The 6.4 HEMI Ultimate Engine Handbook. Many enthusiasts consider the Chrysler/Dodge 6.4 HEMI V8 engine to be one of the best in the SRT lineup today. It produces nearly 500 horsepower and lb-ft of torque from the factory, depending on the model, and has exceptional towing capacity. Chrysler began offering it as a crate engine in 2007, and it was introduced to the production market in 2012. The 6.4, also known as the 392 or Apache HEMI, is one of Dodge’s largest displacement gasoline engines currently available.
Today, we’ll take an in-depth look at the 6.4 HEMI engine and discover what makes it so unique. It has long been regarded as extremely reliable while capable of producing monstrous power, and now we’ll explain why. Everything you need to know about the Chrysler/Dodge 6.4 HEMI engine is covered in this article. We’ll start with the history of HEMI, go over the 6.4 HEMI specs and applications, and then we’ll tackle the common problems and top mod upgrades for increased horsepower and torque. Let’s get this party started.
History of the Dodge 6.4 HEMI
As previously stated, the development of Chrysler’s HEMI engine is linked to the Second World War. During the war, Chrysler built two HEMI-style engines for the US Army. The first was the AV-1790-5B, a V12 HEMI, and the second was the XIV-2220, an inverted V16 HEMI. The V12 AV was used in the M47 Patton Tank and the V16 XIV was used in the P-47 Thunderbolt aircraft. The XIV, in particular, had over 2,500 horsepower and could reach speeds of over 500 miles per hour.
From 1951 to 1959, Chrysler developed the first generation of HEMIs for automobiles after the war. These came in inline-six and V8 configurations, with displacement ranging from 240-392 cid. The second generation of Chrysler HEMI, known as the iconic 426 HEMI, lasted from 1964 to 1971. This HEMI engine was used in some of the nastiest NASCAR and muscle cars of the 1960s, making it one of the most sought-after collector’s engines today. In Top Fuel racing, some versions of the 426 HEMI have been modified to produce more than 10,000 horsepower.
HEMI’s Third Generation
This brings us to the current generation of Chrysler HEMI engines. The Gen III HEMI began in 2003 with the introduction of the 5.7 HEMI in Ram trucks. The 5.7 eventually made its way into performance sedans and muscle cars like the Charger/Challenger and 300C. Chrysler introduced a bored version with 6.1 liters of displacement in 2005, which was used for the high performance SRT-8 line, which included the 300C, Magnum, and Charger/Challenger models.
The 6.4 HEMI
Chrysler engineers released a crate version of the 6.4 HEMI engine for racing enthusiasts in 2007. Though marketed as a 6.4 L, it had the same displacement as the Gen I 392 HEMI, which ran from 1957 to 1958, and was created to commemorate the 50th anniversary of the Gen I engine.
The 6.4 HEMI was introduced to the market for the 2012 model year by Chrysler and Dodge. It was used in the Chrysler 300C, and Dodge used it in the Charger and Challenger SRT-8s. Jeep also used a 392 HEMI engine in the Grand Cherokee SRT-8. The engine eventually made its way into the Dodge Durango, Jeep Wrangler Rubicon, and Wagoneer.
Dodge also installed a version of the 6.4 in the Ram 2500/3500 and Ram Chassis Cab 3500/4500/5500 trucks beginning in 2014, and it is still available today. The engine is also still available inside the Rubicon and Durango, and also in the Charger and Challenger as part of the 392 HEMI or Scat Pack options. In addition, Chrysler is making the 6.4 HEMI engine available as a limited option for the 300C’s final year in 2023, where it was previously available from 2012 to 2014.
Although there have been rumors that Dodge is discontinuing the HEMI V8, they are still available for the 2023 model year.
