Exploring the Legacy: The Evolution of Chrysler’s 6.4L Hemi Engine in Trucks

Exploring the Legacy: The Evolution of Chrysler’s 6.4L Hemi “Apache” Truck Engine

With the constant war waging against the internal combustion engine by the electric car, there are increasingly less and less reasons you can argue on why these dinosaur machines should stick around. At any rate, we should enjoy them while they are here. So, over the next few weeks we will be covering the history and background of the best 6.4 V-8 Hemi truck engines on the market so you can go get one now, and have fun while you can.

This article covers the history, engineering, and reliability of the best gasoline truck engine Chrysler has produced: the 6.4L V-8 Hemi “Apache.”

Chrysler’s Hemi Engine History

To understand the 6.4L Hemi, we have to look at what came before. Up until 2002, Chrysler had offered the 8.0L Magnum V-10 engine, producing  300 hp and 450 lb-ft of torque. A monster of a gasoline engine, it rivaled the 5.9L Cummins engines available at the time In both horsepower and torque up until the end when the Cummins surpassed its torque output by a mere 10 lb-ft of torque.

When the V-10 ended production in 2002, Chrysler had no large displacement gasoline engine as an alternative to the Cummins available in any of their trucks.

Starting in 2014, Chrysler engineers debuted the new 6.4L Hemi engine, code named Apache.

What is the 6.4L “Apache” Hemi?

The 6.4L Apache displaces 392 cu-in, and as a medium-duty commercial truck option, falls in line with the 6.7L Cummins medium-duty rating, as well.

Pulling from Chrysler’s long history of engines, going all the way back to World War II, the Apache features high end durability enhancements.

Key Engineering Features:

• Deep-Skirt Cast Iron Block: Provides extreme rigidity.
• Sodium-Filled Exhaust Valves: To handle higher heat loads during towing.
• Forged Internals: Including a forged steel crankshaft and aircraft-grade stainless steel gaskets.
• High-Efficiency Oil Cooling: Piston jets and an oil cooler designed via computational fluid dynamics.

All forged internals, with a cast iron block, cross bolted main-bearing caps, and 356 aluminum—and the list keeps going and going.

6.4L Hemi Truck Engine Specs

Competing with Cummins

An active dual-runner-length intake manifold, that boosts both low and high end power by maximizing the natural supercharger effect of the manifold, and a 10.9:1 compression ratio gives this big engine 410 hp and 429 lb-ft of torque.

Variable valve timing through the use of a hydraulic cam phasing system, ensures that the engine, despite running on mid-grade 89 octane fuel for maximum output, can run seamlessly on regular gasoline.

A unique dual-spark system on the engine gives two spark plugs per cylinder, with the coil plug firing the plug it resides over and a wire that runs across the engine to the opposite bank to fire that plug.

The extra plug fires during the power stroke to more fully burn the fuel in the cylinder, which provides more power in the down stroke and also numbers the amount of catalyst plates needed In the exhaust system.

This also has the benefit of allowing the primary spark plug to fire closer to top dead center, increasing torque and cutting NOx emissions.

Let’s talk about the heart of the 6.4L Hemi’s breathing system.

Chrysler equipped this engine with a composite “active” intake manifold sporting variable-length runners – a clever setup that lets the engine adapt for both low-end torque and high-RPM power.

This innovation is no afterthought; it’s the kind of engineering you’d expect from a company chasing both muscle and efficiency.

The throttle body is no slouch, measuring in at a hefty 80mm with a sturdy four-bolt mounting pattern. It’s fully electronically controlled, ensuring crisp throttle response whether you’re pulling a trailer or just having a little fun off the line.

Fuel delivery is handled by different injectors depending on application. Car and SUV versions of the 6.4L Hemi use 27 lb/hr injectors at 58 PSI, while the medium and heavy-duty truck variants step up to 31 lb/hr injectors at the same pressure.

