Chrysler Hemi engine

The main advantage of a hemispherical head engine over other head designs is power. On the other hand, hemi head engines tend to have complex valve trains, are expensive to build, and are larger and heavier than conventional designs. A hemispherical combustion chamber is efficient, with an excellent surface-to-volume ratio, and room for two large valves. However, it allows no more than two valves per cylinder because of their large size, and they are necessarily heavier than those in a multi-valve engine. The intake and exhaust valves lie on opposite sides of the chamber and necessitate a "cross-flow" head design. Because the combustion chamber is a partial hemisphere, a flat-topped piston would yield a low compression ratio unless a very long stroke is used. The piston crown is domed to protrude into the head at top dead center to attain the desired compression ratio. The result is a combustion chamber in the shape of the space between where the domed piston stops and the dome shape in the head receiving it. The hemi-head design places the spark plug at or near the chamber's center to promote a strong flame front. However, if the hemi-head hemisphere is of equal diameter to the piston, there is minimal squish for proper turbulence to mix fuel and air thoroughly. Thus, hemi-heads, because of their lack of squish, are more sensitive to fuel octane rating; a given compression ratio will require a higher octane rating to avoid detonation in a hemi engine than in some conventional engine designs, such as the wedge and bathtub. The hemi head always has intake and exhaust valve stems that point in different directions, requiring a large, wide cylinder head and complex rocker arm geometry in both cam-in-block and single overhead cam engines (dual overhead cam engines may not have rocker arms). This adds to the overall width of the engine, limiting the vehicles in which it can be installed. Significant challenges in the commercialization of engine designs using hemispherical chambers revolved around the valve actuation, specifically how to make it effective, efficient, and reliable at an acceptable cost. This complexity was referenced early in Chrysler's development of their 1950s hemi engine: the head was referred to in company advertising as the Double Rocker Shaft head. Chrysler and Imperial All Chrysler FirePower engines are oversquare; i.e. their bore is larger than their stroke. The 331 engine was used in the following applications: • 1951–1955 Chrysler New Yorker • 1951–1954 Chrysler Imperial and 1955 Imperial • 1951 Chrysler Saratoga • 1952 Chrysler Saratoga Club Coupe • 1952 Chrysler Imperial Parade Phaeton • 1954 Dodge C Series • 1955 Chrysler C-300 • 1956 Facel Vega FV2B • 1958 Hongqi CA72 • The Chrysler Air-Raid Siren. At 138 decibels, it is reputed to be the loudest siren ever made. 354 The 354, released in 1956, had a bore of 3.9375 (100mm) in and stroke of 3.625 (92.1mm) in, and the same 10.385" (264mm) low deck height, for a displacement of . The 300B engine was rated at , while the New Yorker and Imperial 354 engine configuration produced . For the 300B, an optional version was available, making it the first American V8 to be rated at one horsepower per cubic inch. (Note that before 1972, horsepower was SAE gross (equivalent to maximum output); thereafter, it was rated as SAE net (power delivered to the transmission, less accessories, emission controls, exhaust system, and other power-sinks).) The 354 was also modified. The Hemi was optimized for heavy-duty truck service. These were available with one or two four-barrel carburetors, and were offered in Dodge's heaviest-duty models as the 'Power Giant V-8' from 1957 through 1959; they were the largest of four Hemi truck engines offered by Dodge in the 1950s. The 354 was also offered in certain models with polyspheric heads rather than hemi heads. The combustion chambers on these had similarities to both hemi and wedge heads, but were closer in weight to wedge heads. Thus, both 354 poly and 354 Hemi V8 engines were variously available in 1957. The 354 engine was used in the following applications: • 1956 Chrysler New Yorker • 1956 Chrysler 300B • 1956 Imperial Custom & Crown • 1957 Dodge D-501 • 1957–1959 Dodge C Series Pickup 392 The 392 raised-deck