Dodge HEMI 6.4L: Everything You Need To Know

HEMI engines can be traced way back to the 1950s when Chrysler’s revolutionary hemispheric combustion chambers took over the automotive arena by having a more efficient and powerful engine.

In retrospect, the 392 HEMI can be found across Chrysler products in late 1950 before its re-emergence until 2011, carrying the same confidence they had over the years.

But apart from the respect of its competitive peers, what does the 392 HEMI have? Let’s have a brief tour of the 6.4 L HEMI engine.

What are Dodge HEMI 6.4 L Engines?

Chrysler created a wide range of HEMI engines, and they launched a more powerful and larger 392 cubic-inch HEMI in 2005 with a factory-rated output of 525 HP and 510 lb-ft of torque. The engine has been available in the market since 2007 as a crate engine under the badge 392 HEMI.

There are several improvements, including stronger forged aluminum-alloy pistons; it is also more powerful and produces more torque deemed suitable for towing and hauling like its alternate turbocharged diesel version – the 6.7 L ISB Cummins.

But the production version came out in the form of the 2011 Dodge Challenger SRT 8 equipped with variable camshaft timing and MDS in vehicles with automatic transmissions. The newly launched 392 HEMI is based on the third-generation 5.7 L HEMI, codenamed as “The Eagle,” while the 6.4 is codenamed as “Apache,”; sharing few parts with the 392 HEMI crate engine.

In addition to that, Special-Edition Chargers as well as Challengers installed with this engine, and the machines themselves, will have the 392 HEMI badge in commemoration of the first-generation engine of the same displacement.

An updated 2015 version of the 392 HEMI was released with a 485 horsepower output and 475 lb-ft of torque in the Challenger SRT 392, Charger, and R/T Scat Pack Models.

Engine Specifications and Design:

  • Production Run: 2011 – Present
  • Cylinder Head Material: Aluminum
  • Cylinder Block Material: Cast-iron
  • Configuration: V8
  • Bore: 103.9 mm
  • Stroke: 94.6 mm
  • Valvetrain: OHV, two valves per cylinder
  • Displacement: 6.4 L (6407 cc)
  • Compression Ratio: 10.9 for 6.4 L HEMI SRT and 10.0 for 6.4 HEMI RAM Trucks
  • Weight: 500 lbs.
  • Maximum HP: 485 HP at 6,000 RPM
  • Maximum Torque: 475 lb-ft at 4,800 RPM

The framework of the 6.4 L HEMI can also be found in the 6.1 and 5.7 L HEMI; they are the same but have different bores and strokes. The engine design revolved around the 90-degree cylinder bank orientation.

The 6.4L HEMI engine is an over-square engine with a 103.9 mm cylinder bore, 94.6 mm piston stroke, and 10.9 compression rating for most SRT vehicles. Oversquare engines mean that the cylinders have a greater bore than the stroke, making the bore/stroke ratio greater than 1. Resulting in higher RPM range – and more power, without overplaying the piston speed.

The cylinder block comprises deep-skirt cast-iron material with cross-bolted main bearing caps and aluminum alloy headers.

While the aluminum heads and deep-skirt cast-iron block are used on the 3.6L Pentastar V6, the cross-bolted main bearing caps are designed for special performance modifications. These cross-bolted caps are cast into the ending block to increase the block’s rigidity, so everything stays intact to handle large amounts of energy, especially when maximizing engine power.

The 6.4 HEMI engine also features piston cooling jets or squirters. These squirters spray engine oil underneath each piston to regulate combustion heat for better performance. And for this reason that Chrysler integrated an oil-to-water oil cooler to provide additional cooling under extreme conditions. This cooler not only makes the engine safe but also stretches the engine’s lifespan and longevity.

Furthermore, the 6.4 HEMI has better connecting rods made of higher-strength powder material and larger diameter flat-top pistons with fully floating pins.

The 6.4 HEMI cylinder heads are also identical to those of 5.7 HEMIs, which have two valves and two spark plugs in each cylinder, in addition to the oval-shaped, semi-hemispherical combustion chambers. These heads feature a larger cross-sectional head port area that provides a better airflow on both the intake and exhaust ports – 11% intake and 13% exhaust.

The headcovers are made from plastic and a plastic intake manifold with shorter runners for high-speed SRT vehicles such as Challenger and Charger. At the same time, the truck 6.4L HEMI has an active dual-runner-length intake manifold for low to mid-range engine speeds without compromising the higher-end power of SRT V8s.

Both the high-speed and truck version shares the drive-by-wire throttle bodies. The 6.4 truck engine has a variable valve timing, cam-in-block, that uses a hydraulic cam phasing system developed by Chrysler. Valve-train consists of hydraulic roller lifters and sodium-filled exhaust valves.