Both make use of modern USCAR EV6 connectors for reliability and ease of service, though neither is flex-fuel capable straight from the factory.

This collection of components ensures the 6.4L Hemi breathes deep, burns clean, and delivers the kind of punch you’d expect from a descendant of Chrysler’s legendary engine lineup.

Read More: 2UZ-FE 4.7L : Toyota’s Heavyweight V8

Multi Displacement System

Featuring a cylinder deactivation system called MDS (multi displacement system). The engine has the ability to shut off fuel in the passenger bank of the engine when power is not needed.

This equipment was part of the initial design of the Hemi engine, not an afterthought, so it fully integrates into the engine design. This improved reliability by reducing complexity and lowered the manufacturing cost.

How it works is a hydrualic lifter activates, which cuts off the valve lifters so that there is no loss of energy by pumping air through those cylinders and compressing it.

The engine can complete this transition in less than .04 seconds, and unless you have super human senses, you will never know it is there.

Currently the 6.4L Hemi is only available in RAM HD trucks. Which paired to either the six-speed 68RFE automatic transmission or the six-speed Aisin-Seiki AS69RC medium-duty truck transmission.

Reliability: Common 6.4L Hemi Problems

While built for commercial durability, the 6.4L Hemi is not without faults. Here are the most common issues owners face:

1. Camshaft and Lifter Failure

One of the primary concerns with the 6.4-liter Hemi engine is the potential for camshaft and lifter failure. This issue often leads to noticeable ticking sounds, decreased performance, and can result in expensive repairs if not addressed promptly.

2. Exhaust Manifold Bolt Breakage

Drivers often report broken exhaust manifold bolts, which can cause exhaust leaks. Over time, this issue can lead to decreased engine efficiency and increased emissions, requiring attention to prevent further complications.

3. Transmission Challenges

While not directly part of the engine, the transmission of vehicles equipped with the 6.4-liter Hemi is sometimes noted for rough shifting. This can affect overall driving experience and longevity if not serviced regularly.

4. Cooling System Concerns

Some users have highlighted cooling system inefficiencies. The engine may run hotter than expected, especially under heavy loads, necessitating vigilance and regular maintenance checks.

5. Fuel Economy

Considering its power, the 6.4-liter Hemi is not renowned for fuel efficiency. Owners seeking improved mileage may find this aspect a challenge without sacrificing performance.

Maintenance Tips

• Regular Oil Changes: Keeping up with oil changes can help mitigate wear and tear, especially concerning cam and lifter issues.
• Routine Inspections: Regular checks of the exhaust system and cooling components can prevent small problems from becoming major ones.
• Proper Load Management: Avoiding excessive towing beyond the engine’s capacity can prevent overheating and undue stress.

By addressing these concerns proactively, owners can enhance the reliability and longevity of the 6.4-liter Hemiengine.

FREQUENTLY ASKED QUESTIONS

What is the 6.4 liter “truck Hemi” V8 engine and when was it launched?

The 6.4L Hemi V8 (Apache) is a heavy-duty gasoline engine produced by Chrysler, specifically designed for RAM 2500/3500 trucks and chassis cabs. Debuting in 2014, it produces up to 410 hp and 429 lb-ft of torque, featuring a cast-iron block and sodium-filled exhaust valves for maximum durability.

This engine was specially crafted for heavy-duty applications, particularly in Ram pickups and chassis cabs. Although it shares the same displacement, the 6.4L truck Hemi is distinct from the 6.4L SRT Hemis found in non-SRT vehicles. The truck version focuses on durability and torque to handle heavy loads, setting it apart from the sportier SRT variants that deliver 470-485 hp and 470-475 lb-ft of torque.

By creating a powerplant tailored for tough tasks, Chrysler ensured that the 6.4L Apache meets the demanding needs of commercial and heavy-duty users while maintaining performance and reliability.

Read More: Unleashing Power: The 6.4L HEMI V8 Engine Explained

What are the engine specifications for the 6.4L HEMI, such as bore, stroke, and displacement?