engine released in 1957 had a bore and stroke. The actual displacement is . The deck height, at , was taller than that of the previous blocks. Because its deck was taller, the heads were cast with wider intake ports so that earlier manifolds could be used with the new heads on the new taller block. For 1958, Chrysler offered the 392 in two configurations: with 9.25:1 compression and with 10:1 compression, both with a single four-barrel carburetor. A dual four-barrel version of the 392 available in the 1957–58 Chrysler 300C and 300D cars was rated at ; the 300D, and some marine and industrial engines, used a (now rare) adjustable rocker. An extremely rare option available on the 1958 300D was Bendix "Electrojector" fuel injection, with which the 392 was rated at . Due to reliability problems with the primitive onboard computer which controlled the injection system; however, 15 of the 16 300D cars built with the fuel injection option were recalled and retrofitted with carburetors. The 392 engine was used in the following applications: • 1957–1958 Chrysler New Yorker • 1957–1958 Imperial Custom, Crown, and LeBaron • 1957 Chrysler 300C • 1958 Chrysler 300D • 1958 Facel Vega Excellence (EX) In the late 1950s and early 1960s, drag racers found the 392 to be a formidable engine and continued to run them competitively into the 1970s. Usual color of the block was silver. Dodge did not have a V8 engine until one was developed specifically for the line in 1953 based on the 1951 Chrysler hemi design, but downsized for these smaller cars. They have the smallest bore center spacing of any hemi engine at . They do not share any major dimensions or components with the larger Chrysler and DeSoto hemi engines, or the Plymouth A engines. From 1955 to 1958 (see 1956 D500 Dodge D-500 cars and packages: early performance cars) lower-performance Hemi-based alternatives to the Dodge hemi were introduced by substituting less complex poly (single rocker shaft) heads and valve train parts, including one variant only built as a poly (259"). These were used in low-line 1955-58 DeSotos and Dodges, and 1955-56 high-line Plymouths. Dodge Trucks marketed their version of the Hemi under the name PowerDome. 241 Dodge introduced the engine in 1953. For 1954, the more senior Dodges received a higher 7.5:1 compression ratio version. This engine is not the same as the Plymouth 241, which had polyspheric heads. The 241 Dodge Hemi only lasted two years, being replaced by the 270 for 1955. 315 For 1956, Dodge increased the displacement to with a longer stroke and a taller raised-deck block, but used polyspheric rather than hemi heads on the base version. The optional high-performance D-500 version had a four-barrel carburetor and a larger-valved Dodge hemispherical combustion chambered head. Also, a "race only" package called the D-500-1 or DASH 1 was available with a special aluminum dual four-barrel intake that sported a pair of Carter WCFB carburetors similar to the ones on the Chrysler 300B and DeSoto Adventurer. This engine used the same cylinder heads as the base D-500 model. In 1957 the D-501 was the Chrysler 354 engine, not a Dodge-based engine. 325 Dodge released the "Super Red Ram" engine for 1957. It used a bore and stroke, and a polyspheric chambered head (referenced as 'KDS') in its base version. A higher performance 325 was offered with hemi heads as the 'KD-500'. The 'KD-500-1' came with dual four-barrel carburetors. Even though the hemi headed offerings sported "dimples" in the valve covers for mechanical adjuster clearance, all engines had hydraulic lifters. == Second generation: 426 1964–1971==

Chrysler’s development program, 1962–66 In a 1967 professional journal, Chrysler laid out in full detail the chronology and particulars of the new hemi engine’s development: “In December 1962 a request was made of engineering staff to develop an engine and vehicle combination capable of winning stock car competitive closed circuit track events throughout the country. It was further requested that a version of the engine suitable for use in supervised timed vehicle acceleration drag events also be made part of the engine portion of this program. Both of these applications were to share the same basic design and development; thus a decision on the basic engine itself