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History Of The Mighty Hemi

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  • The first Chrysler engine with hemispherical heads was this supercharged 16-cylinder aircraft engine developed for fighter planes during World War II. It looks as if it is upside down, but the engine was designed to operate with the inverted “V” configuration. This example is on display at the Walter P. Chrysler Museum, next to DaimlerChrysler’s Auburn Hills, Michigan headquarters ( - 2
  • The car that really put the Hemi on the map was the 1955 Chrysler C-300 – the first of the “letter” cars. Its 331-cube mill, with a high-lift cam and a pair of carburetors, was rated at 300 horsepower – an astounding feat in its day. - 3
  • Early Hemi engines were adopted quickly by forward-thinking racers, including a team of Chrysler engineers who founded what would become one of the most famous drag racing teams of the 1960s and early ’70s: the Ramchargers. This is a reproduction of their first groundbreaking race car (on display at the Walter P. Chrysler Museum), which was much faster than it was pretty. - 4
  • Dodge’s version of the original Hemi was called the Red Ram. In the first epoch of Hemi production, 1951-59, Dodge trucks were the last vehicles to offer a Hemi. Less expensive, less complex wedge-head engines replaced the Hemi at the end of the 1950s. - 5
  • The second coming of the Hemi began in the 1960s, with the 426-cubic-inch Hemi engine. In production cars, it was called the Street Hemi and was rated at 425 horsepower. The Street Hemi was available from 1966 through 1971. - 6
  • Hemi-powered Dodges and Plymouths, such as this 1971 ’Cuda, were the most feared factory performance vehicles of the muscle car era. Today, they are the most collectible. - 7
  • The 426 Hemi’s legacy began on NASCAR’s speedways in 1964. The engine was banned, at first, until Chrysler made versions available in production vehicles. At the end of the decade, the Hemi’s power combined with the advanced aerodynamics of the winged Plymouth Superbird and Dodge Charger Daytona (shown here) prompted another ban. - 8
  • Compared with the 426 Street Hemi, the NASCAR racing version used aluminum cylinder heads and a single four-barrel carburetor. Camshaft performance, too, was designed for the sustained high-rpm operating range of stock car racing. - 9
  • Vintage Hemi muscle cars are still the stars of any cruise night or car show. This collection of Mopar muscle machines is gathered along famed Woodward Avenue, in the suburbs of Detroit. - 10
  • Work on the new Hemi engine began in the late 1990s. Although development of the new Hemi was mostly secretive, Chrysler hinted at the engine’s rebirth. This 2000 concept car was none-too-subtly named the 300 Hemi C. - 11
  • Robert Lee, Chrysler Group’s Vice President of Powertrain was involved with the new Hemi’s development and is the foremost expert on the engine’s design and capabilities. - 12
  • DaimlerChrysler’s rear-drive LX-platform cars, including the Dodge Magnum R/T, the Charger R/T and Chrysler 300C brought Hemi power back to Mopar muscle cars after more than a 30-year absence. The 2006 Dodge Charger Hemi Super Bee is shown here. - 13
  • A 6.1-liter version of the new Hemi was released for the 2005 model year. It was rated at 425 horsepower and 420 lb.-ft. of torque. The engine was released in a variety of high-performance SRT8 variants of Dodge, Chrysler and Jeep vehicles. A 300C Hemi SRT8 is shown. - 14
  • Perhaps the ultimate nod to the Hemi’s legacy, as well as the public’s nostalgia for muscle cars, is the 6.1L-powered Dodge Challenger concept, which was introduced in 2006. The Challenger has been given approval for production in 2008. - 15
  • In 2006, Chrysler began offering specially equipped, Hemi-powered Dodge Charger and Magnum models to police agencies – all with the heavy-duty equipment expected of special service vehicles. Doughnuts, however, are not included. - 16
  • The Chrysler 300-C was an extremely handsome car in 1955 and both it and its progeny are still knockouts fifty years later. - 17
  • There was no mistaking fifties Chrysler products for any other brand. Everything about the Chrysler letter cars was bold and powerful. - 18
  • Big, bold egg crate type grilles have been a Chrysler letter series signature styling cue. - 19
  • This is the engine that started Act II for the Chrysler Hemi—the 1964 426 cubic inch Race Hemi. When these engines were installed in factory lightweight cars (with lots of aluminum body parts) they were virtually unbeatable at dragstrips. - 20
  • The ultra rare, super desirable ’71 Hemi ‘Cudas are finding their way to the best automotive museums. It seems like a musclecar collection isn’t complete without one. - 21
  • The rear ¾ view of a Dodge Daytona illustrates what a swoopy, wedge-like shape the car had for minimizing aerodynamic drag. The race inspired rear wing has recently shown up on some of the hottest Japanese rocket cars. - 22
  • The massive air cleaner for the dual quads on a Street Hemi almost hides the top of the engine. - 23
  • Comparing the current generation Hemi to the Street Hemi shows how much they’ve changed visually, but the underlying design is still based on the hemispherical combustion chamber. - 24
  • This super rare ’71 Hemi ‘Cuda (one of 108) was a feature attraction at a recent R-M Auction. The Rallye Red car was loaded with options such as leather seats, rear window louvers, AM/FM/tape player, 4-speed and rear wing. Bidders need to bring enormous checkbooks when trying to own a ’71 Hemi ‘Cuda. - 25
  • NHRA Funny Car stars such as Gary Scelzi ably carry the Hemi banner. The basis of all nitro-burning Top Fuel and Funny Car powerplants is the venerable Hemi. - 26
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by Barry Kluczyk  More from Author

