Today, the aftermarket offers handheld units that work with the production ECM and can control almost every engine function for all applications.
All Gen III Hemi production engines use multi-point injection (MPI). The MPI system uses one injection in the intake manifold port runner at the manifold face (just above the valve cover). The injectors are fed fuel from the fuel rail, which is the long tube parallel to the cam centerline that sits above the four injectors. The throttle body mounts on top of the manifold or at the front, depending upon application.
All Gen III Hemi production engines come with MPI. However, a carburetor and distributor are desired for some applications, such as hot rods, street machines, and custom builds. Prefix makes a new front cover kit for these engines that allows the use of a distributor (blue cap in upper left) and a mechanical fuel pump (used with a carburetor) mounted at the lower middle.
Horsepower Production
In the mid-1950s, the Gen I Hemi engine made almost 1 horsepower per cubic inch (hp/ci), and in 1958 its big brother the 392 was only a few horsepower short of the magic 1 hp/ci goal. The Gen II 426 Hemi was only 1 hp short of that 1 hp/ci goal in its production period through 1971. For comparison, the original Gen III 5.7L Hemi has 345 ci and was rated at 345 hp in 2003. While this isn’t a fair comparison, it illustrates that the new Gen III Hemi fits in well with the family tradition.
In the 1960s, there were only three companies that rated engines: General Motors, Ford, and Chrysler. Production engines were rated on a cold bare gross system (basically open exhaust and no accessories) and a net system, and the advertised ratings were somewhere in between. Before 1972, guidelines were just that, so any rating came with many unknowns. In an effort to improve this situation for consumers, the federal government asked the Society of Automobile Engineers (SAE) to define this engine rating system based on the new emissions regulations in 1972. The advertised rating moved closer to the net rating and the gross or cold bare gross rating went away. The switch in systems caused a big drop in the horsepower ratings for almost all engines. However, the compression ratio drop hurt the high-performance engines more because they dropped from 10.5 to 8.5 while other regular-performance engines went from 8.5 to 8.0.
Since then, government regulations have adjusted the ratings definition to more closely match the vehicle. With the new system, there is no flexibility. Government officials have been trying to get to an as-installed number, as most agree that using net ratings is misleading. Today, the system is still watched closely. There haven’t been any major revisions during the 14 years of Gen III Hemi production. This means that the rating given for your engine will be close to what you will get from the assembly when you rebuild it.
Production engines are rated in the 345-hp to 485/490-hp range with the supercharged 707-hp and 840-hp versions covering the big end. Each engine has a cover that spells out the engine or identifies it as supercharged. The covers sit on two round plugs on top of the valve covers. There are large single covers, “supercharged” and “392 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.