was one that required careful consideration. However, the decision for Chrysler was obvious. The hemi engine had been a production engine from 1950 until it was discontinued in 1958. The background of development that preceded the production version of the engine was available, as was experience in converting the engine for competition use. Chrysler hemi engines had been used previously in track events, and were still in use in many drag events….The design of the new hemi engine began in January 1963 with the Feb. 23, 1964 Daytona Beach, Fla. race set as the first target date. A number of engine design avenues were initially explored in order to gain as many performance and durability features as possible while still retaining much of the existing [production] cylinder block tooling as practical. The final design selected was deemed to have the potential necessary to win and the program was launched. The engine requirements were to include a single 4 barrel carbuetor 426 cu in. track engine, and single barrel carburetor 396 cu in. track engine and a two 4 barrel carburetor 426 cu in. drag engine. Immediately following the initial introduction of the engine, a production run of several hundred drag engines and cars were planned to be built. This would serve to give widespread usage of the hemi on drag strips throughout the country and also serve as production backup to the track engine." The article continued: "Experimental procurement of the 426 cu in. hemi engine was started in July 1963 and was completed by the end of November. The first engine ran under its own power on Dec. 6 1963. This engine was built as a track engine; the drag engine version was built later the same month. The 396 cu in. track engine had subsequently been removed from the rules and the engine was never built. This 426 cu in. track engine was used extensively throughout the 1964 season. The production of several hundred drag engines was completed by the end of the 1964 model year. Another production run of several hundred drag engines was made for the 1965 model year automobiles, with a considerable weight decrease for the engines obtained by the usage was restricted due to a change in eligibility rules which limited the scheduled race events in which the hemi engine was allowed to compete. A detuned high volume street version of the 426 hemi was designed, developed, eleased, and tooled as part of the 1966 model offering…With this release, full eligibility of the engine for 1966 track use was again established. A 404 cu in. version for use on certain tracks was also prepared for the 1966 season in complicance with the revised racing rules.” Specifications The 1960s 426 was the first engine called "Hemi" by Chrysler, the 426 was nicknamed the "elephant engine" at the time, a reference to its high power, heavy weight, and large physical dimensions. Its deck height and bore spacing made it the biggest engine in racing at the time. The 426 Hemi "Track" version, produced for use in NASCAR, was raced in a Plymouth Belvedere in 1964 by drivers such as Richard Petty. It was not initially available to the general public. Complaints by Ford regarding its power led to the "Race Hemi" being banned from NASCAR's 1965 season due to its unavailability in production vehicles. However, several special homologated production versions of the Dodge Dart, the Plymouth Fury, and later, in 1965, the Dodge Coronet, were produced with aluminum fenders and bumpers for drag racing and made available to the general public. Chrysler introduced the "Street Hemi" in 1966 for its intermediate range of cars and sold the required number of Hemi engines to the public to homologate its use for stock car racing in NASCAR events in 1966. The detuned “Street” engine differed from the “Track” and “Drag” versions in many ways: lowered compression (from 12.5 to 10.25), bearing cap material (cast iron rather than malleable iron), a different finish on the crankshaft journals, piston weights, piston clearance, piston pin size, valve springs and intake manifold design. The “Street” engine featured a heated intake manifold, cast iron exhaust manifolds, automatic choke, and a milder cam. In actual dynamometer testing, it produced and of torque in purely stock form. Chrysler's sales literature published