6.4 HEMI Engine
| | |

6.4 HEMI Ultimate Engine Guide

Chandler Stark

Meet Chandler

Chandler is an automotive expert with over a decade of experience working on and modifying cars. A couple of his favorites were his heavily modded 2016 Subaru WRX and his current 2020 VW Golf GTI. He’s also a big fan of American Muscle and automotive history. Chandler’s passion and knowledge of the automotive industry help him deliver high-quality, insightful content to TuningPro readers.

For many enthusiasts, the Chrysler/Dodge 6.4 HEMI V8 engine is one of the top engines in the SRT lineup today. Depending on the model, it produces nearly 500 horsepower and lb-ft of torque from the factory, and boasts outstanding towing capacity in Ram trucks. Starting in 2007, Chrysler made it available as a crate engine, and in 2012 they introduced it to the production market. Alternatively known as the 392 or Apache HEMI, the 6.4 is one of the largest displacement gasoline engines available from Dodge’s lineup.

Today, we’re going to take an in-depth look at the 6.4 HEMI engine and find out what makes it such a special motor. It has long been regarded as extremely reliable while being capable of making monstrous power, and now we’re going to break down why. This article will cover everything you need to know about the Chrysler/Dodge 6.4 HEMI engine. 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 started.

*Previously, we looked at the Dodge 6.4 HEMI vs 5.7 HEMI, so make sure to give that a read, too. 

6.4 HEMI Engine
Credit: Ammar Shaker/Wikipedia

Dodge 6.4 HEMI History

As we’ve mentioned before, the creation of Chrysler’s HEMI engine is actually related to the Second World War. During the war, Chrysler produced two different HEMI-style engines for the U.S. Army. First was the AV-1790-5B, which was a V12 HEMI, and second was the XIV-2220, which was an inverted V16 HEMI. The Army used the V12 AV in the M47 Patton Tank and the V16 XIV inside the P-47 Thunderbolt aircraft. The XIV in particular made more than 2,500 horsepower and could reach speeds of over 500 mph.

Following the war, Chrysler developed the first generation of HEMIs for automobiles from 1951-1959. These included both inline-six and V8 configurations, and ranged from 240–392 cid in displacement. The second generation of Chrysler HEMI lasted from 1964-1971, you probably know it as the iconic 426 HEMI. This HEMI powered some of the nastiest NASCAR and muscle cars of the 1960s, making them some of the most sought out collector’s engines today. Some versions of the 426 HEMI have been modified to make more than 10,000 horsepower in Top Fuel racing applications.

The Third Generation of HEMI

That brings us to the third and current generation of the Chrysler HEMI engine. The Gen III HEMI began in 2003 with the release of the 5.7 HEMI inside the Ram trucks. Eventually, the 5.7 also found its way into performance sedans and muscle cars like the Charger/Challenger and 300C. In 2005, Chrysler released a bored version with 6.1 l of displacement, which was used for the high performance SRT-8 line, including the 300C, Magnum, and Charger/Challenger models.

The 6.4 HEMI

In 2007, the Chrysler engineers released a crate version of the 6.4 HEMI engine for racing enthusiasts. Though marketed as a 6.4 L, it had the same displacement as the Gen I 392 HEMI that lasted from 1957–1958, and was made in honor of the Gen I engine’s 50th anniversary.

For the 2012 model year, Chrysler and Dodge brought the 6.4 HEMI to the production market. Chrysler used it in the 300C, and Dodge put it inside the Charger and Challenger SRT-8s. Jeep also used a version of the 392 HEMI inside the Grand Cherokee SRT-8. Eventually, the engine also found its way into the Dodge Durango and Jeep Wrangler Rubicon and Wagoneer.

Starting in 2014, Dodge also put a version of the 6.4 inside the Ram 2500/3500 and Ram Chassis Cab 3500/4500/5500 trucks, where it is still currently 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. Also, for the final year of the 300C in 2023, Chrysler is making the 6.4 HEMI engine available as a limited option, where it was previously available from 2012-2014.

There have been rumors that Dodge is canceling the HEMI V8, but as of now they are still available for the 2023 model year.

