that comes to mind is the Shelby Cobra, but 11 years before the first Cobra left the assembly line, the American entrepreneur and sports car enthusiast Briggs Cunningham, built a series of European style roadsters, powered by the Chrysler Hemi engine.
Cunningham’s ultimate goal was to win Le Mans with a car 100% made in America and the team’s performance during those years was nothing short of a success.
In 1952 the C4-R driven by Briggs Cunningham himself and Bill Spear finished fourth overall at Le Mans.
The best year for the team was 1953, a C4-R won the Sebring 12 Hours, and at Le Mans, the C5 R driven by Phill Walters and John Fitch finished first in the GT class and third overall. The two other Team Cunningham cars finished seventh and tenth.
The team returned to Le Mans in 1954 to its last attempt to win the race. They took third and fifth place overall. All those cars were powered by the 331CID Chrysler FirePower.
As we can see here, the American challenge to bring down the European dominance in Le Mans had started way before Ford vs Ferrari, in 1966.
At this point, the Hemi had already proven to be an amazing engine on race tracks, but, perhaps, in no other place, the engine had a greater performance than on the drag strips.
The drag teams quickly learned that the early FirePower engines had lots of room for improvement, with some internal rework they could substantially increase the already massive torque of the engine.
In 1958, Chrysler unveiled the biggest of the early Hemis, the 392CID and immediately it became the engine of choice for most of the drag race teams.
Topped with “roots” supercharger and fuelled with nitromethane, those Hemis could easily reach 1500 plus horsepower.
The Chrysler Hemi is a very sturdy engine but it has its limitations, in the beginning of the 1960s, the teams had already reached the structural limits of the factory cast-iron block and cylinder heads of those engines. That was the opportunity for some high-performance parts companies like Keith Black and Donavan to start the production of extra reinforced aluminum engine blocks for competition purposes.
The video above shows a Top Fuel dragster, powered by a Keith Black 3000HP HEMI engine. The car belongs to Powertech, a speed shop in Brazil, which I worked as a parts consultant, for more than 8 years.
The numbers of a modern-day Top Fuel dragster are nothing less than stunning: The 500CID, all-aluminum Hemi V8 burns a mixture of 90% of nitromethane and 10% of methanol and can crank up between 7,000 and 10,000 HP.
It takes 0.84 seconds for a Top Fueler to accelerate to 160 Km/h from standstill. At launch, drivers are subjected to up to 4.75 g–more than a space-shuttle astronaut.
The fastest speed achieved in a National Hot Rod Association in the Top Fuel class is 338.17 mph (544.23 km/h), by Brittany Force at the NHRA Nationals on 1 November 2019 in Las Vegas, Nevada, USA. Force’s record-breaking run came during qualifying. She took only 3.659 seconds to run the 1,000 ft drag strip.
In an attempt to curb the insane top speed of those cars, the length of the strip was reduced to 1,000 ft from the traditional 1/4 mile, 1,320ft.
All those crazy numbers are achieved with engines that still hold the same basic design of the 1951 Chrysler Hemi.
The Second Generation.
After only 8 years in production, Chrysler decided to pull the plug on the Hemi; it was an arguable decision indeed, the engine was efficient and powerful but it was also complicated to build and awkward to fit in the engine bay. But this hiatus didn’t last long, in the early 1960s, it was clear that the “Horsepower War” between the American automakers would be gruesome, and Chrysler decided to bring back its big gun.
Initially, the idea was to build the new Hemi exclusively for competition. Once again Chrysler was aiming at the two most popular forms of motorsports in America: NASCAR and drag racing. This second-generation brought two important features: first, Chrysler finally trademarked the brand “HEMI”, making it the official name of the engine, and second, they unceremoniously increased the displacement to 426CID, well into the “Big Block” territory. The new engine became so physically big that the technicians quickly nicknamed it “Elephant”.
It is not easy to precisely tell the specs of the racing 426 engine, but it is somewhere around 500HP, with 490 ft-lbs of torque at 4000 RPM.
If Plymouth was denied the opportunity to have its own Hemi back in the 50s, now Chrysler granted the brand to be the first one to receive the “Elephant”.
The 1964 Belvedere was the chosen model to represent the “Mopar Nation” in the NASCAR season.
On the third race of the year, in Daytona, the Plymouth finished on 1st, 2nd, 3rd, and 4th positions, giving an idea of how things would be throughout the season.
The HEMI powered Plymouth crushed the competition so easily in 1964, that Ford and Chevrolet joined an effort to pressure NASCAR officials to change the rules for the next year, in an attempt to ban the new Chrysler engine. The pressure from the two biggest American automakers worked and NASCAR came up with a new rule, forbidding “purpose-built” engines. In other words, if Mopar wanted to keep the HEMI on the tracks, they need to sell to the public at least 500 “street legal” cars equipped with the 426.
For the 1965 season, Chrysler decided to withdraw its team rather than equipping the cars with some other engine. The company spend the year rearranging the assembly lines to receive the 426 HEMI.