both the gross and net ratings for 1971. The “Track” and “Drag” engines were more alike than the “Street” engine was with either. Among differening specifications in these racing engines for 1964-66 were: piston weights, intake valve diameter, water pumps, carburetion, camshaft profiles, and construction material (more aluminum and magnesium in “Drag” engine). and a different head bolt pattern. Although all manufacturers were familiar with multi-valve engines and hemispherical combustion chambers, adding more valves per cylinder and designing the complex valvetrain they require were expensive ways of improving the high–revolutions per minute (rpm) breathing of production vehicles. By canting the angle of the NASCAR-mandated two valves per cylinder, significantly larger valves could be used. Both the Chrysler 426 Hemi and all Chrysler RB engines were oversquare, with the 426 Hemi and 426 Wedge sharing a bore and stroke. Blocks for the 426 Hemi were stress relieved at the factory, to prevent cracking under high RPM loads. • Valvetrain and Camshafts: The valvetrain and camshafts on the street engine were way different from those used on the racing Hemis. The street engine had hydraulic lifters to damp out the noises and leaks that would otherwise be common. The racing engine had a very aggressive mechanical cam, and solid-lifter ramped camshafts to keep the valves from floating on the shoulders at the high RPMs (Mueller, 2013, p. 155). • Induction and Exhaust: As delivered by the factory, all street engines came with a dual four-barrel, inline, cast iron intake. On most racing applications the Cross-Ram induction system was used. The Cross-Ram featured the four barrels installed offset from each other with longer runner lengths to improve airflow (Mueller, 2013, p. 154). ==Third generation: 2003–present ==

The current-production "HEMI" engine heads are flatter and more complex than the 1950s–'70s Hemi V8 chamber. The combustion chambers are no longer truly hemispherical. It uses a coil-on-plug (distributor-less) ignition system and two spark plugs per cylinder to shorten flame travel leading to more consistent combustion and reduced emissions. Like most of Chrysler's past-model Hemi-head engines, the 5.7 L version is rated at approximately one horsepower per cubic inch (the current engines are SAE net, whereas the old Hemi engines were rated SAE gross). For the 2009 model year power was increased to 357-395 horsepower (266-291 kW) and 389-410 lb·ft (527-556 N·m) depending on application. It also achieved 4% better fuel economy. Variable valve timing (VVT) was also introduced. A new variable displacement technology called Multi-Displacement System (MDS) is used in some versions which can shut off two cylinders on each bank under light load to improve fuel economy. 5.7 The 5.7 L HEMI was released for model year 2003 on the Dodge Ram pickup trucks to supplant the Magnum 5.9 engine. From 2004 to 2013, it was the only available gasoline engine in the Ram Heavy Duty. Chrysler later made the 5.7 L Hemi available in all models of the 2004 Dodge Ram, Dodge Durango, the 2005 Chrysler 300C, Dodge Magnum R/T, Jeep Grand Cherokee, the 2006 Dodge Charger R/T, Jeep Commander, the 2007 Chrysler Aspen, the 2009 Dodge Challenger R/T, and the 2022 Jeep Wagoneer. For manual transmission applications (Challenger and 3/4- and 1-ton Ram pickups), cylinder deactivation is not included. The Hemi in the Ram delivered and , but and for the 300C and Magnum R/T, which is exactly more than the old 5.9 engine. It is a 90-degree V8, 2-valve pushrod design like the past Magnum series engines, displacing , with a bore of and a stroke of . The 5.7 L Hemi is made at Chrysler's Saltillo Engine plant in Ramos Arizpe, Mexico. The Hemi was on the Ward's 10 Best Engines list for 2003 through 2007, and again in 2009. This engine has been used in the following vehicles: • 2003–present Ram 1500 • 2004–present Dodge Durango • 2005–2008 Dodge Magnum R/T • 2005–2021 Chrysler 300C • 2010, 2012–2023 Chrysler 300S V8 • 2005–2023 Jeep Grand Cherokee • 2006–2023 Dodge Charger R/T • 2006–2010 Jeep Commander • 2007–2009 Chrysler Aspen • 2009–2023 Dodge Challenger R/T • 2022–2023 Jeep Wagoneer 2009 VCT Revision Chrysler made various revisions to the 5.7 L for the 2009 model year. The