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The Ultimate Hemi Showdown: 7 Critical Differences Between The 6.4L (392) And 5.7L V8

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The choice between a 5.7L Hemi and its bigger, more aggressive sibling, the 6.4L Hemi (also known as the 392), is one of the most common and heated debates in the modern Mopar community. As of late 2025, with the internal combustion engine era drawing to a close for many of these models, understanding the core differences is more crucial than ever for buyers looking to invest in a piece of V8 history.

This deep-dive comparison, based on the latest performance data and owner reports, will dissect the two legendary engines across performance, cost of ownership, reliability, and modding potential. Whether you're considering a new Ram 1500 or a used Dodge Challenger, this breakdown will clarify which Hemi V8 truly deserves a spot in your garage.

Engine Specifications: 5.7L vs. 6.4L Hemi V8 at a Glance

The 6.4L (392 cubic inches) is fundamentally a bored and stroked version of the 5.7L (345 cubic inches) Gen III Hemi architecture. This difference in displacement translates directly to significant variations in power output, especially between the popular car applications like the Challenger R/T and the Challenger Scat Pack.

  • Engine Name: 5.7L Hemi V8 (345 CID) vs. 6.4L Hemi V8 (392 CID)
  • Common Applications (Car): Dodge Challenger R/T, Dodge Charger R/T vs. Dodge Challenger Scat Pack, Dodge Charger Scat Pack
  • Common Applications (Truck): Ram 1500 (often with eTorque) vs. Ram 2500/3500 HD
  • Car HP/TQ (Approx.): 370-375 HP / 400 lb-ft TQ vs. 485 HP / 475 lb-ft TQ
  • Truck HP/TQ (Approx.): 395 HP / 410 lb-ft TQ vs. 410 HP / 429 lb-ft TQ
  • Required Fuel (Car): 87 Octane (Automatic) / 89 Octane (Manual) vs. 91+ Octane (Premium)
  • 0-60 MPH (Challenger): Mid-5 seconds vs. Low-4 seconds

1. The Raw Performance Difference: Scat Pack vs. R/T

When comparing the performance car variants—the 5.7L in the Challenger R/T and the 6.4L in the Challenger Scat Pack—the difference is night and day. The 6.4L Hemi delivers an additional 110-115 horsepower and approximately 75 lb-ft of torque.

This power gap places the 6.4L firmly in the 12-second quarter-mile club, while the 5.7L is a strong performer in the 13-second bracket. The larger displacement of the 392 provides a much better torque band and stronger top-end pull, making it feel significantly faster, especially at highway speeds.

2. Fuel and Cost of Ownership: The Octane Penalty

The most significant long-term financial difference between the two engines is their fuel requirement. The 5.7L Hemi, particularly when paired with the popular 8-speed ZF automatic transmission, is designed to run on readily available and cheaper 87 octane regular gasoline.

In contrast, the high-performance car version of the 6.4L Hemi, with its higher compression ratio (up to 10.9:1 in some car variants), explicitly requires premium 91+ octane fuel. While both engines feature the Multi-Displacement System (MDS) for cylinder deactivation to save fuel, the 6.4L will consistently cost more to fill up and will generally yield about 2 MPG less than the 5.7L in real-world driving.

3. Reliability and the Dreaded Hemi Tick

Both Hemi engines are generally considered reliable V8s, with many owners reporting mileage well over 150,000 miles. However, the 6.4L Hemi is more frequently associated with the "Hemi Tick" issue.

The "Hemi Tick" is a common problem often linked to the lifters, camshaft, or the MDS components. While the 5.7L can also experience this, it seems more prevalent and sometimes more severe in the higher-strung 6.4L. Other common issues for the 6.4L include MDS system failures and misfires.

For buyers prioritizing long-term, high-mileage dependability and lower maintenance costs, the 5.7L Hemi has a greater number of high-mileage examples reported by owners, suggesting a slight edge in longevity, and its brake components are typically cheaper than the performance brakes found on 6.4L Scat Pack models.

4. The Forced Induction Factor: Modding Potential

For enthusiasts planning on serious performance upgrades, such as adding a supercharger or turbocharger (known as forced induction), the 5.7L Hemi is often the preferred starting platform.

Why? The pistons in the 5.7L engine are generally considered more robust for handling boost due to the placement of the piston rings. The 6.4L's stock internals are less tolerant of the extreme pressure and heat generated by forced induction. While both engines can be modified, achieving high horsepower numbers (e.g., over 700 HP) with the 6.4L often requires replacing the stock pistons and connecting rods, making the 5.7L a more cost-effective choice for a boosted build.

5. Truck vs. Car: Different Engines, Same Name

It is crucial to note that the 6.4L Hemi found in heavy-duty trucks (like the Ram 2500) is a different engine than the one in the performance cars (Challenger/Charger).

  • 6.4L Truck Hemi (BGE): Features a cast iron block, different piston rods, and a lower 10.0:1 compression ratio for increased low-end durability and towing capability.
  • 6.4L Car Hemi (392 SRT): Uses an aluminum block and higher compression for maximum horsepower output.

The truck 6.4L is designed for work (max towing up to 19,780 lbs), whereas the 5.7L (often paired with the eTorque mild-hybrid system in the Ram 1500) is designed for a balance of power and efficiency (max towing up to 12,750 lbs).

6. The Transmission and Driveline Advantage

The performance gap is not just about the engine; the supporting hardware matters. In the Challenger/Charger lineup, the 6.4L Scat Pack models come standard with a Limited Slip Differential (LSD), which significantly improves traction and performance during hard acceleration and cornering.

The 5.7L R/T models, however, only offer an LSD when equipped with a manual transmission, meaning automatic R/T owners must rely on brake-based traction control or an aftermarket LSD upgrade. Both engines are commonly paired with the excellent ZF-designed 8HP70 8-speed automatic transmission, which is a major performance asset for both.

7. The Daily Driver vs. Weekend Warrior Intention

Ultimately, the best Hemi is the one that fits your driving intention:

  • Choose the 5.7L Hemi if: You prioritize lower running costs, need a reliable daily driver, want to run 87 octane fuel, or plan for future high-horsepower forced induction modifications. The 5.7L is the practical, cost-effective, and highly capable choice.
  • Choose the 6.4L Hemi (392) if: You want maximum naturally aspirated power, crave the thrill of a 12-second quarter-mile car right off the lot, and are willing to pay the premium fuel and maintenance costs for superior factory performance. The 6.4L is the pure performance, weekend warrior option.

The 6.4L is the clear winner in a pure performance contest, but the 5.7L offers a compelling blend of power, affordability, and modding potential that makes it the smarter choice for a budget-conscious enthusiast or a long-term daily driver.

The Ultimate Hemi Showdown: 7 Critical Differences Between the 6.4L (392) and 5.7L V8
hemi 6.4 vs 5.7
hemi 6.4 vs 5.7

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