How much HP can you get out of a 6.4 Hemi?

The 6.4 Hemi, often referred to as the 392, typically produces about 470-485 horsepower from the factory, with substantial gains available through careful tuning and modification. In short, you can move from stock levels into a broad range depending on how far you’re willing to go—from bolt-ons that lift horsepower modestly to forced induction that pushes well past the 700-horsepower mark.

Understanding the 6.4 Hemi

The 6.4 Hemi is a naturally aspirated V8 displacing 6.4 liters (392 cubic inches). It’s used in high-performance variants of several Stellantis models, notably the Challenger and Charger in the SRT 392 lineup, as well as the Jeep Grand Cherokee SRT and the Durango SRT. Engine builders and enthusiasts often refer to it as the “392 Hemi.” Horsepower figures have evolved slightly over the years due to tuning, emissions requirements, and minor mechanical updates, but the core power target has hovered in the mid- to upper-400s for most modern applications.

Stock horsepower: by model and year

Below is a quick overview of typical stock horsepower figures for common 6.4 Hemi applications. The numbers refer to horsepower at the crank; real-world wheel horsepower will be lower due to drivetrain losses.

• Challenger SRT 392 (early 2011–2014): about 470 hp


• Challenger/Charger SRT 392 (2015 onward): about 485 hp


• Jeep Grand Cherokee SRT (2012–2018): around 470 hp


• Durango SRT (2012–2018): around 470 hp

Notes: The 6.4 Hemi shares its core architecture across these platforms. The high-boost, track-focused Hellcat variants use a different engine family (supercharged 6.2L in the Trackhawk, for example), so those power figures are not representative of the naturally aspirated 6.4 family.

Power gains from modifications

With the 6.4 Hemi, horsepower gains depend on whether you stay NA (naturally aspirated) or add forced induction, along with supporting upgrades to fuel, cooling, and the drivetrain. The following breakdown gives a sense of typical outcomes, but individual results vary by condition, fuel, and tuning accuracy.

• Naturally aspirated bolt-ons and tuning



• Gains: roughly 20–60 hp above stock, depending on parts and tuning quality


• Notes: common components include cold-air intake, improved exhaust (cat-back or headers), high-flow catalysts, and a dyno tune. Expect the wheel horsepower to be about 15–25% lower than crank horsepower due to drivetrain losses.

These NA gains are the most approachable route for enthusiasts who want more snap from a stock 6.4 without major internal changes.

• Cam/valve-train work and head porting



• Gains: roughly 50–150 hp NA, depending on the quality of the cam profile, springs, and port work


• Notes: significant cam swaps and head work require proper matching components and tuning. These alterations can alter idle characteristics and emissions behavior.

For a substantial NA upgrade, expect a broader, more aggressive power curve and the need for supporting hardware and fuel calibration.

• Forced induction (supercharger or turbocharger)



• Gains: commonly in the 600–900+ crank horsepower range with proper fueling and cooling


• Notes: this path usually requires a built or upgraded bottom end, fuel-system upgrades (injectors, pump, rails), intercooling, transmission and drivetrain considerations, and meticulous tuning. Real-world results depend heavily on the kit, boost level, octane fuel, and reliability goals.

Forced-induction builds are the most dramatic way to increase output, but they demand careful engineering and ongoing maintenance. Expect substantial changes to cooling requirements, oiling strategy, and drivetrain durability.

Practical considerations when boosting a 6.4 Hemi

Turning a 6.4 Hemi into a high-horsepower machine isn’t just about the engine. Proper cooling, fuel delivery, transmission strength, and suspension handling matter just as much. In addition, aftermarket support, warranty implications, and local emissions requirements should influence your plans. A well-considered build often involves a staged approach: start with reliable NA gains, assess street use vs. track goals, then consider forced induction if you’re seeking extreme performance.

