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 more than the standard 5.7L. The Eagle version also makes about 30 to 45 hp more (366 to 390) than the original.
Engine Specifications
Each engine discussed is defined by a specific group of specifications. In addition, Chrysler built these engines in specific model years. In general, the 5.7L and the 6.1L are the oldest and most likely to be rebuilt at this time. The Demon Hemi uses a bigger supercharger than the Hellcat and uses more boost pressure to gain the extra horsepower. Its basic specs are the same as 6.2L Hellcat.
Racing Specs
The three nonproduction engines (354, 362, and 426) were originally built as racing engines. However, they were designed as crate engines that could be retuned for street or dual purpose usage by the manufacturers. These nonproduction engines were offered through the Mopar Performance program and its related Drag Pak program. Today, Prefix and many engine builders offer them. The original 354 Drag Pak engine used a cast-iron block, but the aluminum block used in the 362 and the 426 is now optional at the original bore size. ■
This cutaway of the 392 Gen III Hemi shows the internals of the production engine, also called a 6.4L. Except for the intake system, it is similar to the 6.2L Hellcat/Demon supercharged engines. (Photo Courtesy FCA US LLC)
Because of these changes, swapping parts from the new 5.7L Eagle to the original 5.7L does not work. Rebuilds must use basic service parts for the engine being rebuilt. There are some exceptions, which I’ll discuss in future chapters.
The 6.1L Engine
The 6.1L 372-ci Hemi engine was introduced in 2006 and was produced through 2011. It was a big-bore version of the 5.7L with a 4.055-inch bore that was sometimes rounded up to 4.06 inches. This bigger engine had a different block casting but shared the 3.58-inch stroke with the 5.7L. It was originally rated at 425 hp or 1.14 hp/ci.
The 6.1L’s 2.075-inch valves were slightly larger than the 2.05-inch valves of the 5.7L Eagle, but they were much larger than the original 5.7L’s 2.00-inch valves. The valves are slightly longer and the installed spring height is slightly higher (1.87 inches versus 1.81 inches).
The key to this engine’s performance package is the much bigger camshaft. The 6.1L’s valve lift increased almost 0.100 inch more than the 5.7L standard and Eagle cams, going from 0.472-inch to 0.571 inch lift and 0.460 inch versus 0.551 inch on the exhaust. The advertised duration picked up about 20 degrees, showing 260 versus 283. At 0.571-inch valve lift, this has to be one of the highest lift cams ever used in a production engine. The previous high-lift, high-performance production engine cams of the muscle era (426 Hemi, the 340, the 440-6, etc.) used cams with production lifts around 0.450 to 0.475 inch. High-performance aftermarket cams for these engines tended to peak at around 0.510 inch. The 0.571-inch lift was impressive for production, street, warranty, and emissions considerations! The 6.1L engine was the only V-8 engine in the SRT models in this era.
The 6.4L 392 Engine
The 6.4L 392-ci version of the Gen III Hemi engine had somewhat of an identity crisis. It was originally called the 392, then production called it the 6.4L, and then it was back to the 392. It is the same displacement either way. In the last couple of years, production seems to have settled on 392.
This 392 engine package is also called the Apache. It is rated at 470 hp (2011) or 490 hp (2016–2017), which is 1.20 hp/ci. It has the largest valves to date from the production Gen III Hemi engines with 2.138-inch intakes and 1.654-inch exhausts. It also features the raised valvetrain with the tallest installed spring heights at 2.051-inch intake and 2.016-inch exhaust.
The big port Apache head flows almost 340 cfm. The beer-barrel shaped intake manifold is lightweight plastic and features an angled, single-inlet throttle body mount. It also has variable valve timing (VVT). One interesting feature of the Gen III Hemi engines was that they all had windage trays that were designed as part of the oil pan gasket rather than as three pieces with a separate tray and an oil pan gasket on top and bottom.
The 6.2 Supercharged Hellcat/Demon
The