Dodge 6.4 HEMI Engine Details
Applications for Chrysler 392 HEMI Vehicles
The Chrysler 6.4 HEMI engine has been used in the following vehicles:
- 2012-2014 Chrysler 300C SRT-8; 2023 Chrysler 300C SRT-8
- Dodge Challenger SRT-8; SRT 392; R/T Scat Pack (2012-Present)
- 2012-Present Dodge Charger SRT-8; SRT 392; R/T Scat Pack
- SRT-8 Jeep Grand Cherokee 2012-2021; SRT
- Dodge Ram 2500/3500 (2014-present)
- Dodge Ram Chassis Cab 3500/4500/5500 2014-Present
- Dodge Durango SRT from 2018 to the present
- 2021–2022 Jeep Grand Cherokee
- Jeep Wrangler Rubicon 392 (from 2021 to the present)
Basics of the Chrysler 392 HEMI Engine Design
The 6.4 HEMI is a 90° V8 engine with 6.4 liter (392 cid) aluminum cylinder heads and a cast iron, deep skirted cylinder block. HEMI engines, as opposed to traditional flat-topped motors, have hemispherical combustion chambers, hence the name. HEMIs have both advantages and disadvantages, but they are best known for their ability to suck in a lot of air and produce a lot of power.
The 6.4, like other Gen III HEMIs, has cross-bolted main caps and twin-spark plug cylinders. The compression ratio sits at 10.9:1, and the engine is naturally aspirated. The redline can be reached at 6,400 RPM. The crankshaft is made of forged steel, the pistons are made of hypereutectic aluminum, and the connecting rods are made of powdered metal I-beam. Oil-cooling jets are also included in the pistons to help reduce cylinder temperatures and pressure. The bore and stroke are 103.9mm (4.09′′) and 94.6mm (3.72′′), respectively, making it a stroked version of the 6.1 liter HEMI it replaced.
Dodge employs an old-school overhead valve (OHV) pushrod design for the valvetrain. Each cylinder has two valves, for a total of sixteen valves. The intake valves are 2.14″ in length and the exhaust valves are 1.65″ in length, making them quite large. The durations of the single camshaft are 286° for intake and 288° for exhaust, with lifts of.571″ for intake and.536″ for exhaust. All 392 HEMI engines use variable camshaft timing (VCT), which increases power while decreasing fuel consumption.
Manifolds and HEMI MDS
All 6.4 HEMI engines with automatic transmissions come with a Multi-Displacement System, also known as MDS, which almost everyone despises. MDS is essentially cylinder deactivation technology that increases fuel economy while decreasing emissions output. We previously examined this in depth in our 5.7 and 6.4 HEMI MDS Guide, so be sure to read that for more information.
The intake manifold on the 6.4 HEMI engine is a little different. It employs a “active runner” system, which means that the ECU can adjust the runner size to optimize horsepower and torque at various RPM and throttle settings. The throttle body is 80mm in diameter, and the entire manifold is made of composite plastic rather than aluminum. The tubular exhaust manifold performs admirably for a stock unit.
Chrysler/Dodge initially rated the Apache HEMI for 470 horsepower and 470 lb-ft of torque, depending on the model. In 2015, the Challenger and Charger gained 485 horsepower and 475 pound-feet of torque.
The 6.4 HEMI Truck Version
In addition to the 392 HEMI found in Chrysler, Dodge, and Jeep Sedans and SUVs, there is a Ram Truck version. The engines are similar, but they’re designed and tuned for low-end torque and towing rather than high-rpm performance and racing. The truck version debuted in 2014, with a reinforced block known as a “Big Gas Engine” BGE block. This block proved superior and was eventually used in all 6.4 HEMI applications, even the non-truck versions.
Distinctions between trucks and non-trucks Apache HEMIs feature an intake manifold with a top-feed throttle body (rather than a side-feed throttle body) and a lower compression ratio of 10.0:1. All of the pistons, rods, and valves are the same size, but the camshafts are less aggressive. Furthermore, the exhaust manifold on the truck versions is made of cast iron and is more restrictive.
Power output is also significantly lower in truck versions. Power ranges from 366-410 horsepower and sits at 429 lb-ft of torque for all. However, as previously stated, the truck versions were designed for towing and high load capacity. The 6.4 HEMI engine in Ram trucks has a towing capacity of more than 20,000 pounds, making it suitable for almost any application.
Dodge 6.4 HEMI Reliability and Common Issues
Overall, we believe the Chrysler/Dodge 6.4 HEMI engine is a dependable motor. While it has only been in production since the 2012 model year, it has performed admirably since then. Given the incredible amount of power and towing capacity the 392 HEMI is capable of, the fact that many have surpassed 100,000 miles is quite remarkable.