Summary

In stock form, the 6.4 Hemi produces roughly 470–485 hp depending on model and year. With bolt-ons and a tune, you can realistically add 20–60 hp. More extensive upgrades, including cam work and head porting, can push NA power higher—on the order of 50–150 hp more. For dramatic gains, forced induction is the common route, with typical targets in the 600–900+ hp range, depending on the build, fueling, and cooling systems. If you’re considering a project, plan for a careful, staged approach to balance power, reliability, and daily usability.

How much boost can a 6.4 L Hemi handle?

A stock 6.4L Hemi can handle about 5-8 PSI of boost before needing internal engine upgrades, with a higher compression ratio making it more sensitive than the 5.7L. Exceeding this limit risks engine failure, but with supporting modifications like forged pistons and rods, it can handle 11-15 PSI or more. For reliable power, it's best to stay within the lower end or invest in a forged bottom end. 
This video discusses the limitations of the 6.4L Hemi when boosted and the risks of not upgrading the internals: 42sTorqueSavvyYouTube · Nov 7, 2025
Boost levels and engine limitations 

• Stock engine: A stock 6.4L is generally safe up to 5-8 PSI. However, its high compression ratio makes it more susceptible to knock, so using quality fuel or E85 is crucial even at these levels. 
• Exceeding stock limits: Pushing beyond 8 PSI on a stock engine is risky and can lead to catastrophic failure. The stock internals are not designed for this level of stress. 
• Engine with forged internals: With a forged pistons and rods, the engine can safely handle higher boost, often in the 11-15 PSI range. Some builds with forged components have safely pushed higher, but this requires a thorough, well-executed tuning process. 

What to consider

• Fuel quality: A 6.4L requires a higher-octane fuel or an E85 blend to safely run boost due to its high compression ratio. 
• Transmission: The factory transmission will also become a weak link at higher power levels and will need to be upgraded for reliable performance. 
• Tuning: A proper tune is essential for any boosted application, regardless of boost level, to ensure the engine runs safely and efficiently. 
• Intended use: The level of boost you can handle depends on your goals. For a reliable street car, sticking to lower boost with supporting mods is the safest bet. For drag racing or other high-performance applications, a fully built engine with forged components is necessary. 

This video demonstrates a 6.4L Hemi build with forged internals and higher boost levels: 56sJohn PartsYouTube · Sep 22, 2022

Can you supercharge a 6.4 L Hemi?

Yes, you can supercharge a 6.4L HEMI, with many aftermarket companies like ProCharger, Whipple Superchargers, and Magnuson Superchargers offering complete, bolt-on kits that can add over 200 horsepower on pump gas without needing internal engine modifications. For higher boost levels, you will need to upgrade internal components like the pistons and rods to ensure durability, as the stock 6.4L HEMI can handle only moderate boost before internal failure occurs. 
This video explains the potential power gains from supercharging a 6.4L HEMI: 56sProCharger SuperchargersYouTube · Jun 27, 2023
Moderate boost (stock internals)

• A stock 6.4L HEMI can handle moderate boost levels with a well-engineered, complete kit, such as a ProCharger system. 
• These kits are designed to be reliable on stock engines and often include an intercooler to reduce detonation risk. 
• With a system like ProCharger's, you can expect power gains of over 215 horsepower on 93 octane gas. 
• For optimal safety, some sources recommend staying under 5-7 pounds of boost when using stock internal components, notes a Reddit post. 

High boost (internal upgrades needed) 

• If you plan to run higher boost levels (e.g., 10+ PSI), you will need to upgrade the internal components of the engine. 
• The pistons and connecting rods are the weakest link in the stock engine and will fail under high boost without an upgrade. 
• Upgrading to forged internal components is necessary for high-horsepower builds. 
• Some experts suggest that if you plan a significant build, you might as well start with a Hellcat engine, as the cost of building a 6.4L to handle extreme boost can approach that of a used Hellcat. 
• There are kits available from companies like Whipple and Magnuson that are designed for either stock or built engines. 

This video shows a supercharged 6.4L HEMI with internal upgrades: 51sR/T LifeYouTube · Apr 26, 2021

Can a 6.4 Hemi be tuned?

