be, production or racing, you need an complete engine assembly. It could be stock or modified, fuel injected (as shown) or carbureted, vertical throttle body (shown) or horizontal (most non-truck production units). The parts are readily available to switch the engine in any of these directions.
CHAPTER 1
THE GEN III HEMI
The Hemi story begins with a military aircraft project in 1944–1945 called the Xi2220. This V-16 engine was designed and developed by Chrysler engineers and produced more than 2,500 hp in 1945. That’s just above 1.1 hp/ci. A few years after the end of World War II, Chrysler engineers were asked to design a new production engine, and they selected the Hemi head.
Chrysler introduced the new 331 Hemi production engine in 1951. DeSoto and Dodge soon followed with their own smaller versions of the Hemi. After the 331’s introduction, Chrysler launched larger versions of the new engine with the release of the 354 and the 392. The 392 was the first engine that could be raced on alcohol and nitromethane fuels with a supercharger and survive. The production of the 392-Hemi family ceased in 1958. These three Hemi engines (the 331, 354, and 392) made up the Gen I branch in the family tree. However, it did not receive this nickname until the early 2000s.
The next member of the Hemi family was introduced in 1964 as the soon-to-be famous 426 Hemi. Tom Hoover and his design and engineering team created the 426 based on Chrysler’s big-block wedge engine called the B engine or, more specifically, the RB engine. This big-block had been in production since 1958 and replaced the 392. The 426 Hemi was rated at 425 hp, and it was produced through 1971.
The 426 Gen II Hemi has a tall block, thick valve cover, and tall height to the top of the air cleaner, which results in a wide overall assembly. This is true of all the 1964–1971 Hemis, including race, street, and the few 4-barrels. (Photo Courtesy FCA US LLC)
In eight years of production, Chrysler built 10,669 of the Gen II 426 Hemi engines. The Chrysler 426 engine was brought back by Mopar Performance in 1995/1996, first as parts and then as a crate engine copy of the original 426.
The next generation of Hemi engines was introduced in 2003. The 5.7L engine was the first of the Gen III Hemis. It was followed by three more displacements: the 6.1L, the 6.4L, and the 6.2L. Today, three of the four are still in production, as the 6.1L production ended in 2010.
All of the Gen III Hemi engines are V-8 and feature twin-plug heads, a feature first developed for the Gen II 426 Hemi in the early 1970s. These production engines feature cast-iron blocks and aluminum heads with wide plastic valve covers (black), a beer-barrel shaped intake manifold, multi-point injection (MPI), and a serpentine-belt front accessory drive. In the 14 years of production of the Gen III Hemi engines, there have been approximately 3.8 million engines/vehicles produced. From 2011 to 2017, nearly 130,000 6.4L 392 engines have been built, which is 9.1 percent of production per year or about 30,000 per year at current levels. Currently, the Hellcat and Demon are limited-production options that are restricted to a few thousand per year.
Most of the Gen III Hemi engine assemblies tend to look alike, similar to this Mopar Performance complete 426 crate motor assembly. The direct-mount individual coils bolt to the valve cover and hide the dual-plug feature. The large 4-barrel throttle body on top of the manifold is somewhat unique. It is hard to tell that it has an aluminum block. A stock 6.1L Hemi is shown at the beginning of chapter 2.
Hemi Engine Names
Typical of most large engine projects, the newer Gen III engines were given official code names that became the common nicknames for a particular hardware package. The first three are named after airplanes: the 5.7L Eagle, the 6.4L Apache, and the 6.2L Hellcat. The fourth is the Demon. The 5.7L Eagle is rated at 375/390 hp (up from the original 345 hp) and was introduced in 2009. The 6.4L 392 Apache is rated at 485 hp and was introduced in 2011. The 6.2L Hellcat is rated at 707 hp and was introduced in 2014 as Chrysler’s first supercharged engine. The Demon was introduced in 2017 and is rated at 840 hp.
Of the four production displacements that have been used in the 14 years of Gen III Hemi production, the most popular or most common based on volume is the 5.7L. It has been produced the entire production run, and it has been installed in cars, trucks, and SUVs. The next most popular based on volume is the 6.4L 392. It is one of the newer versions and has just recently been added to the truck line (called the Big Gas) and to the SUV line (as an SRT8 model).
Additionally three nonproduction (racing) displacements are offered: the 354, 362, and 426. The 354 is a supercharged Gen III Hemi used only in the Challenger Drag Pak for drag racing. While similar to the production Hellcat, it has features unique for racing. The 362 is a circle track (Canadian series) engine and is available in crate engine form from Prefix. The Gen III 426 is an aluminum-block version that is used in the Challenger Drag Pak naturally aspirated models (also available from Prefix).
Production Engines
By the 2017 model year, more than 3.8 million Gen III Hemis had been produced. That’s a lot of engine assemblies! Compare this huge number to approximately 10,000 426 Gen II Hemis that were built during eight years of production and about 120,000 units of the 6.4L 392 that Chrysler has built during its seven years of production.
While the newer engines have project nicknames such as Eagle and Apache, only the Hellcat and Demon (shown) have on-car logos.
The original Gen I 392 was introduced in 1957–1958 at 325 to 345 hp with the high-performance version (the 300D) around 1 hp/ci and 380 hp. The 5.7L 345-ci Hemi of 2003 rated at 345 hp, and the Eagle package, introduced in 2009, increased horsepower to around 366 to 390 hp. The newer and larger 6.1L version was rated at 425 hp, which matches the original Street Hemi Gen II power rating in 1966–1971 models with 54 fewer cubic inches: 372 versus 426. Keep in mind that the Society of Automobile Engineers’ (SAE) engine/horsepower rating system made it much more difficult to generate 425 hp in 2010 than the rating system in the 1960s.
In 2011, the even larger 6.4L 392 Hemi was rated at 470 hp! All of this was topped in 2014–2015 with the introduction of the 6.2L Hellcat supercharged engine, which was rated at 707 hp. It was Chrysler’s first supercharged engine and the highest horsepower rating of any production engine through 2016. The 2017 Demon moved the goalpost again with an overwhelming 840 hp!
The 5.7L Engine
The 5.7L 345-ci engine was just slightly larger than the 1968–1973 340 A-engine performance small-block. It used a 3.917-inch bore, which was sometimes rounded up to 3.92 inches. The 5.7L has a stroke of 3.58 inches, similar to the 360 and 5.9L small-blocks that are bigger versions of the 340. The original power rating for the 5.7L was 345 hp in 2003. This rating yields a 1 hp/ci factor, which is excellent for any V-8 production engine, especially bigger V-8s. The original Gen II Hemi was 1 hp under at 425 hp from 426 ci.
The original 5.7L engine was produced from 2003 to 2008, and the 5.7L Eagle was introduced in 2009 and still produced today. The high-performance Eagle package was based on a new high-flow cylinder head with larger ports and bigger valves. The Eagle intake valves were 2.05 inches compared to the standard 2 inches. The valves were also about 0.300-inch longer and the installed height was increased to 1.99 inches, up from 1.81 inches. The bigger ports and bigger intake valves allowed the Eagle intake ports to flow about 40 cfm
