HEMI Engine Sizes

Discussion about the Hemi in general.

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HEMI Engine Sizes

Post by scottm » Tue Jun 15, 2021 10:29 pm

HEMI Engine Sizes
Charting 70 years of Chrysler Hemi dominance at the track and on the street.
https://www.hotrod.com/articles/hemi-engine-sizes/
While many manufacturers have toyed with building engines with hemispherical combustion chambers, only Chrysler (now Stellantis) has wed itself to the technology to the extent that the name "Hemi" has become synonymous with Chrysler-branded products and many Hemi engine sizes over the decades. As domestic manufacturers fought for engineering supremacy following World War II, it was Chrysler that emerged with unique research produced from an experimental inverted V-16 engine with over 2,500 hp and 36 liters of displacement called the IV 2220. When mounted to the airframe of a Republic P-47D Thunderbolt, the hemispherical IV 2220 was able to sustain level flight at 504 mph at 15,000 feet. Despite this being unheard of for a prop-driven aircraft, the military contract was canceled. New-fangled jet-powered aircraft were the future, but the breakthrough engine still had a role to play, albeit in greatly modified form.

By 1949, both Cadillac and Oldsmobile had introduced new overhead-valve V-8 engines, which were perceived as a premium relative to the flatheads and straight-eights of the era. Overhead V-8 designs were more compact and lighter in weight, and they generated more power per cubic inch than flathead engines due to their breathing efficiency. By introducing the first production Hemi V-8 in 1951 as the Chrysler FirePower V-8, then in 1952 in the DeSoto as the FireDome V-8, Chrysler Corporation was able to leapfrog over GM by adding another crucial technological advantage to the overhead-valve formula: the hemispherical combustion chamber. Let's look at the many Hemi engine sizes Chrysler built over the years.

The First-Generation HEMI

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The half-spherical combustion chamber was superior to ordinary wedge-chambered heads because of its intrinsic octane tolerance and unshrouded pent-roof valve angles. By orienting the valves tangentially on the hemispherical combustion chamber's surface (and putting into place two rocker shafts to support separate intake and exhaust valve rocker-arm rails) the valves could open unshrouded into the cylinder, admitting heretofore unobtainable amounts of air and fuel. Armed with this technological advantage, Chrysler (and Imperial) introduced several Hemi engine sizes, starting with the 331ci as the FirePower in 1951, the DeSoto 276ci FireDome in 1952, and the Dodge 241ci Red Ram in 1953.

In the early years of the Hemi, improvements came in rapid-fire sequence, with each year producing larger Hemi engine sizes, more power, and more compression. Under the Chrysler Corporation umbrella, there wasn't just one Hemi design, but three—one for each brand in the Chrysler, DeSoto, and Dodge lineup. (There would be no Hemi for Plymouth until the second generation in 1964 when the 426ci Race Hemi debuted.) Each division's Hemi engine sizes were an animal unto itself, with the biggest differentiating factor being bore-to-bore centerline distance. For this reason, Hemi parts of different Hemi engine sizes built between 1951 and 1958 do not interchange.

For those contemplating the build-up of a first-generation Hemi, it's worth understanding the differences in Hemi engine sizes, but the most significant to know is that the Chrysler FirePower Hemi—specifically in 1957 to 1958 form with 392 cubic inches—is the one most sought after by vintage enthusiasts, particularly vintage drag racers. 1957 would be the banner year for the first generation of Hemi engine sizes as well as DeSoto's and Dodge's final year, with 1958 being the swan song for the Hemi at Chrysler. (Dodge trucks phased out the Hemi in 1959.) The cost and size associated with the dual-shaft rocker-arm layout and the engine's subsequent wide berth made polyspherical- and wedge-chambered single-rail valvetrain layouts cheaper and more easily packaged.