first for all applications was what Chrysler called Variable Camshaft Timing or VCT. VCT (which is essentially variable valve timing) uses an oil control valve that controls oil flow to a unique camshaft sprocket that contains a phasing device, which depending on the operation of the oil control valve, either advances or retards camshaft timing. Cylinder heads were revised to increase flow. Though the intake manifold was also changed on all applications, it was still model-specific. The Dodge Ram, non-Hybrid Electric Vehicle (HEV) Chrysler Aspens, and non-HEV Dodge Durango utilized an active intake manifold with a short runner valve to optimize torque and horsepower. At lower engine speeds, the valve was closed, resulting in improved low-end torque from the longer runners. At higher engine speeds, the valve was opened, diverting the incoming air into the center of the manifold. The shorter runners resulted in improved horsepower. Passenger cars, Jeep vehicles, as well as HEV Chrysler Aspen and HEV Dodge Durango did not use this manifold; instead, these vehicles utilized a passive intake manifold, which did not have a short runner valve. Also, the new cylinder head came with different spark plug seats: tapered seats were replaced with gasket seats. This change made it impossible to use the old OE Champion RE14MCC4, so the new spark plugs that came with 5.7 HEMI became NGK LZFR5C-11. Besides different seats, the spark plug gap grew from .039" (1.0 mm) to .043" (1.1 mm). Engines mated to the six-speed manual transmission or used in the Ram Heavy Duty did not feature the Multi-Displacement System (MDS). The new version of the 5.7 L had five different camshaft profiles, all with VCT: • Active intake without MDS • Active intake with MDS • Passive intake without MDS • Passive intake with MDS • HEV application (modified version of passive intake with MDS) Power numbers: • 300C/300S V8: , • Charger R/T: , • Challenger R/T automatic: , • Challenger R/T 6-speed manual: , • 2009–2012 Ram 1500 truck: , • 2013+ Ram 1500 truck: , • Ram 2500/3500 truck: , • Jeep Grand Cherokee and Jeep Commander: , • 2011+ Dodge Durango: , • 2009 Chrysler Aspen and Dodge Durango non-HEV: , • 2009 Chrysler Aspen and Dodge Durango HEV: , • 2022 Jeep Wagoneer: , 6.1 The Hemi was also available in a version that was developed in 2004 for the 2005 Model Year Chrysler 300C SRT8. The engine's bore × stroke was , and many other changes were made to allow it to produce at 6,200 rpm and of torque at 4,800 rpm. The engine block differed from the 5.7, with revised coolant channels and oil jets to cool the pistons. A forged crankshaft, lighter pistons, and strengthened connecting rods improved durability. A cast aluminium intake manifold was tuned for high-rpm power and did not include variable-length technology. Chrysler's Multi-Displacement System was not used on the 6.1. Applications: • 2005–2010 Chrysler 300C SRT-8 • 2006–2008 Dodge Magnum SRT-8 • 2006–2010 Dodge Charger SRT-8 • 2006–2010 Jeep Grand Cherokee SRT-8 • 2008–2010 Dodge Challenger SRT-8 6.2L Supercharged HEMI (SRT Hellcat) For 2015, Chrysler introduced an all-new high performance supercharged variant of the Hemi engine, called the Hellcat (named after the Grumman F6F Hellcat). This engine was the most powerful engine produced by Chrysler as well as the most powerful production engine ever in a muscle car until the Dodge Demon was introduced. In 2017, Mopar announced that it would sell it as a crate engine under the name Hellcrate. A Redeye version with debuted in the Dodge Challenger in 2019, followed by the Dodge Charger in 2021. Applications: • 2015–2023 Dodge Challenger SRT Hellcat/Hellcat Redeye • 2015–2023 Dodge Charger SRT Hellcat/Hellcat Redeye • 2018–2021 Jeep Grand Cherokee Trackhawk • 2021, 2023–present Dodge Durango SRT Hellcat • 2021–2024, 2026–present Ram 1500 TRX SRT Demon The Demon version of the Hemi V8 features a number of improvements over the Hellcat variant. It is fitted with a larger, 2.7 L twin-screw supercharger, as well as reinforced reciprocating components, a new camshaft, and several other valvetrain upgrades. With these improvements, the Challenger SRT Demon is rated at on 91-octane pump gasoline, and 840 horsepower when running on 100-octane unleaded racing gasoline. Cooling is