Looking Back On Three Generations of Hemi Power

Like so many innovations to burst from Detroit in the years following World War II, Chrysler’s first production “hemi” V-8 had its roots in the war effort. As the United States’ tremendous manufacturing capability switched from supporting a market economy to dedicated war production, civilian automobile production ceased for nearly four years. Concurrent with war production, the engineering and design departments of the auto companies focused their attention on the needs of the military – with familiar production auto engines and transmission powering tanks and other military vehicles.

Pressing light-duty passenger car engines into service in heavy-duty – and just-plain heavy – military vehicles was a compromise. During the war Chrysler began experimenting with hemispherical cylinder head designs, as a way to increase efficiency – pushing more air in and out would boost the power of an engine without the need to increase displacement. The “hemi” name is derived from the hemispherical shape of the cylinder head’s combustion chambers. The hemi design’s attractiveness to engineers stemmed from the domed chamber’s intrinsic ability to support high compression with little worry of detonation, compared to a traditional – and more compact – wedge-type cylinder head.

The efficiency of the hemi engine led Chrysler engineers to draw up 12-cylinder and 16-cylinder designs for tanks and planes, although none were put into production. However, a prototype supercharged V-16 aircraft engine was built and tested in a P-47 Thunderbolt fighter. The engine was inverted – the cylinder “V” pointed down, while the crankshaft was “on top” of the engine. It produced approximately 3,000 horsepower.

Chrysler introduced its first production vehicles with hemispherical-head V-8 engines for the 1951 model year. The engine was dubbed the “FirePower” V-8 and was standard in the Chrysler New Yorker, Crown Imperial, Imperial and Saratoga. The FirePower V-8 displaced 331 cubic inches, had a 7.5:1 compression ratio and was rated at 180 horsepower – a 45-horsepower jump over the previous year’s 324-inch, 135-horse inline eight-cylinder.

The hemi configuration of the FirePower V-8 that was available in the 1951 Chrysler line gave the company a marketing edge to use against competitors, including Cadillac’s groundbreaking overhead-valve V-8 that was introduced in 1949. Coincidently – or, perhaps, not coincidently – Chrysler’s 331-cubic-inch FirePower V-8 featured the same displacement as the Cadillac V-8. Yet, the hemi-headed FirePower V-8 enjoyed a 20-horsepower advantage over the Cadillac.

It didn’t take long for the public to acknowledge the performance of the hemi engine and Chrysler, recognizing a product hit with greater potential, started to spread hemi engine design through the rest of its family of vehicles. In 1952, DeSoto offered a smaller, 276-cubic-inch hemi V-8 called, appropriately enough, the FireDome. It produced just 160 horsepower, but it still enjoyed an advantage over most of the competitors in its price field. Dodge introduced the Red Ram hemi in 1953 and made hemi engines a staple of its truck line throughout the 1950s. The only brand left out of the hemi revolution that decade was Plymouth, which soldiered on with conventional inline six-cylinder and eight-cylinder engines – although Plymouth did offer a “poor man’s” hemi in the form of the poly-head V-8 in 1955 and ’56, a sort-of semi-hemi that was lighter and less costly to produce.

