New Hemi Engines 2003-Present. Larry Shepard
Hemi” are popular, or two smaller cover versions, such as this “Powered by SRT” version. In this case, the engine’s intake manifold sits between the two covers.
The 2011 Gen III 6.4L 392 makes 1.23 hp/ci on a much tougher rating system based on emissions and fuel economy concerns. The fact that 6.4L 392 produces 485 hp is impressive for an engine that is fully emission certified, has warranties through corporate dealers, and is rated on today’s SAE regulation. It is one of the highest nonsupercharged production engines, especially of this size.
Supercharging
Supercharged engines have been in production at Chrysler since late 2014. The Gen III Hemi with a supercharger spools out some pretty big power numbers, as the 707 hp on the 2014 Hellcat and the 840-hp Demon in 2017 demonstrate. Supercharging the Hemi engine family has produced impressive results ever since the introduction of the Hemi in the 1950s.
Supercharging was popular on the early 354 and 392 Gen I engines in drag racing. These drag racing superchargers were mainly 6-71 and 8-71 blowers driven by a cog-belt off the front of the crank. Supercharging was also popular on the 426 Gen II engines, especially in modified classes such as all drag racing classes (AA/GS), Top Fuel, and Funny Car. By the early to mid-1970s, these Gen II Hemi supercharged engines were available from the aftermarket with aluminum blocks that were copied from the cast-iron production blocks.
The top of the supercharger covers the top-center of the engine in the supercharged versions. Two separate engine covers say “supercharged Hemi.” These covers offer engine customizers a great opportunity to be creative. (Photo Courtesy FCA US LLC)
The production supercharger is driven by a very wide multigroove belt that is similar to the serpentine accessory belt but is almost twice as wide. It is located just behind the radiator hose. At more than 2 inches wide, the green belt is quite obvious.
While the racing evolution of the Gen III Hemi began slowly, it began picking up speed with the introduction of the 426 Drag Pak engine. At 426 ci, it was much larger than the production engines and had an aluminum block and MPI injection with a 4-barrel throttle body that replaced the single-throttle body used in production.
Racing Evolution
In automotive history, manufacturers have often made statements that they use racing to develop better production engines. There is probably no better example of this than the Gen II 426 Hemi built from 1964 through 1971. The 426 racing engine was rebuilt a lot. This constant rebuilding of the basic hardware in a neverending quest for more performance is common in racing. The repeated rebuilding basically wore out these Gen II engines. By the early 1990s, there were also major availability issues, which were resolved in the mid-1990s when Chrysler’s Mopar Performance brought it back.
The Gen III Hemi aluminum block is a direct replacement for the original 5.7L Gen III Hemi engine, with the exception of the bore size that can vary. It is not based on the newer variable valve timing (VVT) engines that moved the front face forward to create room for the cam phaser.
Why would I mention this Gen II problem? Chrysler built about 10,000 Gen II Hemi engines and may have had another 1,000 in parts. The Gen III Hemi engine has 3.5 million units created so far, and that number is growing every day. This means that basic Gen III Hemi cores will be available to rebuild for a very long time! As a bonus, these are the numbers for production vehicles; there should be about 350 times as many racing engines to be rebuilt. Get ready to be busy!
Racing came easy to the Gen I and Gen II engines because they evolved with the various sports and racing venues. Chrysler race teams used the Gen II 426 Hemi for competition before it went into production. The Gen III Hemi started out more slowly relative to actual/official racing participation, but the production engines in many different vehicles are at a very high performance level.
With any engine family, there are engine builders, head specialists, and parts retailers/wholesalers that specialize in the new hardware, such as Modern Muscle Xtreme (MMX). MMX had a Gen III Hemi parts and vehicle display at the 2017 Performance Racing Industry (PRI) trade show.
The Gen III Hemi development started slowly in 2003. The 5.7L Hemi engines delivered a modest 345 hp and received many awards in the first few years. A key reason for the slow development was that the company was downsizing leading up to the Chrysler bankruptcy in 2008. Chrysler and the Gen III started to gain some momentum in 2009–2010 with the SRT models and with the Challenger Drag Pak cars.
In 2009, the Eagle 5.7L was released with an engine rated at 385–390 hp, which is a pretty good gain for an existing production engine! It is an easy engine to build and is durable, lightweight, relatively small, and responds easily to performance changes.
Chrysler’s production engineers took another, even bigger leap forward from a performance standpoint in 2011. By earlier standards, the 6.4L 392 could be considered close to a race engine with its high compression ratio (10.7:1), high valve lift (.570 inch), big valves (2.14 inch), and high-flow ports (around 330–340 cfm intake stock and more than 400 cfm ported). The 485 hp in full production/emission trim and the 1.23 hp/ci would seem to support this somewhat wild comparison. For whatever reason, all of this 392 magic and high-tech features slid in under the radar, but this high-performance package is basically ready to go racing!
Hot Rodding
The term hot rodding covers a lot of ground and could be a street rod, street machine, custom build, or one of several other options. Hot rodding began in earnest in the 1950s and 1960s and tended to focus on engine swapping, such as installing a V-8 in place of a production 4- or 6-cylinder engine, installing a big-block V-8 in place of a small-block V-8, or better yet, installing a Hemi in place of any engine! In the 1970s, 1980s, and 1990s, hot rodding seemed to go in other directions. These markets wanted a unique vehicle, and engine swapping was an easy way to obtain this goal. The Gen III Hemi engine appears to fit this market perhaps better than any earlier engine because of its unique combination of smaller size, Hemi heads, lighter weight, and huge horsepower availability.
There are many types of hot rods. One of the more popular combinations is the Gen III Hemis in early B- and E-body Chrysler products. There are motor mounts, headers, and oil pans made for this swap than any others. Shown is the 392/426 Gen III Hemi in a 1968 Charger (B-body) chassis.
In the late 1990s and early 2000s, the hot rod market began moving in the high-tech direction with fuel injection or MPI being popular. In the last 7 to 10 years, these performance customers are moving away from using the MPI system and are now trying Holley or Edelbrock carbs or one of the many new throttle body–style fuel-injection systems now available. In any case, with MPI or with a carburetor/distributor, the basic engine will probably need to be rebuilt.
If you are going to build a custom car or hot rod, you will need an engine assembly to rebuild and install in your special project. There are millions of Gen III Hemi truck engines, and they may look somewhat unique, such as this vertical throttle body mount and can easily be converted. (Photo Courtesy FCA US LLC)
Rebuild
The key word in this book is rebuild, because that is what we want to do! Rebuild is generally a verb and means