aided by a functional Air-Grabber hood scoop, as well as a unique charge cooling system that makes use of the air-conditioning coolant to lower the intake charge air temperature. Applications: • 2018 Dodge Challenger SRT Demon 6.4 Chrysler displayed a larger and more powerful 392-cubic-inch (6.4 L) HEMI in 2005 with a factory-rated output of and torque. It is equipped with high-strength forged aluminum alloy pistons. This engine has been available since 2007, as a crate engine under the name 392 HEMI. The new 392 HEMI, codenamed "Apache," is based on the third-generation 5.7 L HEMI, codenamed "Eagle," and shares few parts with the 392 crate engine. The "Apache" 6.4L features forged steel crankshaft, hypereutectic cast aluminum pistons with floating pins, 10.9:1 compression ratio, 2.14in intake valves and 1.65in exhaust valves. Special-edition Chargers and Challengers equipped with this engine, and the engines themselves, featured "392 HEMI" badging in commemorative reference to the first-generation engine of the same displacement. In other applications, the engine is badged as "6.4L HEMI." Output is and ; For the 2015 model year, horsepower was increased to and torque to in the Charger and Challenger SRT 392 (2015–2018) and R/T Scat Pack (2015–2023) models; the Grand Cherokee SRT only saw a 5 bhp increase. Export models of the Chrysler 300 SRT retained the and output. Applications: • 2023 Chrysler 300C • 2012–2014 Chrysler 300 SRT-8 • 2015–2021 Chrysler 300 SRT (Overseas) • 2011–2023 Dodge Challenger SRT-8/SRT 392/Scat Pack • 2012–2023 Dodge Charger SRT-8/SRT 392/Scat Pack • 2018–2024 Dodge Durango SRT • 2012–2021 Jeep Grand Cherokee SRT-8/SRT • 2022–2023 Jeep Grand Wagoneer • 2021–2025 Jeep Wrangler Unlimited Rubicon 392 • 2025—present Jeep Wrangler Moab 392 • 2026—present Jeep Wrangler Willys 392 • 2026 Dodge Durango R/T Ram Heavy Duty truck and chassis-cab version Starting in model year 2014, the Ram 2500 and 3500 trucks, and Ram 3500, 4500, and 5500 chassis-cabs offered a revised version of the 6.4 L known as the "BGE", Big Gas Engine. Compared to the 6.4L in passenger cars/SUVs, the truck version is tuned for durability and a power band more suitable for hauling and towing, and compatibility with lower octane fuel. The BGE 6.4L features a grey cast iron block shared with the 6.2L Hellcat engine, which features reinforced bulkheads and ribs. The aluminum heads of the BGE 6.4L are also shared with the Hellcat 6.2, manufactured with additional ribs and cast from 356-T6 aluminum. The BGE 6.4L features dished pistons to achieve a lower compression ratio of 10.0:1, vs the 10.9:1 compression ratio of the SRT variant. The engine rpm is limited to 5800rpm in pickup truck models, and 4660rpm when paired to the Aisin transmission. In 2016, it replaced the 5.7 L as the standard gasoline engine in the chassis-cab models, and for 2019 became the standard gasoline engine in 2500 and 3500 models. Power numbers: • Ram 2500/3500 pickup and 3500 SRW chassis-cab with RFE or ZF 8HP transmission: , • Ram 3500 Mega Cab and 3500 DRW chassis-cab with RFE or ZF 8HP transmission, 3500 SRW/DRW with Aisin transmission: , • Ram 4500 and 5500 chassis-cab: , Mopar 426 HEMI (2012–2014) At the 2012 North American International Auto Show in Detroit, Dodge debuted a Mopar Customized Dodge Charger "Redline" that featured a modern HEMI V8 engine rated at . Mopar 426 HEMI 'Hellephant' (2018–present ) The Hellephant name is a spin on the nickname of the original HEMI, Elephant, and the modern Supercharged 6.2-liter Hellcat HEMIs. It is a crate engine, supercharged as standard, producing and of torque. Marketing From February to April 2005, DaimlerChrysler hosted a "What Can You HEMI?" contest promoting alternative uses of the HEMI engines. The top five finalists include HEMI Snowblower, HEMI-Go-Round carousel, "HEMI on Ice" ice resurfacer, HEMI-Shredder, and HEMI Big Wheel (i.e., the child's tricycle of the 1970s). The winner was the HEMI Big Wheel, which had a 5.7 L Hemi in the back that was installed backwards; thus, reverse became the only forward gear. Plate steel was the predominant material, while a rolled tube of steel had to be utilized for the front tire because there were no such tires in diameter that were as narrow as needed for this project. ==Notes==