Dodge 6.4 HEMI Engine Specifications

Engine Name6.4 HEMI
Engine FamilyGen III HEMI
Production Years2007-Present
Displacement6.4 Liters (392 cid)
AspirationNaturally Aspirated
Configuration90° V8
Compression Ratio10.0:1 (Truck); 10.9:1 (SRT)
Bore and Stroke103.9mm (4.09″) x 94.6mm (3.72″)
Valve TrainOHV, 16 Valve, VCT
Fuel SystemElectronic Fuel Injection
Head MaterialAluminum
Block MaterialCast Iron
Horsepower Output360-485 horsepower
Torque Output430-475 lb-ft of torque

Vehicle Applications

The Chrysler 6.4 HEMI has appeared in the following vehicles:

  • 2012–2014; 2023 Chrysler 300C SRT-8
  • 2012–Present Dodge Challenger SRT-8; SRT 392; R/T Scat Pack
  • 2012–Present Dodge Charger SRT-8; SRT 392; R/T Scat Pack
  • 2012–2021 Jeep Grand Cherokee SRT-8; SRT
  • 2014–Present Dodge Ram 2500/3500
  • 2014–Present Dodge Ram Chassis Cab 3500/4500/5500
  • 2018–Present Dodge Durango SRT
  • 2021–2022 Jeep Grand Wagoneer
  • 2021–Present Jeep Wrangler Rubicon 392

Engine Design Basics

The 6.4 HEMI is a 6.4 liter (392 cid) 90° V8 engine with aluminum cylinder heads and a cast iron, deep skirted cylinder block. Compared with traditional flat-topped motors, HEMI engines have hemispherical shaped combustion chambers, hence the name. HEMIs have both advantages and disadvantages, but for the most part they are known for being able to suck in lots of air and produce violent amounts of power.

Like other Gen III HEMIs, the 6.4 has cross-bolted main caps and the cylinders have a twin-spark plug design. The compression ratio sits at 10.9:1, and the engine is naturally aspirated. The redline reaches all the way to 6,400 RPM. Internally, the crankshaft is forged steel, the pistons are hypereutectic aluminum, and the connecting rods are powdered metal I-beam. The pistons also have oil-cooling jets to reduce cylinder temperatures and pressure. The bore and stroke are 103.9mm (4.09″) x 94.6mm (3.72″), making it essentially a stroked version of the 6.1 liter HEMI it replaced.

For the valvetrain, Dodge uses an old school overhead valve (OHV) pushrod design. There are 2 valves per cylinder, for 16 valves total. The intake valves are 2.14” and the exhaust valves are 1.65”, making them pretty large. The single camshaft has durations of 286° for intake and 288° for exhaust, with commensurate lifts of .571” for intake and .536” for exhaust. All 392 HEMI engines use variable camshaft timing (VCT), which adds power and improves fuel economy.

HEMI MDS and Manifolds

For all 6.4 HEMI engines with automatic transmissions, equipped is a Multi-Displacement System, also known as MDS, which pretty much everyone has hated. Essentially, MDS is cylinder deactivation technology to increase fuel economy and reduce emissions output. Previously, we looked in-depth with our 5.7 and 6.4 HEMI MDS Guide, so make sure to check that out for more information.

The intake manifold on the 6.4 HEMI engine is somewhat unique. It uses an “active runner” system, which means the ECU can vary the runner size to optimize horsepower and torque at each RPM and throttle range. The throttle body is 80mm, and the entire manifold is made from composite plastic instead of aluminum. The tubular exhaust manifold flows exceptionally well for a stock unit.

Depending on the model, Chrysler/Dodge first rated the Apache HEMI for 470 horsepower and 470 lb-ft of torque. In 2015, power improved to 485 horsepower and 475 lb-ft of torque inside the Challenger and Charger.

The Truck version of the 6.4 HEMI

In addition to the 392 HEMI found in the Chrysler, Dodge, and Jeep Sedans and SUVs, there is also a version specifically for Ram Trucks. The engines are similar, but they are built and tuned more for low-end torque and towing than for high rpm performance and racing. When the truck version was introduced in 2014, it featured 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.

Differences between the truck and non-truck Apache HEMIs include the intake manifold, which on trucks has a top-feed throttle body (instead of side-feed), and a lower compression ratio at 10.0:1. The pistons, rods, and valve sizes are all the same, but the camshafts are less aggressive. In addition, the exhaust manifold is cast iron on the truck versions, and is more restrictive.

Power output is also much lower on the truck versions. Power ranges from 366-410 horsepower and sits at 429 lb-ft of torque for all. However, as we mentioned, the truck versions were built more for towing and high load capacity. Inside the Ram trucks, the 6.4 HEMI has a towing capacity of more than 20,000 lbs, making it suitable for pretty much anything.

Dodge 6.4 HEMI Common Problems and Reliability

Overall, we consider the Chrysler/Dodge 6.4 HEMI engine to be a relatively reliable motor. While it has only been around in production form since the 2012 model year, it has performed exceptionally well since then. Especially considering the incredible amount of power and towing capacity the 392 HEMI is capable of, the fact that many have made it well past 100,000 miles is pretty remarkable.

However, the 6.4 HEMI does have a few underlying issues that have crept up for some owners. It’s not enough to call the engine unreliable or prone to problems, but it’s still important to mention them. The most common 392 HEMI problems are with the MDS, engine ticking, transmission failure, and misfiring.