Engine Specifications:

• Bore and Stroke: The engine features a bore of 103.9 mm (4.09 in) and a stroke of 94.6 mm (3.72 in), contributing to its 6,417 cc (392 cu in) displacement.
• Materials: The cylinder block is constructed from durable cast iron, while the cylinder head utilizes lightweight aluminum.
• Configuration: This V8 engine operates with two valves per cylinder, employing an OHV valvetrain layout for efficient performance.
• Fuel System: It runs on gasoline, with a sequential multi-port injection system ensuring optimal fuel delivery.

Performance:

• Power Output: Depending on the application, the 6.4L Hemi generates between 366-485 horsepower (273-362 kW).
• Torque: It delivers 429-475 ft-lb (582-644 Nm) of torque, providing robust performance across a range of conditions.
• Compression Ratio: The engine’s compression ratio varies, with 10.9:1 for the SRT models and 10.0:1 for Ram trucks.

Technical Details:

• Engine Weight: The dry weight stands at approximately 500 lbs (227 kg).
• Firing Order: The engine’s firing order is 1-8-4-3-6-5-7-2, ensuring balanced operation.
• Oil Specifications: It requires SAE 0W-40 engine oil, with a capacity of 6.7 liters (7.0 qt) including the oil filter. The recommended oil change interval is every 6,000 miles (10,000 km) or six months.

Applications:

This versatile engine powers a range of vehicles, including the Ram 2500/3500/4500/5500 and Cab Chassis models, as well as high-performance versions of the Dodge Challenger, Charger, Chrysler 300, Jeep Grand Cherokee, and Dodge Durango.

By blending raw power with refined engineering, the 6.4L Hemi Apache stands out as a formidable choice for both commercial and high-performance applications.

What types of vehicles have the 6.4L HEMI engine been used in?

Currently, the 6.4L Hemi is only available in RAM HD trucks paired to either the six-speed 68RFE automatic transmission or the six-speed Aisin-Seiki AS69RC medium-duty truck transmission. However, this powerful engine has found its place in a diverse array of vehicles, showcasing its versatility and performance capabilities.

Vehicles Featuring the 6.4L HEMI Engine

• RAM Trucks: Beyond the HD line, the 6.4L HEMI engine powers models like the RAM 2500, 3500, 4500, and 5500, including Cab Chassis configurations. This makes it a popular choice for heavy-duty applications requiring robust power.
• Dodge Performance Cars:
  • Challenger: Offered in high-performance trims like the SRT8, R/T Scat Pack, and SRT, the Challenger utilizes the 6.4L HEMI for exhilarating performance.
  • Charger: Similarly, the Charger SRT8, R/T Scat Pack, and SRT models benefit from the engine’s robust power output.
• Chrysler and Jeep:
  • Chrysler 300: The SRT8 and SRT versions of the Chrysler 300 deliver premium performance enhanced by the 6.4L HEMI.
  • Jeep Grand Cherokee: In the SRT8 and SRT trims, this engine provides the Grand Cherokee with a significant performance boost.
• Dodge Durango: The Durango’s SRT8 and SRT models also feature the 6.4L HEMI, combining SUV practicality with impressive power.

This engine’s application across such a wide range of vehicles highlights its adaptability and appeal to both performance enthusiasts and those needing reliable power for heavy-duty tasks.

Model-Year Performance Overview: 6.4L HEMI Apache Applications

When looking at how the Gen. III 6.4L HEMI has been implemented across various vehicles, it’s clear that each model and year brings its own performance flair. Here’s a snapshot of key applications, highlighting horsepower and torque figures where they matter most.

