Introduction to the Mopar Performance 426 Hemi Supercharger Kit

The Mopar Performance 426 HEMI Supercharger Kit is one of the most sought-after upgrades for owners of classic and modern HEMI-powered vehicles. Designed to deliver a significant boost in horsepower and torque, this kit transforms an already formidable engine into a street-legal powerhouse. Whether you are building a restomod, upgrading a modern Challenger or Charger, or completing a crate engine project, this supercharger kit offers a proven path to increased performance without sacrificing reliability.

The kit typically includes a Roots-type supercharger, an intercooler system (on certain variants), a dedicated intake manifold, fuel injectors, a higher-flow fuel pump, and all necessary hardware and gaskets. Installation requires moderate mechanical experience, a well-equipped workshop, and strict adherence to torque specifications. This guide expands on the original instructions, providing detailed, step-by-step procedures that address common challenges and best practices. We will cover everything from workspace preparation to final tuning considerations, ensuring you achieve a safe, leak-free, and powerful installation.

Tools and Materials Needed

Before you begin, ensure you have the following tools and consumables on hand. Using the correct tools prevents damage to fasteners and ensures accurate torque application.

  • Socket set (1/4-inch, 3/8-inch, and 1/2-inch drive), including standard and deep sockets in metric and SAE sizes
  • Combination wrench set (metric and SAE)
  • Torque wrench (3/8-inch and 1/2-inch drive, capable of 10–150 ft-lb range)
  • Screwdrivers (flathead and Phillips, medium and large)
  • Pliers (standard and needle-nose)
  • Shop towels or lint-free rags
  • Engine oil (as specified in your vehicle owner’s manual)
  • Coolant (50/50 mix of distilled water and appropriate antifreeze)
  • Mopar Performance 426 HEMI Supercharger Kit (verify kit number and contents per your application)
  • Replacement gaskets (intake manifold, throttle body, and any other sealing surfaces)
  • Thread locking compound (medium strength, such as Loctite 242)
  • Anti-seize compound for stainless steel bolts
  • Vacuum line and hose assortment (if any lines are damaged during removal)
  • Fuel line disconnect tools (if your vehicle uses quick-connect fittings)
  • Scan tool or code reader (to clear trouble codes after reconnecting battery)

Safety First: Preparing for the Installation

Working on a high-performance engine requires caution. Follow these safety steps before turning any wrenches:

  1. Park on level ground and engage the parking brake. Chock the rear wheels to prevent roll.
  2. Disconnect the negative battery terminal using a wrench. Isolate the cable end with a shop towel to prevent accidental reconnection.
  3. Allow the engine to cool completely — ideally overnight. The supercharger kit installs on the intake valley, which retains heat for hours after shutdown.
  4. Work in a well-ventilated area. Fuel vapors and coolant fumes can accumulate.
  5. Wear safety glasses and nitrile gloves when handling fluids and cleaning solvents.
  6. Keep a fire extinguisher rated for Class B and C within easy reach.

Step 1: Removing Factory Components

To make room for the supercharger, you will remove the air intake system, factory intake manifold, throttle body, and ancillary wiring. Proceed methodically to avoid damaging connectors or hoses.

1.1 Remove the Air Intake System

Loosen the clamps at the throttle body and mass airflow (MAF) sensor. On modern HEMI vehicles, you may also need to unclip the airbox. Gently pull the intake tube free and set it aside. If your vehicle uses a cold-air intake, retain the filter housing for reuse (the kit may include a new filter).

1.2 Disconnect the Throttle Body

The throttle body is attached to the intake manifold with four bolts. Before removing them, disconnect the electrical connector for the throttle position sensor (TPS) and, if equipped, the idle air control (IAC). On drive-by-wire systems, unplug the actuator motor connector. Note the routing of any vacuum lines to the throttle body — label them with tape for reinstallation.

1.3 Remove the Factory Intake Manifold

Begin by unbolting the intake manifold from the cylinder heads. The bolt pattern is typically 18–22 ft-lb on a 426 Hemi. Work in a crisscross pattern to prevent warpage. Carefully lift the manifold straight up, watching for any wiring harnesses or fuel lines that may still be attached. Place a clean shop towel over the intake ports to keep debris out.

1.4 Disconnect Fuel Supply (If Required)

Some supercharger kits require upgrading the fuel rails and injectors. In that case, relieve fuel pressure (locate the Schrader valve on the fuel rail and depress with a rag to release pressure). Disconnect the fuel lines using the appropriate tool. On returnless systems, you may need to swap the fuel pump controller. Refer to the kit instructions for specific fuel system modifications.

With the manifold off, you have excellent access to the spark plugs. Replace them with one heat range colder plugs if the kit suggests it (common for forced induction). Remove the wires or ignition coils, then use a spark plug socket to extract the plugs. Gap the new plugs to the manufacturer's specification (typically 0.035–0.040 inch for boosted applications).

Step 2: Installing the Supercharger Kit

Now you are ready to install the Mopar Performance supercharger. Work slowly, keep sealing surfaces clean, and torque every bolt to specification.