Previously, we wrote a guide to the 4 most common 6.4 HEMI engine problems. We’re just going to summarize the issues here, so make sure to check out the guide for the full in-depth breakdown.

Most Common Problems

The most common 6.4 HEMI engine problems are:

  • The Chrysler MDS system
  • Engine ticking
  • Transmission failure
  • Misfiring

The first thing we’ll go over are the problems with Chrysler’s Multi-displacement system (MDS), more commonly known as cylinder deactivation. Some owners with high mileage (100,000+ miles) have reported problems with MDS solenoid failures. It’s not a widespread issue, but a few people have complained.

Engine ticking is a somewhat controversial issue, because some people will claim that the ticking is normal and not a problem at all. Others, however, point to faulty lifters and seized rollers as the issue. These are also problems on the 5.7 l HEMI, so it’s not just isolated to the 6.4 valvetrain.

Next is transmission failure, and this is another tricky issue, as it’s not with the engine itself. It’s mainly limited to the Ram 2500/3500 series, but some people have experienced issues with premature failure. It’s only a few reported failures, so again it’s certainly not a widespread issue.

The last thing we’ll bring up are spark plug misfires. This is another issue that also crept up on the 5.7 HEMI. Both engines use a twin-spark plug design, and they have been known to go through plugs fairly quickly. Making sure you keep up on timely maintenance is the best way to avoid spark issues on any HEMI.

Chrysler 6.4 HEMI Performance and Upgrades

Now let’s talk about the most important part of the 6.4 HEMI engine, the performance. Inside the SRT line, output peaks at 485 horsepower and 475 lb-ft of torque, making it quite formidable at the track and on the drag strip. On the other hand, inside the Ram Chassis Cab 5500, the 6.4 HEMI is rated to tow more than 21,000 lbs, showing it’s also quite capable of doing some serious work.

And while those are all pretty good numbers stock, with proper modifications the 6.4 HEMI can easily beat both of those numbers without breaking a sweat. Below, we’ll go over some of the top mods for the 6.4 HEMI to bring about the most horsepower and torque.

392 HEMI Upgrade Guides

The top 5 best 6.4 HEMI upgrades are:

  • Tune
  • Intake
  • Throttle body
  • Headers
  • Camshafts

The top 5 best 6.4 HEMI mods are tuning, upgraded intake, bigger throttle body, upgraded headers, and an upgraded camshaft. By far, the best bang for your buck is going to be tuning, which will add 5-15% power without any hardware modifications. It is a great mod for those looking to get some extra performance without any complicated installations.

Next up, an upgraded cold air intake for the 6.4 HEMI is a great mod. It will allow for increased airflow into the engine, and with tuning can add 5-15 horsepower. After an intake, a larger throttle body will allow for even more airflow into the engine, and it’s especially important for those with forced induction.

Upgraded 6.4 HEMI long tube headers are also one of the top mods available. They add as much as 35 wheel horsepower, while really opening up the HEMI to make it scream. More aggressive camshafts for the 6.4 HEMI are another solid mod. They can add more than 100 horsepower, and really allow you to build the engine how you want: prioritizing top end power or a beefy midrange.

Upgrading the 392 HEMI intake manifold will also net surprising gains. If you have a boosted Apache HEMI, upgrading the intake manifold 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 cost effectively as possible, you’ll probably want to look at a 392 HEMI supercharger. Supercharging will easily add 100+ horsepower while keeping a mostly stock engine.

Dodge 6.4 HEMI Engine Summary

Overall, we are really big fans of the 6.4 HEMI, as the engine has more than proven itself to be a reliable but performance oriented beast. It makes nearly 500 horsepower and lb-ft of torque from the factory, but that’s just scratching the surface of what it’s really capable of. It’s actually a larger displacement engine than the Demon or Hellcat motors, so you can only guess as to what its ultimate potential is.

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 can tow more than 21,000 lbs stock, and is an absolute workhorse.

Do you own a 6.4/392/Apache HEMI engine inside a MOPAR vehicle? Have you decided to build out yours with some internal mods or forced induction? Let us know in the comments below!

Similar Posts

2 Comments

  1. I bought a Ram Power Wagon (2022) with the 6.4L. It is a beast! It is fast and has gotten to 23,000 miles. Its only defective is gas mileage.I get 8-9 mpg in town and 13 in the highway. I expected it to love gas, so not a major problem for me. I have a 7 year extended warranty, so no mods until then!
    Looking forward to an overland trailer next year!

  2. Great content. Was reading with pleasure. Myself new in HEMI world. Own 2012 Jeep GC SRT8.
    Amazing car.
    Have feeling that MDS has some delays in on/off. What could be reason?
    Thanks.

Leave a Reply

Your email address will not be published. Required fields are marked *