The Second-Generation 426ci HEMI

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Before the lights went out on the original Hemi around 1958, Chrysler had approached racing tepidly, but nevertheless proceeded cautiously with an engineering bent to gather data. In a project called A311, Chrysler developed the Chrysler FirePower Hemi in a configuration suitable for Indy, ostensibly to do tire testing for Goodyear and Firestone. After the 1954 Indy race, top teams were invited with their cars to Chrysler's new high-speed test venue in Chelsea, Michigan, to do some testing. When Chrysler rolled out a 311ci Hemi-equipped Kurtis Kraft machine that ran as fast as that year's top Indy Miller and Offenhauser contenders, word spread fast. By the end of the year, the engine size limit for Indy was decreased to 272ci to prevent the Hemi from competing. Notwithstanding, the A311 Hemi program did provide the baseline dataset for the second-generation Hemi, which would debut for 1964 as a race-only option in Dodge and Plymouth machines.

The 426ci Race HEMI

Since much of Chrysler's big-block Wedge program had evolved from work done on Hemi engine sizes in the 1950s, it was recognized early on that the path back to stardom in the racing world was most easily accomplished by bringing back the Hemi, rather than a slow, incremental evolution of the Max Wedge. In 1963, when Chrysler directed powertrain engineers Tom Hoover and Don Moore to develop an engine that could win Daytona, the A311 Indy program was dusted off and work began to reverse-engineer a Hemi-chambered cylinder head for the R/B-series big-block. Work was completed on the second-generation Hemi, a 426ci behemoth dubbed the Race Hemi, and it handily dominated the 1964 Daytona 500 with a 1-2-3 sweep.

Furious that Chrysler could steal their thunder out from under them, Ford protested to NASCAR, and by the end of 1964, the stock car sanctioning body had had enough. Despite Ford winning the manufacturer's championship in 1964, a Hemi ban was instituted anyway, and for 1965, all engines that weren't available to the public were banned from competition. Chrysler protested and sat out the 1965 season to concentrate on drag racing.

The 426ci Street HEMI

Chrysler wasn't content to sit out NASCAR just as the performance war was getting started. It had amassed a significant amount of credibility from the Hemi, and there was confidence behind closed doors that a street version of the Hemi could establish Dodge and Plymouth as the reigning kings of the muscle car world. Tired of seeing Fords everywhere and no fans in the stands, NASCAR finally relented and let the Hemi back into competition for 1966, but not without some changes.

To make the Hemi legal for racing, it had to be available to the public with at least 500 examples built for the model year. Chrysler complied with the Street Hemi, a street-ready version based on the Race Hemi of 1964, but with concessions made for durability. A milder cam, less aggressive valve springs, less compression, and heat risers for cold-start drivability were added. At a cost of $900 for the Hemi option, buyers also got the necessary suspension and driveline upgrades needed to handle that power, things that weren't always included with high-horsepower engine options at Chrysler's competitors.

The street Hemi remained an available engine option through 1971, predominately in Dodge and Plymouth B-Body intermediates but also in limited numbers of A-Body Dodge Darts and Plymouth Barracudas for use in drag racing. When Dodge and Plymouth took the wraps off the new E-Body ponycar in 1970, the Hemi option was the top box to check on the order form. These cars would become the pinnacle of Hemi-powered machinery.

The Third-Generation HEMI

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After the bottom dropped out of the performance world in the early 1970s, it would be decades before Chrysler dared entertain the idea of breaking out the Hemi design again. Late to disengage from large cars and large engines, Chrysler found itself burned by its lack of fuel-efficient front-drive offerings and moved hard in that direction for 1981, going all in with the K-car. The move was a success, but by the end of the 20th century, performance was back on the front page again.

Meanwhile, engineering and manufacturing developments had ushered in a domestic revival of high-performance, mostly at Ford and GM. Although Chrysler's engineering resources were still among the best in the business, the product portfolio was not always reflective of this. To take advantage of the new sales success of performance, Chrysler embarked on the development of a new V-8 engine of 345 cubic inches that had a twist on the hemispherical combustion chamber.

The third generation of Chrysler Hemi made a soft introduction in 2003 Dodge Ram trucks as a workhorse that punched well above its weight. Contemporary advertising with the slogan "That thing got a Hemi?" quickly increased the new Hemi's visibility. Available exclusively in Dodge Ram trucks at first, the new 345-hp Hemi enjoyed good reviews and quickly garnered favor among enthusiasts—for the time being in the truck universe.

