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 Hellcat was introduced in 2014–2015 and became Chrysler’s first supercharged engine. The Hellcat engine was similar to the 6.1L and 6.4L Hemis. It used a cast-iron block with a 4.09-inch bore, which was the same as the 6.4L 392. It also used the 6.1L’s 3.58-inch stroke. This made the engine a 6.2L version at 378 ci. The engine was rated at 707 hp and 650 ft-lbs of torque, the highest horsepower rating for any production engine. The Hellcat blocks were painted orange.
The Hellcat used a similar cam as the 392 with a 0.571-inch lift, but it had 8 degrees fewer intake duration and 16 degrees more exhaust duration. The twin-screw supercharger was built by IHI Turbo America and displaced 2,380 cc. The boost pressure was electronically regulated to 11.6 psi. The supercharger was driven by the serpentine drive belt and the aluminum heads used smaller valves than the 392 engine. It maintained the long valves and tall installed height.
When the Hellcat was introduced, no one thought that this production output level could be matched because racing and custom builds have unique emissions and warranty situations that relate to production engines. Many felt that if it was going to be topped, it would only be by 10 or 20 hp. That held true for a couple years, and then the 2017 Demon burst on the scene with 840 hp! The Demon uses the same basic 6.2L engine as the Hellcat, but the supercharger is larger on the Demon at 2,900 cc and 14 psi boost pressure compared to the Hellcat’s 2,380 cc with 11.8 psi.
The dual-plug feature of all Gen III Hemi engines is easier to see with the valve cover removed. The tops of the twin spark plug towers for each cylinder look like a figure-8 on its side. You can also observe the two rocker shafts (intake at the top), which are a feature of the Hemi-head design.
Family Identification
The quick and easy way to distinguish the Gen I Hemi engines from the Gen II engines was to look at the distributor. The Gen I had the distributor at the rear, while the Gen II had the distributor at the front. This can be seen even in the bare blocks. The Gen III doesn’t use a distributor, but this isn’t obvious at first glance.
If you are used to looking at bare Gen II Hemi blocks, a bare Gen III Hemi block will most likely look small. Based on the block’s bore centers, it is actually the size of a small-block. In its normal position, the block’s pan rails sit square to the floor because of the skirted design. The most unique feature of the Gen III Hemi V-8 bare block is the high-point in the center of the front face. This high point is created by the intersection of the two deck surfaces of the bare block. The front face creates the shape of a capital A. It is lovingly called the bird house. This A shape is not carried to the rear face.
If the engine is assembled, the A shape of the front face is now located behind the front cover, water pump, and all, making it more difficult to see. When assembled, perhaps the most obvious features of the Gen III Hemi are the dual spark plugs for each cylinder and the valve cover is wider than the traditional wedge-head valve cover. All of the production Gen III engines use a beer-barrel shaped intake manifold, and all Gen III Hemi engines use a serpentine front accessory drive. These last two features are not unique to the Gen III Hemi; they were also shared with the earlier 1992–2003 Magnum engines, so they are not as good to use