However, the 6.4 HEMI has a few underlying issues that some owners have discovered. It’s not enough to say the engine is unreliable or prone to problems; it’s also necessary to mention them. The MDS, engine ticking, transmission failure, and misfiring are the most common 392 HEMI problems.
We previously published a guide to the four most common 6.4 HEMI engine issues. We’ll just summarize the issues here, so make sure to read the guide for a more in-depth breakdown.
The Most Common Dodge 6.4 V8 Issues
The following are the most common 6.4 HEMI engine issues:
- The MDS system from Chrysler
- The engine is ticking.
- Transmission breakdown
The first topic will be the issues with Chrysler’s Multi-displacement system (MDS), also known as cylinder deactivation. MDS solenoid failures have been reported by some owners with high mileage (100,000+ miles). Although it is not a widespread problem, a few people have complained.
Engine ticking is a somewhat contentious topic, with some claiming that it is normal and not a problem at all. Others, on the other hand, blame faulty lifters and seized rollers. These are also issues with the 5.7 liter HEMI, indicating that the problem is not limited to the 6.4 valvetrain.
Then there’s transmission failure, which is a tricky problem because it’s not caused by the engine. It is mostly limited to the Ram 2500/3500 series, but some people have reported premature failure. It’s only a few reported failures, so it’s not a widespread problem.
The final point to mention is spark plug misfires. This is yet another problem with the 5.7 HEMI. Both engines have twin-spark plugs and have been known to go through plugs quickly. Maintaining your HEMI on a regular basis is the best way to avoid spark issues.
Performance and Upgrades for the Chrysler 6.4 HEMI
Let us now discuss the most important aspect of the 6.4 HEMI engine, its performance. Within the SRT line, output peaks at 485 horsepower and 475 lb-ft of torque, making it a formidable track and drag strip performer. The 6.4 HEMI in the Ram Chassis Cab 5500, on the other hand, is rated to tow more than 21,000 lbs, indicating that it’s also quite capable of doing some serious work.
While those are all respectable stock numbers, with the right modifications, the 6.4 HEMI can easily outperform both of them. We’ll go over some of the best mods for the 6.4 HEMI to increase horsepower and torque.
392 HEMI Upgrade Manuals
The following are the top five best 6.4 HEMI upgrades:
- The throttle body
Tuning, an upgraded intake, a larger throttle body, upgraded headers, and an upgraded camshaft are the top five best 6.4 HEMI mods. By far the best bang for your buck will be tuning, which will add 5-15% power without requiring any hardware changes. It’s a great mod for those who want to boost their performance without having to deal with complicated installations.
Following that, an upgraded cold air intake for the 6.4 HEMI is a fantastic mod. It will increase airflow into the engine and can add 5-15 horsepower with tuning. A larger throttle body after an intake will allow for even more airflow into the engine, which is especially important for those with forced induction.
Upgraded 6.4 HEMI long tube headers are also one of the top mods available. They increase wheel horsepower by up to 35 percent while really opening up the HEMI to make it scream. Another good mod is more aggressive camshafts for the 6.4 HEMI. They can add more than 100 horsepower and allow you to build the engine exactly how you want it: with a focus on top end power or a beefy midrange.
Upgrading the 392 HEMI intake manifold will also result in unexpected gains. Upgrading the intake manifold on a boosted Apache HEMI is a great addition to a larger throttle body. The two together can add as much as 20 wheel horsepower, and really smoothen out the power band.
Finally, if you want to make more than 600 horsepower as cheaply as possible, you should consider a 392 HEMI supercharger. Supercharging can easily add 100+ horsepower while keeping the engine mostly stock.
Summary of the Dodge 6.4 HEMI Engine
Overall, we are huge fans of the 6.4 HEMI, as the engine has proven to be a dependable but performance-oriented beast. It has nearly 500 horsepower and lb-ft of torque out of the box, but that only scratches the surface of what it’s capable of. Because it has a larger displacement engine than the Demon or Hellcat motors, its ultimate potential is unknown.
Yet, even with all of that performance and potential, the 6.4 HEMI has shown itself more than capable of respectably powering the Medium Duty and Heavy Duty version of the Ram Truck series. This versatile engine has a towing capacity of over 21,000 pounds and is a true workhorse.