New Hemi Engines 2003-Present. Larry Shepard

“build over.” You might say that it means that you take it apart and put it back together again. Close but not quite! Actually, you take a used engine assembly apart, replace the worn parts, and put it back together again. There are a lot of shades of gray to this sentence, and I will try to cover as many as possible while trying to keep the goal of rebuilding the engine in focus.

       Because the Gen III Hemi is shorter, narrower, and much lighter than earlier Hemis, it makes a great engine swap choice (an A-body shown). The close shock towers presented a problem for the Gen II Hemi and RB big-blocks. (Photo Courtesy Bob Wilson)

      The special features of the Gen III engines (active intake manifold, multi-displacement system, and variable valve timing) are not the main focus of this book, but I will discuss them in general terms so that you can understand what it is and how to remove and install the unique hardware.

      One of the special features of all Gen III Hemi production engines is multi-point injection (MPI). The basic MPI system was introduced on the 4-cylinder engines (2.2 turbo) in 1984 and was on all of the production vehicles with the introduction of the 1992–1993 Magnum V-8 engines (5.2L and 5.9L). One of the key tech features of all MPI systems is the group of 10 sensors that feed engine information to the engine’s computer. It is very important that you become familiar with where these sensors are and what they do. Most of these sensors will be disconnected at engine removal and must be reconnected when the rebuilt engine is reinstalled. Most of these sensors do not have to be removed from the engine part that they are installed in (the throttle body has three, the intake has one, etc.), but the one installed in the block (crank position sensor) must be removed once the engine is on the stand. If not, it could be damaged in all the machining operations that the block goes through.

       With the valve cover removed, it is easy to see the dual-plug towers or stands. The intake (upper) and exhaust (lower) rocker shafts are also visible, along with the highly angled rocker arms.

       The Gen III Hemi engines feature tuned intake manifolds. Tuned intakes were first developed on the late 1950s big-block wedges and the original Gen II 426. These early versions tended to have multiple carbs. The longer runners in the Gen III are accomplished by curling the runner over to create a beer-barrel shape. Note that the runner enters the head at a perfect flow line to match the intake port. The 6.1L Hemi is shown with its aluminum intake; the 5.7L and 6.4L use similar plastic intakes. (Photo Courtesy FCA US LLC)

      When rebuilding, you will want to follow the advice of Hemi specialists. You could define a specialist as an expert on a particular engine family, in that he or she builds lots of them, or has been doing it for years, or, in many cases, all of the above. Engine builders or engine specialists generally are divided into General Motors, Ford, and Chrysler specialties. The Chrysler specialists are often divided further into Hemi engine builders, A small-block engine builders, and RB and B big-block builders. The Gen III Hemi engines are creating their own specialists to add into this mix.

      These engine specialists also develop products to take performance a step or two further. The aftermarket’s role in the basic Gen III Hemi engine development is just beginning, but there are already many options for hardware for your rebuild. With the factory hot rods at 707 hp (Hellcat) and 840 hp (Demon), the naturally aspirated versions will not be far behind as parts and performance packages become readily available. The maintenance and service sides of the aftermarket have been readily available since the introduction of this new engine family, so parts availability should not be an issue with any Gen III Hemi rebuild project. I will address as many of them as I can throughout our rebuilding process.

       No matter what the end project is going to 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