Chrysler Hemi History: PT 1

Hemis!!!!

As domestic manufacturers fought for engineering supremacy following World War II, Chrysler emerged with unique research produced from an experimental inverted V16 engine with over 2,500 hp & 36 liters of displacement called the IV2220. When mounted to the airframe of a P-47D Thunderbolt, the hemispherical IV2220 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 as jet powered aircraft were the future. Introducing the first production Hemi V8 in 1951 as the Chrysler FirePower V8, then in 1952 in the DeSoto as the FireDome V8, Chrysler was able to leapfrog GM by adding another crucial technological advantage to the overhead-valve formula: the hemispherical combustion chamber.

First-Gen Hemi: The half-spherical combustion chamber was superior to ordinary wedge-chambered heads because of its intrinsic octane tolerance & 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 & exhaust valve rocker arm rails) the valves could open unshrouded into the cylinder, admitting heretofore unobtainable amounts of air & fuel. Armed with this technological advantage, Chrysler & Imperial introduced several Hemi engine sizes, starting with the 331as the FirePower in 1951, the DeSoto 276 FireDome in 1952, & the Dodge 241Red 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, & more compression. Under the Chrysler Corporation umbrella, there wasn’t just one Hemi design, but three, one for each brand in the Chrysler, DeSoto, & Dodge lineup. There would be no Hemi for Plymouth until the second generation in 1964 when the 426 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 1951~1958 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 1957~1958 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 & 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 & size associated with the dual-shaft rocker-arm layout & the engine’s wide berth made polyspherical & wedge chambered single rail valvetrain layouts cheaper & more easily packaged.

Second-Gen 426 Hemi: Before the lights went out on the original Hemi around 1958, Chrysler had approached racing 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, to do tire testing for Goodyear & 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 311 Hemi-equipped Kurtis Kraft machine that ran as fast as that year’s top Indy Miller & 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-gen Hemi debuted for 1964 as a race only option in Dodge & Plymouth machines.

The 426 Race Hemi: Since much of Chrysler’s big block Wedge program had evolved from work done on Hemi engines in the 50s, 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 & Don Moore to develop an engine that could win Daytona, the A311 Indy program was dusted off & 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 426 behemoth dubbed the Race Hemi, & 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. 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 & sat out the 1965 season to concentrate on drag racing.

The 426 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 & Plymouth as the reigning kings of the muscle car world. Tired of seeing Fords everywhere & no fans in the stands, NASCAR finally relented & 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, & heat risers for cold-start drivability were added. At a cost of $900 for the Hemi option, buyers also got suspension & 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 & Plymouth B-Body intermediates also in limited numbers of A-Body Dodge Darts & Plymouth Barracudas for use in drag racing. When Dodge & 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.

The Gen3 Hemi: After the bottom dropped out of the performance world in the early 70s, it would be decades before Chrysler dared entertain the idea of breaking out the Hemi design again. Late to disengage from large cars & large engines, Chrysler found itself burned by its lack of fuel efficient front drive offerings & 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 & GM. To take advantage of the new sales success of performance, Chrysler embarked on the development of a new V8 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 03 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 Ram trucks at first, the new 345-hp Hemi enjoyed good reviews & 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 04 with the introduction of the LX platform passenger cars: the 300C & Magnum R/T. The Charger R/T would come online as a 06 model. At last, the Hemi had come full circle, manifesting itself in the 300C, a car that paid more than a little visual & performance homage to the Hemi powered C-300 of 1955. Behind the doors at Chrysler, the plan was to proliferate Hemi engine sizes & dominate the performance world & the newly formed Street & Racing Technology group was tasked with the job. The 345-hp 5.7-liter Hemi was put on a regime of steroids & weightlifting, emerging at a buff 6.1 liters of displacement & 425 hp. The beefcake 6.1L was an exclusive in SRT’s line of SRT8 LX sedans that comprised the 300C SRT8, the Magnum SRT8, the Charger SRT8, & the 2008 Challenger SRT8.