Fans of modern muscle would finally get their wish in the fall of 2004 with the introduction of the LX platform passenger cars: the Chrysler 300C and Dodge Magnum R/T. (The Dodge Charger R/T would come online as a 2006 model.) At last, the Hemi had come full circle, manifesting itself in the Chrysler 300C—a car that paid more than a little visual and performance homage to the Chrysler Hemi-powered C-300 of 1955.

Behind the doors at Chrysler, the plan was to proliferate Hemi engine sizes and dominate the performance world and the newly formed Street and Racing Technology (SRT) group was tasked with the job. The 345-hp 5.7-liter (345ci) Hemi was put on a regime of steroids and weightlifting, emerging at a buff 6.1 liters of displacement (370ci) and 425 hp. The beefcake 6.1L was an exclusive in SRT's line of SRT8 LX sedans that comprised the Chrysler 300C SRT8, the Dodge Magnum SRT8, the Dodge Charger SRT8, and the (2008-only) Dodge Challenger SRT8 from 2005 until 2008.

Third-Generation HEMI, V2.0

Chrysler was quietly gearing up for the mic-drop return of the Dodge Challenger R/T to the lineup for 2009, and it gave engineers an opportunity to make a series of mechanical improvements to the Hemi to increase power and fuel economy, namely with the addition of variable camshaft timing (VCT) and a multidisplacement system (MDS). Higher-flowing cylinder heads, however, were the main attraction to enthusiasts, and this bumped power output roughly 30 hp, from around 340 hp to (at least) 370 hp. (Some models varied slightly due to differences in calibration, induction, and exhaust, but the change generally hews close to this. )

Called the "Eagle" by insiders, the second version of the third-generation Hemi is currently found under the hoods of rear-drive 2009-to-current Dodge, Ram, Jeep, and Chrysler cars and trucks. At the same time the V2.0 Eagle Hemi hit the streets, SRT was working on the 392ci (6.4L) "Apache" Hemi in SRT8 versions of the 2011 Chrysler 300C, Dodge Charger, and Dodge Challenger, all with 485 hp. Further improvements over the V2.0 Eagle Hemi are found in the intake manifold, cylinder heads, and camshaft, and in the time since the Apache's introduction in 2011, it has made the jump to Ram trucks (2014), the Dodge Durango (2018), and the Jeep Wrangler (2011).

Supercharged Variants: Hellcat, Demon, Redeye, and Super Stock!

Chrysler's competition at GM and Ford certainly weren't dragging their feet. Developments in direct-injection technology were happening at full tilt, and engineers were increasingly cognizant of the fast pace of technology, at Ford with the Coyote/Voodoo V-8 and EcoBoost and at GM with the LT1 and LT4. The engineering folks at SRT, however, were relentless, and nothing short of absolute supremacy would suffice. Beginning for the 2015 model year, Dodge would roll out a series of 700-plus-horsepower Hemis, first with the 6.2-liter (370ci) Hellcat Hemi.

Adding an IHI-sourced twin-helix supercharger in combination with air-to-liquid intercooling via an independent cooling loop allowed unprecedented amounts of power from ordinary 91-octane gasoline, and once introduced in SRT's Challenger, the 707-hp Hellcat Hemi would surface in the Charger (2015), Jeep Grand Cherokee Trackhawk (2018), Dodge Hellcat Durango (2021), and Ram TRX (2021).

The high point of the Hemi came in April 2017 at the New York International Auto Show with the announcement of the 840-hp Dodge Demon. Based on the Hellcat Hemi, the Demon's Hemi engine was rated an additional 101 hp over the Hellcat Hemi, putting out 808 hp on 91-octane fuel. (Just 3,300 Demons were built in 2018.) With a load of 100-octane unleaded race fuel, however, owners could push a button mounted on the vehicle's center stack, and the powertrain control module would change to a race calibration that puts out 840 hp. The Dodge Demon featured a brace of race-specific hardware, including DOT-legal drag radials, electronically controlled drag suspension, line-lock (for burnouts), a transbrake (for drag launches), wide fender skirts to house the oversized drag tires, and other drag-specific features for hardcore enthusiasts.