Yes, you can tune a 6.4L HEMI engine, and it is a popular modification to improve performance, throttle response, and drivability, especially when combined with bolt-on parts like cold air intakes and headers. Tuning involves rewriting the engine's control unit (ECU/PCM) using specialized hardware and software, with options ranging from pre-loaded tunes on a handheld device to custom, professional tuning. For 2015+ Dodge/Chrysler/Jeep vehicles, an engine control module (PCM) unlock is often required before tuning can be performed. 
Tuning methods and products

• Remote tuning devices: Many companies offer handheld remote tuning devices (like the RTD) that allow you to load pre-loaded tunes for different fuel octanes (e.g., 87, 91, 93). 
• Custom tuning platforms: Tools like HP Tuners allow for professional or custom tuning, where you can either work with a tuner or learn to tune yourself using a combination of software and hardware. 
• PCM unlock service: Vehicles from 2015 and newer often require a PCM unlock service to allow for tuning via the OBDII port. This typically involves sending your PCM to a company for a one-business-day unlock. 
• Combined packages: Some companies offer complete tuning packages that include the necessary hardware, software, and the PCM unlock service, often with support for various modifications like headers and superchargers. 

Benefits of tuning

• Improved performance: Tunes can increase horsepower and torque, with some achieving gains of up to 30+ horsepower and 30+ torque on a mostly stock vehicle. 
• Enhanced drivability: You can expect improved throttle response, quicker shifting, and modified fan settings for reduced heat soak. 
• Customization: Depending on the tune, features like raising the top speed limiter, raising the rev limiter, and disabling the Multi-Displacement System (MDS) are often possible. 

Important considerations

• Warranty: Tuning your vehicle may void the factory warranty for any modifications related to the engine control module. 
• PCM unlock: As mentioned, newer vehicles may require a PCM unlock before tuning. 
• Stage-specific tunes: For vehicles with performance modifications, such as headers or intake kits, you may need a specific tune designed for that level of modification (e.g., Stage 1 vs. Stage 2). 

How much horsepower can a 6.4 Hemi handle?

A stock 6.4L Hemi can handle about 650 horsepower, but internal upgrades are required for significantly more power. The engine can be pushed past 500 horsepower with natural aspiration (N/A) modifications like cold air intakes, and can achieve over 700 horsepower with forced induction like a supercharger, or even over 950 horsepower with comprehensive internal upgrades. 
Stock vs. modified

• Stock: From the factory, the 6.4L Hemi produces between 470 and 485 horsepower. The stock connecting rods and crankshaft are generally considered reliable up to about 650 horsepower. 
• Natural Aspiration (N/A): With bolt-on modifications like a cold air intake and a new camshaft, the 6.4L Hemi can reliably reach approximately 500 to 525 horsepower. However, for higher horsepower numbers, you will need to upgrade components like the throttle body, intake manifold, and camshaft, as well as retune the engine. 
• Forced Induction: Forced induction, such as a supercharger, is the most common way to significantly increase horsepower. 
  • Supercharger: Installing a supercharger can increase horsepower to over 700 hp, even on pump gas. 
  • Twin Turbos: A twin-turbo setup can help the 6.4L Hemi reach over 950 hp. 
• Internal Upgrades: To handle power above 650 horsepower, the 6.4L Hemi engine's internals need to be upgraded. This includes replacing the stock connecting rods with forged ones and using forged pistons. 

Important considerations

• Reliability: Even with upgrades, components can fail. Choosing quality parts and having the work performed by a reputable shop are crucial for building a reliable engine. 
• Crank vs. Wheel horsepower: Crank horsepower (hp) is measured at the engine's crankshaft, while wheel horsepower (whp) is the power delivered to the wheels after accounting for drivetrain losses. A 6.4L Hemi that produces 500 whp is making roughly 600 hp at the crank. 

For more information on building a 6.4L Hemi, consult resources like Summit Racing or HOT ROD Network.