Gen3 Hemi, V2.0: Chrysler was gearing up for the return of the Challenger R/T for 09 & it gave engineers an opportunity to make a series of mechanical improvements to increase power & fuel economy with the addition of variable camshaft timing (VCT) & multidisplacement system (MDS). Higher-flowing heads bumped power output roughly 30 hp, from around 340 hp to 370+ hp. Called the “Eagle”, the second version of the Gen3 Hemi is currently under the hoods of rear-drive 09 & up Dodge, Ram, Jeep, & Chrysler cars & trucks. At the same time the Eagle Hemi hit the streets, SRT was working on the 392ci, 6.4L “Apache” Hemi in SRT8 versions of the 2011 300C, Charger, & Challenger, all with 485 hp. Further improvements over the V2.0 Eagle Hemi are found in the intake, heads, & cam. In the time since the Apache’s introduction in 2011, it has made the jump to Ram trucks (2014), Durango (2018), & Jeep Wrangler (2011).

Supercharged: Hellcat, Demon, Redeye, & Super Stock: For the 2015 model, Dodge rolled out a series of 700-plus-horsepower Hemis, first with the 6.2-liter Hellcat. Adding an IHI 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, & once introduced in SRT’s Challenger, the 707-hp Hellcat would surface in the Charger (2015), Grand Cherokee Trackhawk (2018), Hellcat Durango (2021), & Ram TRX (2021). The high point of the Hemi came in April 2017 with the 840-hp Demon. Based on the Hellcat Hemi, the 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 race fuel, 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 Demon featured a brace of race-specific hardware, including DOT drag radials, electronically controlled drag suspension, line-lock, a transbrake, wide fender skirts to house the oversized drag tires, & other drag-specific features. Once the 2018 Demon had run its course, SRT followed up with the Widebody Redeye Challenger at 797 hp in 2019 & 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. 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 are identical. In 2020, SRT rolled out another killer machine in the 2020 SRT Super Stock, which is more rare with just 200 built. This time, the Super Stock’s Demon Hemi was rated at 807 hp, versus 808 hp in the Demon & 797 hp in the Redeye.

Hemi Engine Sizes By Year:

1ST GEN HEMIS: 1951~1958:

Chrysler FirePower 331, 51~55 Chrysler & Imperial, 3.8125″ bore x 3.625″ stroke.
Chrysler FirePower 354, 56~57 Chrysler, Imperial & some Dodge trucks 57~59, 3.9375″ bore x 3.625″ stroke.
Chrysler FirePower 392, 57~58 (taller deck by .5 inch, favored by racers), 4.00″ bore x 3.906″ stroke.
DeSoto FireDome 276, 52~54, 3.625″ bore x 3.344″ stroke.
DeSoto FireDome 291, 55 only, 3.72″ bore x 3.344″ stroke.
DeSoto FireDome 330, 56 only, 3.72″ bore x 3.8″ stroke.
DeSoto FireDome & FireFlite 341, 56~57, 3.78″ bore x 3.8″ stroke.
DeSoto FireDome 345, 57 only, 3.8″ bore x 3.8″ stroke.
Dodge Red Ram 241, 53~54, 3.4375″ bore x 3.25″ stroke.
Dodge Red Ram & Super Red Ram 270, 55~57, 3.625″ bore x 3.25″ stroke.
Dodge Red Ram D-500 325, 57 only, 3.69″ bore x 3.8″ stroke.

2ND-GEN HEMI ENGINES: 64~71:

Dodge / Plymouth 426 Race Hemi, 64~65, 4.25″ bore x 3.75″ stroke.
Dodge / Plymouth 426 Street Hemi, 66~71, 4.25″ bore x 3.75″ stroke.

3RD-GEN HEMIS: 03 TO PRESENT:

Dodge/Chrysler/Ram (V1), 03~08, 3.917″ bore x 3.578″ stroke, 345ci
SRT 6.1L Dodge/Chrysler, 05~10, 4.055″ bore x 3.579″ stroke, 370ci
Dodge/Chrysler/Ram/Jeep (V2 “Eagle”), 09 to present, 3.917″ bore x 3.578″ stroke, 345ci
Dodge/Chrysler/Ram/Jeep “Apache” 6.4L, 11 to present, 4.09″ bore x 3.72″ stroke, 392ci
SRT “Hellcat” 6.2L, 15 to present, 4.09″ bore x 3.578″ stroke, 370ci
SRT “Demon” 6.2L, Redeye, Demon, Super Stock, 18 to present, 4.09″ bore x 3.578″ stroke, 370ci

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