Once the one-year-only 2018 Dodge Demon had run its course, SRT followed it up with the Widebody Redeye Challenger at 797 hp in 2019 and Widebody Redeye Charger in 2020, using the Demon's supercharger 6.2L Hemi largely unchanged except for it not having the race calibration for 100-octane fuel. Alternately, the reason stated for the Redeye's reduction in power at the 91-octane rating is due to a relative restriction in the Redeye's air inlet tract, which has a slightly smaller flow capacity than the Demon's—otherwise the engines themselves are identical. In 2020, SRT rolled out yet another killer machine in the 2020 SRT Super Stock, which is even more rare than the 2018 Dodge Demon with just 200 built. This time, the Super Stock's Demon Hemi was rated at 807 hp, versus 808 hp in the Demon and 797 hp in the Redeye.

HEMI Engine Sizes by Year

FIRST-GENERATION HEMI ENGINES: 1951 TO 1958

* Chrysler FirePower, 1951 to 1955 (Chrysler and Imperial only), 3.8125-inch bore x 3.625-inch stroke, 331ci
* Chrysler FirePower, 1956 to 1957 (Chrysler, Imperial, and some Dodge trucks 1957 to 1959), 3.9375-inch bore x 3.625-inch stroke, 354ci
* Chrysler FirePower, 1957 to 1958 (taller deck by .5 inch, favored by drag racers), 4.00-inch bore x 3.906-inch stroke, 392ci
* DeSoto FireDome, 1952 to 1954, 3.625-inch bore x 3.344-inch stroke, 276ci
* DeSoto FireDome, 1955 only, 3.720-inch bore x 3.344-inch stroke, 291ci
* DeSoto FireDome, 1956 only, 3.720-inch bore x 3.80-inch stroke, 330ci
* DeSoto FireDome and FireFlite, 1956 to 1957, 3.78-inch bore x 3.80-inch stroke, 341ci
* DeSoto FireDome, 1957 only, 3.80-inch bore x 3.80-inch stroke, 345ci
* Dodge Red Ram, 1953 to 1954, 3.4375-inch bore x 3.25-inch stroke, 241ci
* Dodge Red Ram and Super Red Ram, 1955 to 1957, 3.625-inch bore x 3.250-inch stroke, 270ci
* Dodge Red Ram D-500, 1957 only, 3.690-inch bore x 3.80-inch stroke, 325ci

SECOND-GENERATION HEMI ENGINES: 1964 TO 1971

* Dodge / Plymouth Race Hemi, 1964 to 1965, 4.250-inch bore x 3.75-inch stroke, 426ci
* Dodge / Plymouth Street Hemi, 1966 to 1971, 4.250-inch bore x 3.75-inch stroke, 426ci

THIRD-GENERATION HEMI ENGINES: 2003 TO PRESENT

* Dodge / Chrysler / Ram (Version 1), 2003 to 2008, 3.917-inch bore x 3.578-inch stroke, 345ci
* SRT 6.1L (Dodge / Chrysler SRT8), 2005 to 2010, 4.055-inch bore x 3.579-inch stroke, 370ci
* Dodge/ Chrysler / Ram / Jeep (Version 2 "Eagle"), 2009 to present, 3.917-inch bore x 3.578-inch stroke, 345ci
* Dodge / Chrysler / Ram / Jeep "Apache" 6.4L, 2011 to present, 4.09-inch bore x 3.72-inch stroke, 392ci
* SRT "Hellcat" 6.2L, 2015 to present, 4.09-inch bore x 3.578-inch stroke, 370ci
* SRT "Demon" 6.2L (Redeye, Demon, Super Stock), 2018 to present, 4.09-inch bore x 3.578-inch stroke, 370ci
#Mopar #HEMI #Chrysler #Dodge #DeSoto #Plymouth #Ram #Jeep #SRT
#FirePower #FireDome #RedRam #Hellcat #Redeye #Demon #SuperStock
Scott Moseman
http://www.TheHEMI.com/
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