Dodge Challenger SRT8 (2011–2014):

• Power: 460 horsepower at 6,000 RPM
• Torque: 470 ft-lbs at 4,200 RPM

Dodge Challenger SRT8 (2015):

• Upgraded to 485 horsepower at 6,100 RPM
• Torque: Peaks at 475 ft-lbs at 4,700 RPM

Jeep Grand Cherokee SRT & Dodge Durango SRT (2015):

• Power: 475 horsepower at 6,000 RPM
• Torque: 470 ft-lbs at 4,300 RPM

RAM 2500/3500 (2014+):

• Power: Ranges from 366 to 410 horsepower at 5,600 RPM (model and configuration dependent)
• Torque: Robust 429 ft-lbs at 4,000 RPM

These figures underscore the engine’s capability to adapt for both hard-working trucks and adrenaline-driven performance cars. The 6.4L HEMI continues to set the standard, offering substantial power and torque tailored to each vehicle’s role and personality.

How does the 6.4 liter truck Hemi engine compare to other modern and classic Hemi engines?

Comparing the 6.4 Liter Truck Hemi to Other Hemi Engines

The 6.4-liter truck Hemi V8, introduced in the 2014 model year, offers a balance of durability, power, and efficiency, specifically designed for heavy-duty applications in Ram pickups and chassis cabs. Here’s how it stacks up against other modern and classic Hemi engines.

Modern Hemi Engines

• 7 Liter Hemi: Known for its versatility across a range of applications, the 5.7 Hemi offers commendable power with 390 horsepower and 407 lb-ft of torque. It’s a popular choice for light-duty trucks.
• 4 Liter SRT Hemi: This performance-oriented variant delivers between 470 and 485 horsepower, alongside 470 to 475 lb-ft of torque, making it suitable for high-performance vehicles. Unlike the 6.4 truck engine, it prioritizes top-end power.
• Supercharged ‘Hellcat’: Setting a high benchmark, the Hellcat variant offers extreme horsepower well beyond the standard Hemis, tailored for performance enthusiasts looking for maximum thrill.

Classic Hemi Engines

• 426 Hemi (“Elephant Engine”): Favored for its legendary status and high performance in muscle cars of the past, this engine remains iconic for enthusiasts and collectors due to its historical significance and raw power.
• 392 Crate Hemi: Known for being a versatile upgrade option for classic car restorations, it captures the essence of the original Hemis while offering improved performance and reliability.

In summary, the 6.4-liter truck Hemi integrates both modern advancements and traditional engineering prowess, standing out with its targeted focus on durability and efficiency tailored for heavy-duty applications while offering a unique comparison to both modern and classic Hemi engines.

How does the ignition system in the 6.4Ltruck Hemi engine work to reduce emissions?

A unique dual-spark system on the engine gives two spark plugs per cylinder, with the coil plug firing the plug it resides over and a wire that runs across the engine to the opposite bank to fire that plug. The extra plug fires during the power stroke to more fully burn the fuel in the cylinder, which provides more power in the down stroke and also numbers the amount of catalyst plates needed in the exhaust system.

This system employs eight coils to fire 16 spark plugs, enhancing combustion efficiency. By igniting the extra plug during the power stroke, the fuel is burned more completely, which not only increases power output but also optimizes the emissions process.

Additionally, this approach allows the primary spark plug to fire closer to top dead center. This precise timing contributes to increased torque and significantly reduces NOx emissions, cutting down on pollutants like ozone. As a result, the ignition system plays a pivotal role in minimizing environmental impact while maximizing engine performance.

What technologies are used in the 6.4 liter truck Hemi engine to improve fuel efficiency?

Featuring a cylinder deactivation system called MDS (multi displacement system), the engine has the ability to shut off fuel in the passenger bank of the engine when power is not needed. This equipment was part of the initial design of the Hemi engine, not an afterthought, so it fully integrates into the engine design.

This improved reliability by reducing complexity and lowered the manufacturing cost. How it works is a hydraulic lifter activates, which cuts off the valve lifters so that there is no loss of energy by pumping air through those cylinders and compressing it. The engine can complete this transition in less than 0.04 seconds, and unless you have superhuman senses, you will never know it is there.

