Understanding the 6.4L HEMI: The Foundation for 600+ HP

The 6.4L HEMI, often called the 392 HEMI, is a modern marvel of Chrysler engineering. Part of the third-generation HEMI family, this 392-cubic-inch V8 blends classic pushrod simplicity with advanced variable valve timing (VVT) and the Multi-Displacement System (MDS). Its robust cast-iron block and forged steel crankshaft provide the strength needed to handle forced induction, while the aluminum cylinder heads with hemispherical combustion chambers promote efficient airflow and high compression. In stock form, the 6.4L delivers 485 horsepower and 475 lb-ft of torque in the Dodge Challenger and Charger. However, with the right supercharger kit, like the Mopar Stage 3 Blower Kit, crossing the 600-horsepower mark is not only achievable but reliable.

Key Differences from the 5.7L HEMI

While the 5.7L HEMI is a great engine, the 6.4L offers several critical advantages for high-horsepower builds. The 6.4L features a larger bore (4.09 inches versus 3.92) and a longer stroke (3.72 inches versus 3.58), giving it a substantial displacement advantage. It also uses larger intake and exhaust valves, a higher-lift camshaft, and stronger connecting rods rated for higher cylinder pressures. The MDS system in the 6.4L is also more refined, deactivating four cylinders under light load to improve fuel economy without sacrificing durability. These differences make the 6.4L a far better candidate for a stage 3 supercharger upgrade.

The Mopar Stage 3 Blower Kit: What You Get

The Mopar Stage 3 Blower Kit (part number P5155802) is an OEM-engineered supercharger system designed specifically for the 6.4L HEMI in 2015+ Dodge Challenger, Charger, and Chrysler 300 models. Unlike aftermarket kits that require extensive fabrication, this kit bolts on using factory mounting points and includes everything needed to add 130–150 horsepower to the wheels. The kit comprises a Roots-type supercharger (based on the Hellcat design but with unique tune to match the 6.4L’s compression ratio), a large air-to-water intercooler, high-flow fuel injectors, a performance calibration via the Mopar PCM flash, and all necessary hardware. The result is a drive-by-wire system that retains all factory features like cruise control, electronic stability control, and MDS operation.

Power Gains and Real-World Performance

With the Mopar Stage 3 Blower Kit properly installed and the included calibration, a 6.4L HEMI typically produces 610–640 horsepower at the crank on 91-octane pump gas. On the dyno, that translates to about 520–550 rear-wheel horsepower, a significant jump from the stock 385–405 whp. Torque also increases dramatically, climbing to around 570–600 lb-ft at the wheels. This is enough to propel a 4,000-pound Challenger into the low 11-second quarter-mile range at over 120 mph. The kit's air-to-water intercooler keeps intake temperatures manageable, allowing consistent performance even in warm weather conditions.

Installation: A Step-by-Step Deep Dive

While the Mopar Stage 3 Kit is designed for a straightforward installation, it still requires mechanical proficiency and attention to detail. Plan for a full weekend in a well-equipped garage. Below is an expanded guide that covers the critical phases.

Pre-Installation Preparation

  • Disconnect the battery negative terminal and wait 10 minutes to allow the PCM capacitors to drain.
  • Drain the engine coolant to prevent spillage when removing the thermostat housing.
  • Remove the engine cover, the factory intake manifold, and the air intake box. Label all connectors and vacuum hoses.
  • Remove the throttle body (it will be reused with the kit).
  • Remove the factory fuel rail and injectors. The kit includes higher-flow injectors, so set the stock ones aside.

Installing the Supercharger

  • Remove the four spark plugs to prevent engine damage during cranking if a piston accidentally hits a valve later (unlikely but good practice).
  • Install the provided intercooler brick into the intake valley, ensuring the O-rings are lubricated with coolant. Torque the intercooler bolts to spec (typically 10 ft-lbs).
  • Place the supercharger onto the intake manifold, using new gaskets. The kit includes a special spacer plate to align the supercharger drive pulley with the engine’s crankshaft pulley.
  • Install the supercharger drive belt. The kit provides a specific belt length; do not substitute.
  • Reattach the throttle body to the supercharger inlet. Use a new gasket.

Fuel System and Electrical

  • Install the included 65 lb/hr fuel injectors into the fuel rail. Ensure the O-rings are seated and lubricated with gasoline.
  • Connect the fuel rail to the intake manifold. Torque the rail bolts to 7 ft-lbs.
  • Route the intercooler coolant lines from the pump (included) to the intercooler brick. Use the provided hose clamps.
  • Fill the intercooler system with a 50/50 mix of distilled water and antifreeze. Bleed air by running the pump with the reservoir cap off.