It was Chrysler’s famed “letter series” cars, however, that established the hemi engine’s mythic reputation, with milestone horsepower ratings and twin-carburetor induction. When introduced in 1955, the 331 hemi engine in the C-300 was rated at 300 horsepower.

Dodge’s first hemi engine, the 1953-introduced Red Ram, was the smallest and least powerful of the family, measuring just 241 cubic inches in displacement and producing only 140 horsepower. Given Dodge’s position in Chrysler’s marketing pecking order, this wasn’t surprising. Nevertheless, it still topped the best Ford offering that year, which was a 239-cubic-inch version of the long-in-the-tooth flathead V-8 that mustered just 110 horsepower. Chevrolet didn’t even offer an eight-cylinder in 1953; its small-block V-8 was still two years down the road.

Despite its much-heralded reputation at the beginning of the 1950s, there were no production hemi engines available in Chrysler products by 1960. They ceased production in passenger cars after the 1957 model year and Dodge trucks stopped offering them after 1959. The reasons why the hemi disappeared after less than 10 years on the market were simple: complexity and cost. The hemi was a complicated and costly engine to produce, while advances in combustion technology were making the simpler wedge-head engine more efficient.

Enter the Street Hemi


Chrysler revisited the hemi-head design in 1964, when it introduced a hemi-style racing engine for the NASCAR circuit. It was an auspicious reintroduction of the engine design, as 426 Hemi-powered race cars finished first, second and third at the ’64 Daytona 500. Richard Petty won the race, after leading 184 of the 200 laps in his Plymouth – including lapping second-place finisher Jimmy Pardue when the race was only half done.

Not surprisingly, the immediate and obliterating success of the new Chrysler Hemi racing engine caused a stir, particularly among those racers who didn’t have one under the hood. After a few more races with similar results, NASCAR moved to restrict Chrysler’s not-so-secret weapon by imposing a “production model” rule. This meant that, for the 426 Hemi to be legal in NASCAR competition, it had to be offered in meaningful quantity in regular-production street cars.

Chrysler was unprepared to offer the racing-only 426 Hemi in street cars. The company sat out the ’65 season while it prepared to retaliate. They returned in 1966 with the all-new, 426 Street Hemi and Chrysler quickly went racing again. There was little that was significantly different between the racing engine and the street version. The Street Hemi received two four-barrel carbs (the racing version had a single carburetor), lower compression, different valve timing and iron cylinder heads. There were a few other minor differences, but the street versions were, for all intents and purposes, simply detuned versions of what Petty was using to run rings around the competition.

In 1966, the 426 Street Hemi was rated at 425 horsepower (gross) and 490 lb.-ft. of torque. It would remain in production through the 1971 model year, with its horsepower rating unchanged. Only a handful of changes were made to the Street Hemi during its production run, including upgrades in 1968 to reduce oil consumption and a change to a hydraulic camshaft and lifters in 1970.

Street Hemi-powered cars quickly became the stuff of legend and myth at small-town burger stands and urban street-racing venues. They developed a reputation for being unbeatable – when they were properly tuned. The fact was the twin-carbureted engine, with its high compression and high-rpm performance intentions, suffered when loped around at low speeds. The carbs loaded up and the plugs often fouled. The engine required constant attention and tuning, particularly the carburetors, but when all the dials lined up the only thing that could catch a Street Hemi was another Hemi.

Hemi-powered Road Runners, GTXs, Super Bees, as well more subtle muscle cars, became icons of their day. And in the decades since the muscle car era faded, it’s these elephant-engine Mopars that command the highest prices in the muscle car collector world. The most valuable of these are the 1970 and ’71 Hemi ’Cudas, of which only 666 were built in 1970 (652 coupes, 14 convertibles) and a mere 115 in ’71 (108 coupes, seven convertibles).

Following closely behind on the value scale with the ’Cudas are the NASCAR-inspired 1969 Dodge Charger Daytona and 1970 Plymouth Superbird. These cars featured wind-cheating nosecones and sky-high rear wings, which were designed to make the car more aerodynamically efficient (and therefore faster) on NASCAR speedways. Chrysler played by the rules and claimed to offer enough examples to the public to make the cars eligible for racing. Truth be told, only a comparative few production models were sold; a little more than 500 Charger Daytonas and 1,935 Superbirds.