The truck engine is more efficient by integrating a cylinder deactivation system called Multi Displacement System or MDS. This mechanism turns off fuel in four cylinders when power is not demanded. It cuts out the valve lifters of the involved cylinders in order to eliminate pumping losses.

The power rating of 6.4 HEMI varies on different applications that range from 470 – 525 HP with 470 – 510 lb-ft of torque available.

Applications of Dodge HEMI 6.4L:

  • Dodge Challenger SRT 392
  • Dodge Durango SRT
  • Dodge Charger SRT 392
  • Jeep Grand Cherokee SRT
  • Jeep Wrangler Unlimited Rubicon 392
  • Jeep Grand Wagoneer

HD Truck and Cab Chassis:

  • 2500 and 3500 Pickup, 3500 SRW: 410 HP and 429 lb-ft
  • 3500 Mega Cab, 3500 DRW Cab Chassis, 3500 SRW/DRW with Aisin Transmission: 370 HP and 429 lb-ft
  • 4500 and 5500 Cab Chassis: 366 HP and 429 lb-ft

Engine Tuning, Upgrades, and Modifications

The 6.4 L HEMI engines, by design, are not ready for a more significant power production since their internals are not capable of handling such a demanding workload. Yes, it is powerful, it is used for towing and hauling, but it does not equate to aggressive power production.

But you can opt to tune your engine and reach 410 HP from its stock form. To add, by reflashing the ECU, you will also open up the engine potential, of course, with the performance parts of your choice.

Problems Surrounding Dodge HEMI 6.4L Engine:

You can go no wrong with the high-performance engine in 392 HEMI. It is well-designed, efficient, and carrying the non-existent engine design flaw. But even with the reputation, it displayed throughout generations, the HEMI engines – especially the 392, are no exception to some issues that might arise during its lifetime. Here are some typical troubles:

The first is a faulty Multi-Displacement System. 

This technology is top-notch, providing a far more efficient engine by shutting down the cylinder when necessary, especially on conditions that require no enormous amounts of power. It is also integral in pumping out more power while being effective during lower power situations.

However, the MDS sometimes fail, particularly the solenoids; some takeaways include a clunky MDS, too. But the long-term effects of such is still under investigation and are mere speculations since Chrysler did not announce this.

Note that prolonged cylinder shut can have adverse effects on the spark plugs, oil, and lubrication. Since running too cold may wear down the cylinder over time as well as premature spark plug fouling.

Next is the Engine Tick.

This issue is also common to the 5.7 L HEMI and has different manifestations on a wide range of applications. Some say that the ticking is regular and does not affect any components, reliability, and performance. But, contrary to that statement, this ticking pushed some owners to replace the engine completely.

The engine tick can be due to lifter roller problems partially attributed to the multi-displacement system. Lifter problems result in restrictive airflow that causes the lifters to contact the cam lobes and produce an engine ticking sound.

It can cause further headaches since metal-to-metal contact leaves a metal shaving that mixes with engine oil. If that happens, further engine damage would likely occur.

The third one is Transmission Failure. 

Some 392 HEMI engines are paired to a different transmission that depends on the vehicle. Trucks such as the RAM 2500 and 3500 are way too demanding due to their heavy towing loads that put a lot of transmission stress. This results in premature wear and tear, and if abused, engine failure. This issue can occur in Chrysler, Dodge, and Jeep models.

Though it is a small percentage, it should be addressed.

And the last one is the Misfiring problem.

Misfires can also be the resulting manifestation of MDS Solenoid issues or the lifter roller. It is not a common failure, though, since spark plugs are normal wear and tear items that need replacement at a particular time, like ignition coils. Misfires, however, are symptoms of yet another underlying problem.

Spark plugs are usually replaced every 60,000 to 80,000 miles. And since the 392 HEMI uses two spark plugs per cylinder to a total of 16 spark plugs, in addition to the standard eight ignition coils, which should be replaced every 100,000 miles. Do not overlook these components, as they play a vital role in engine performance.

Summary

It remains one of the most efficient truck and high-speed performance engines. In stock form, it can provide monstrous numbers, which are not only reliable but also lasts hundreds of thousands of miles. It is also regarded as the strongest atmospheric pushrod engine to date.

The MDS technology brought this engine to a more efficient machine, creating better opportunities for other engines of the same design to come through.

However, the stock 6.4L HEMI is not built to boost and generate more power because the stock bottom end cannot accommodate that; the pistons are not forged, and there is not enough cushion between the top of the piston and ring lands. The exhaust manifold may deform due to overheat and blow the studs.

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