Calibration and Final Checks

  • Install the Mopar PCM flash. This is a plug-and-play module that connects to the OBD-II port; do not start the engine until the flash is complete.
  • Reinstall all components removed earlier, including the spark plugs. Use the colder heat range plugs (NGK LFR6AHX or equivalent) that come with the kit.
  • Reconnect the battery and check for any loose wires, vacuum leaks, or coolant drips.
  • Prime the fuel system by turning the key to ON (without starting) three times, waiting 5 seconds each time. Start the engine and let it idle for 10 minutes, monitoring for odd noises or dashboard warning lights.

Tuning the Supercharged 6.4L HEMI

The Mopar Stage 3 Blower Kit comes with a factory-calibrated PCM that is optimized for 91-octane fuel and the hardware included. However, many owners choose to go beyond the base calibration for even more power or to address specific driving conditions. Here’s what you need to know about tuning.

Why Custom Tuning Beats the Factory Calibration

The factory flash is conservative. It intentionally keeps timing low and fuel rich to protect the engine across all climates and altitudes. A professional dyno tune can safely add 20–30 horsepower by advancing ignition timing and leaning out the air-fuel ratio to around 11.8:1 at wide-open throttle. Additionally, a custom tune can improve part-throttle drivability, sharpen throttle response, and disable MDS if desired (though MDS is fine with the kit). Tuning is especially recommended if you plan to run ethanol blends like E85, which can boost power beyond 650 hp.

Available Tuning Platforms

  • Mopar PCM Flash (included): Provides a safe, warranty-friendly calibration. Works with 91 octane and standard fuel systems.
  • DiabloSport Trinity 2 or i3: Allows you to adjust fuel and timing maps, and data-log. Requires a custom tune file from a reputable tuner.
  • HP Tuners: The choice of elite builders. Allows full control of the stock PCM (no aftermarket ECU needed). Requires professional knowledge or remote tuning service.

Supporting Mods for Higher Output

If you’re aiming for 650+ horsepower, consider these upgrades alongside the Stage 3 Kit:

  • Upgraded fuel pump: A drop-in fuel pump module (e.g., from Fore Innovations or DW) ensures adequate fuel delivery at higher boost levels.
  • Larger injectors: 80 lb/hr or 100 lb/hr injectors if running E85.
  • High-flow exhaust: A cat-back system reduces backpressure and helps the engine breathe. Avoid headers unless you also install a custom tune to address lean conditions.
  • Cold air intake: The Mopar kit includes a low-restriction intake, but an aftermarket enclosed cold air system can lower intake air temperatures slightly.

Maintenance for Long-Term Reliability

A supercharged 6.4L HEMI demands diligent maintenance. Follow these guidelines to keep the Mopar Stage 3 Kit performing for tens of thousands of miles.

Oil and Fluid Changes

  • Change engine oil every 3,000–5,000 miles using 5W-30 full synthetic. The supercharger adds heat and stress to the oil.
  • Check the intercooler coolant level monthly. Replace the coolant every 2 years.
  • Inspect the supercharger drive belt for cracks or glazing every 10,000 miles. Replace as needed.

Blower-Specific Service

The Mopar Stage 3 supercharger uses a sealed bearing design that does not require oil changes like older units. However, the internal gears and bearings should be inspected by a specialist after 30,000–40,000 miles. The supercharger’s rotor pack can accumulate carbon deposits; a professional cleaning every 50,000 miles can restore efficiency. Also, listen for any whining noise that changes with throttle—this could indicate a failing bearing.

Spark Plugs and Ignition

Supercharged engines generate higher cylinder pressures, which can foul spark plugs more quickly. Replace the colder heat range plugs every 15,000 miles. Use the specified NGK or Champion plugs; do not extend the gap beyond 0.035 inches. The increased power also strains the coil packs—replace any coil that shows signs of misfire.

Monitoring Performance

Install a wideband air-fuel ratio gauge and boost gauge to monitor engine health in real time. If you see air-fuel ratios leaner than 12.5:1 at wide-open throttle, reduce load immediately and investigate boost leaks or fuel pressure issues. Regularly check for check engine lights; many aftermarket tunes will log counts of knock retard. Keep logs and share them with your tuner during periodic checkups.

Conclusion: Building a 600+ HP Beast

The .7 HEMI (6.4L) with the Mopar Stage 3 Blower Kit is a proven path to 600+ horsepower without sacrificing daily drivability. The OEM engineering of the kit ensures a level of reliability that backyard builds often lack. Combined with proper installation, a custom tune, and responsible maintenance, your supercharged 6.4L HEMI will deliver thrilling acceleration and reliable performance for years. Whether you use it for street driving, drag racing, or track days, the Mopar Stage 3 Kit transforms your HEMI into a powerhouse that can hang with exotic machinery. For more details on the kit, visit the official Mopar website. For tuning support, consult professionals at Hemifever or Injected Engineering. And remember: always prioritize safety and quality components to protect your investment.