Like the original 426 Hemi racing engine in 1964, the “winged warrior” Daytona and Superbird models caught the competition unaware. The cars, with their slippery shapes and high-winding Hemis, dominated NASCAR’s tracks and were the first to crack the 200-mph barrier. Again, NASCAR came down on the Mopar group, banning the Daytona and Superbird after the 1971 racing season.

The Street Hemi was done after 1971, too, as tightening emissions regulations, soaring insurance premiums on muscle cars and the general public’s drift away from the muscle car scene contributed to its demise. Still, its legacy was supported by legions of racing enthusiasts who still used the engine in drag racing and amateur stock car racing. Its mystique intensified, too, as dusty, forgotten and forlorn muscle cars were pulled from barns and side yards in the decades after production ended, reigniting interest in an unprecedented period of American automotive history.

Third-generation Hemi


The Chrysler Hemi engine has achieved mythical status among enthusiasts, as well as instant recognition from even the most passive automotive consumer. It’s not surprising, then, that DaimlerChrysler had a hit on their hands when the next-generation Hemi was introduced for the 2003 model year (arriving in calendar year 2002). Initially offered in the Dodge Ram 2500 and 3500 pickups, the Hemi quickly spread to the company’s new line of expressive rear-drive passenger cars, including the Chrysler 300C and Dodge Magnum.

Development of the engine that would become the new Hemi began in the latter half of the 1990s. Chrysler engineers faced the realization that the stalwart 5.9L Magnum V-8 truck engine – an engine known more commonly by its 360-cubic-inch displacement and whose basic architecture originated in the 1950s – wouldn’t meet the performance requirements of the coming decade. This included not only the horsepower and torque figures Chrysler needed to remain competitive with new products from General Motors and Ford, but also the federal mandates for emissions and fuel economy.

Retired Chrysler engineer Rich Schaum initially proposed the new V-8 to Robert Lee, Chrysler’s Vice President of Powertrain Engineering, in 1996, but the word “hemi” was never mentioned. As the engine would be an all-new, “clean sheet” design rather than an update of existing engines, the engineering staff evaluated a variety of engine configurations.

The evaluation process was centered on finding the “just right” combination of factors that would deliver big power with emissions- and fuel-efficiency. One of the studied engines that delivered on all of Chrysler’s wants, albeit on a smaller scale, was the water-cooled flat-six engine of the Porsche Boxster. It just so happened that the Boxster engine had hemispherical combustion chambers.

But, the hemi design came with baggage: Although the old Street Hemi made tremendous horsepower, it was terribly inefficient when it came to economy and emissions – two of the very reasons that killed it in the early 1970s. A lot of unburned fuel went out the tailpipes of Street Hemi-powered cars. Nonetheless, the basic hemispherical chamber design enabled great power and Chrysler engineers began to work on ways to increase the efficiency of the design.

The first new Hemi engine prototype was started ceremoniously and without a hitch, but the engine had not been officially named a “Hemi” – although its design left little doubt. The original name, given even before the decision to go with a hemi design, was “Ram.”

As the third-generation Hemi was an all-new engine, from the main bearings to the throttle body, pre-production validation was thorough and extensive. Prototype engines were aimed at a 150,000-mile minimum for 95th percentile drivers – meaning only 5 percent of owners would theoretically treat the engines harder than Chrysler’s engineers for the first 150,000 miles. To achieve the lofty durability goals, the engineers racked up some impressive numbers: 11 million “customer equivalent miles.” In other words, the testing procedures encompassed the equivalent of 11 million miles of typical customer use. Some of those equivalent miles came from testing 16 engines to double the 150,000-mile lifespan.

Testing didn’t end when the production line started, either. The first 1,000 production engines were dyno-tested to ensure performance targets and consistency. After those first thousand engines, every new Hemi off the line is “cold” tested – cranked over during an inspection, but not fired.

And while it should come as no surprise to learn the new Hemi beats the pants off the old 5.9L engine when it comes to emissions, the Hemi also achieves approximately 10 percent better fuel economy, while offering significantly more power.

 Simply put, the third-generation Hemi is the best yet.


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