For 1966, a few mid-size Chrysler models were selected to receive the street HEMI: the Belvedere, the Coronet, and the much anticipated “Sports-Fastback” from Dodge: the Charger.
The HEMI-powered street Mopars were not, by any means, your average Muscle-Car: they were expensive, the customer paid extra US$ 718.00 to have the 426 under the hood, equivalent to US$ 4,700.00 today, and they were not so easy to find, since Dodge and Plymouth built, all together, only 3,300 units that year, just enough to homologate the engine to compete in NASCAR.
On top of all those “inconveniences”, the extra powerful and torquey engine made them too “rude” to be used as regular daily drivers.
The HEMI-powered cars feel more at home on the drag strips than on the streets and there is the place where most of those cars ended up.
What, at first, seemed to be an unfair game played by Chevy and Ford, turned out to be a blessing in disguise: the new NASCAR rule pushed Chrysler to make the new 426 HEMI available for the public, helping to perpetuate the legend of the engine.
In 1966, the 426 was again at NASCAR. Dodge failed to win the manufacturer’s title but David Pearson won the driver’s championship at the wheel of his HEMI Charger.
The “Elephant” became so dominant in NASCAR and drag racing, that in 1969, Ford came up with its own version of the hemispherical heads engine: the 429 “Boss” V8. Just like Chrysler did 3 years before, Ford had to put on the streets 500 units of his new engine to homologate it for the race tracks. The chosen car for the task was the Mustang, even if the Ford engine wasn’t as successful as the HEMI, the 429 “Boss” Mustang became the “Holy Grail” for the Ford collectors around the world.
According to Allpar.com, only 10,904 426 Hemi-powered street Mopars left Dodge and Plymouth assembly plants from 1966–71. The engine was available for pretty much all the Mopar Muscle Cars during those years but the production was very restricted.
Not only the raw performance but also the scarcity of those cars that sealed their status as legends.
Perhaps no other brand captured the “badass” attitude of the Muscle-Car Movement, as well as Mopar, did, but just like everything else in life, good things don’t last long.
The Final Duel.
The design of the 1968-70 Dodge Charger made them one of the most desirable Muscle Car ever produced but, aerodynamically speaking, they are a disaster. Dodge had been working hard to fix this flaw and make the car more competitive for the superspeedways of NASCAR, and after the fiasco of the 1968 Charger 500, Dodge decided to go to the extreme.
For the 1969 NASCAR season, they unveiled the most unorthodox Muscle Car ever, the Charger Daytona. The car, which is a “B” body Mopar (either a Dodge Charger or a Plymouth GTX) with some radical body modifications, was designed to cut through the air more easily at high-speed. A huge 23-inch-tall (584 mm) stabilizer wing on the rear deck keeps the rear end glued to the pavement and a special sheet-metal “nose cone” that replaced the traditional receded front grille, drastically increased the aerodynamic coefficient.
Besides a good start in the season, The HEMI Charger Daytona wasn’t able to stop the Ford Torino “Talladega”, now equipped with the hemispherical 429 “Boss” V8, to win the Championship. It seemed that the Chrysler HEMI had finally met its match.
For the 1970 season, Plymouth presented its own version of the “Aero car”, the Superbird. The fans called both cars, the Daytona and the Superbird “Winged Warriors”.
The feud ” Ford vs Chrysler” continued full throttle, on March 27, 1970, during the Talladega 500, Buddy Baker, driving the No. 88 “Chrysler Engineering” Dodge Charger Daytona, was the first driver in NASCAR history to break the 200 mph (322 km/h) mark.
Dodge won the constructors championship that year and the fans were pretty excited about the next season since Ford had an “aero” version of the Torino ready to join the fight.
But the NASCAR officials decided to put an end to this party. They were (rightfully so) concerned about the extreme speeds those cars were able to reach and in the name of safety, new rules were imposed to slow things down a little bit. First, they lowered the maximum displacement for the Aero cars to 305CID, and later on, they banned those cars for good.
In 1971, Richard Petty decided to drive a Big Block “regular” Plymouth instead of a small block “Aero” and he proved to be right; that was the last time the venerable HEMI 426 won a championship
After 1971, both Chrysler and Ford phased out their hemispherical V8s, it was a wild but short ride. At the same time, the whole Muscle Car Movement was slowly dying, thanks to high insurance costs and the oil crisis from the 1970s.
Th legend didn’t die completely, Mopar maniacs still can buy a brand new, crate 426 HEMI, as Chrysler keeps a small production of the engine as “performance part”.
The Chrysler HEMI represents the peak of the Golden age of the American high-performance cars, and all this respect and admiration hasn’t faded away even after 70 years since the first one hit the streets.
Note of the editor: Although I had the intention to write about the third generation of the Chrysler HEMI, I decided to leave it out of the post. The writing had gotten already too long and I didn’t want to break the post into two parts. Maybe I will address the subject in the future.