Additionally, the engine employs a cooled EGR (Exhaust Gas Recirculation) system to further enhance fuel efficiency by reducing the engine’s temperature and improving combustion efficiency. This combination of technologies ensures that the engine operates with lower emissions and greater fuel economy.

The engine’s design is robust, featuring a deep-skirt configuration with a cast iron block and a forged steel crank. The main bearing caps are cross-bolted, echoing the design principles found in other high-performance engines. The use of 356 aluminum for the heads contributes to a lighter engine overall, aiding in efficiency without sacrificing durability.

By integrating these technologies from the ground up, the engine achieves a balance of power and efficiency, offering a seamless driving experience that prioritizes both performance and fuel savings.

What design features contribute to the 6.4L truck Hemi engine’s durability and efficiency?

Durability and Efficiency Features

• Deep-Skirt Design: The engine’s deep-skirt design and cast iron block provide a solid foundation, enhancing structural integrity and reducing wear and tear over time.
• Forged Steel Crank & Cross-Bolted Main Bearing Caps: These features further bolster the engine’s toughness, ensuring it can handle heavy-duty usage without compromising performance.
• Advanced Cooling System: With a high-volume oil cooler and computational fluid dynamics, the engine maintains optimal temperatures, essential for both durability and efficiency.
• Variable Valve Timing: The hydraulic cam phasing system, controlled by a computer, offers precise valve timing adjustments, enhancing fuel efficiency and performance.
• Cylinder Deactivation: Known as the Multi Displacement System (MDS), this feature turns off the fuel in four cylinders when not needed, improving fuel economy without sacrificing power. Transitions occur in under 0.04 seconds, showcasing seamless integration and reliability.

These thoughtfully engineered features, from robust materials to innovative systems, ensure the 6.4L Apache not only performs exceptionally but also stands the test of time in demanding conditions.

What materials and design choices are used in the construction of the 6.4L truck Hemi engine?

“Receiving upgrades in the form of tough alloy exhaust valve seats, sodium-filled exhaust valves, aircraft-grade stainless steel gaskets and fasteners, and a high-efficiency and high-flow oil cooling system with piston jets and an oil cooler designed with the aid of computational fluid dynamics. All forged internals, with a cast iron block, cross-bolted main-bearing caps, and 356 aluminum—and the list keeps going and going.

The engine’s design incorporates a deep-skirt block, ensuring structural integrity with a cast iron construction and a forged steel crank. This robust foundation is complemented by heads crafted from 356 aluminum, providing a balance of strength and weight reduction.

Key Construction Details and Specifications

• Block Material: Cast iron, offering long-term durability and torsional strength.
• Displacement: 6.4 liters (391 cubic inches), combining generous bore and stroke for both torque and horsepower.
• Bore Diameter: 4.090″, with a stroke of 3.72″, maximizing cylinder volume while maintaining reliability.
• Deck Height: 9.25″, contributing to the engine’s stoutness and compatibility with high-performance internals.
• Main Cap Design: Two-bolt main caps with additional lateral cross-bolts, enhancing crankshaft stability under load.
• Thrust Bearing Location: Positioned at number 3 for optimal load distribution.
• Bore Spacing: 4.46″, echoing classic V8 proportions yet designed for modern durability.
• Cam-to-Crank Centerline: 7.44″, engineered for precise valvetrain geometry.
• Piston Oil Squirters: Yes, with targeted cooling jets to keep pistons at optimal temperatures under hard use.
• Bellhousing Pattern: Utilizes a familiar small block bolt pattern (with a minor update—top center bolt omitted) for compatibility across a range of applications.

From the material choices—like robust iron for the block and lightweight yet strong 356 aluminum for the heads—to the inclusion of features such as sodium-filled exhaust valves, forged steel crank, and advanced oil cooling passages, every detail is aimed at maximizing both longevity and efficiency.

All these elements combine to create an engine that’s as tough as it is refined, perfectly suited for the rigorous demands of heavy-duty work or spirited driving alike.