2.1 Prepare the Engine Valley

Thoroughly clean the tops of the cylinder heads and the front and rear intake manifold sealing surfaces. Use a plastic scraper and brake cleaner to remove old gasket material. Inspect the valley for any oil or coolant leaks — address them now. Install the new intake manifold gaskets (supplied in the kit) onto the cylinder heads. Apply a thin bead of RTV silicone at the front and rear China walls if required by the gasket design.

2.2 Mount the Supercharger

Carefully lower the supercharger assembly onto the engine valley. Align the dowel pins with the cylinder head holes. The supercharger should sit flush. Hand-thread the mounting bolts in a star pattern. Then, using a torque wrench, tighten them in three steps to the specified torque (typically 105–115 in-lb or 9–10 ft-lb). Do not overtighten — aluminum threads strip easily.

2.3 Install the Intake Manifold (if separate from supercharger)

Some kits include a separate intake manifold that bolts over the supercharger. Use the provided gasket and apply a thin layer of gasket sealant to the mating surfaces. Tighten the manifold bolts in the correct sequence to the manufacturer’s specification (commonly 18–22 ft-lb).

2.4 Reattach the Throttle Body

Clean the throttle body mating surface. Install a new gasket, then bolt the throttle body to the supercharger inlet. Torque the bolts to 84–108 in-lb (7–9 ft-lb). Reconnect the electrical connectors and vacuum lines per your labeling. If the kit uses a larger throttle body, ensure the accelerator cable (or pedal) travel is sufficient; adjust the cable housing as needed.

Step 3: Reconnecting Systems

With the supercharger installed, you must reconnect cooling, fuel, and electrical systems before startup.

3.1 Cooling System

If your supercharger kit includes an intercooler (air-to-air or air-to-water), you will need to plumb the coolant lines. Use the supplied hoses and clamps. On water-to-air intercoolers, connect the coolant pump and reservoir. Fill the cooling system with fresh 50/50 mix. Bleed air from the system by running the engine with the radiator cap off until the thermostat opens and coolant circulates.

3.2 Fuel System

Reconnect the fuel lines using new O-rings if the quick-connect fittings were disturbed. If the kit includes a fuel pressure regulator, adjust it to the recommended base pressure (usually 58–60 psi for returnless systems). Prime the fuel pump a few times by cycling the key on (without starting) to build pressure. Check for leaks at all connections.

3.3 Electrical and Vacuum Lines

Reconnect all wiring harnesses: mass airflow sensor, throttle position sensor, knock sensors (if relocated), and any boost pressure sensor. Reattach vacuum lines to the supercharger bypass valve, fuel pressure regulator, and boost reference ports (for the blow-off valve or wastegate on larger kits). Use a vacuum pump to verify no leaks: connect the pump to the manifold vacuum port and watch for a steady reading. Repair any cracked or brittle hoses.

3.4 Serpentine Belt and Tension

Some supercharger kits require a longer belt and a modified tensioner. Install the new belt per the routing diagram provided. Manually rotate the crankshaft one full turn to ensure the belt tracks correctly and no pulleys bind. Check belt tension — it should deflect about 1/2 inch at the longest span between pulleys.

Step 4: Final Checks and First Start

Before turning the key, inspect every connection and fastener.

4.1 Double-Check Torque

Re-torque the supercharger mounting bolts, intake manifold bolts, throttle body bolts, and any fuel rail bolts. Use a torque wrench to ensure you haven’t missed any critical fasteners.

4.2 Reconnect Battery and Prime

Reconnect the negative battery terminal. Turn the key to the ON position (without starting) for three seconds, then OFF. Repeat twice to prime the fuel pump and let the ECU adapt to the new sensors. On modern vehicles, perform a throttle body relearn procedure if specified by the manufacturer (often: key ON, press accelerator pedal to the floor, hold for 10 seconds, then release).

4.3 Start the Engine

Start the engine and let it idle. Listen for any abnormal whining (belt slippage) or ticking (exhaust leaks). Initially, the engine may run rough as the ECU adjusts to the increased airflow and fuel trims. Allow it to reach operating temperature. Check the dash gauges: oil pressure, coolant temperature, and boost (if a gauge is installed).

4.4 Leak Check

With the engine running, inspect all coolant hoses, fuel line connections, and vacuum lines for leaks. Spray a small amount of carburetor cleaner around the intake gaskets — if idle speed changes, you have a vacuum leak. Fix any issues immediately.

4.5 Test Drive and Tuning

Perform a short test drive at low load, gradually increasing throttle. Monitor boost levels (not exceeding the kit’s maximum – typically 6–9 psi on a stock internal Hemi). If your vehicle uses a standalone ECU or a piggyback tuner, you will need a professional dyno tune to optimize air/fuel ratios and ignition timing. Even with a pre-programmed chip, it is wise to log data on the first drive and adjust fuel pressure or boost cut if necessary.

Post-Installation Tips and Maintenance

  • Oil change: After the first 500 miles, change the engine oil and filter. Forced induction generates more heat and can lead to fuel dilution in the oil. Use a high-quality synthetic oil with the correct viscosity (commonly 5W-30 or 5W-40).
  • Spark plug gap: Check spark plug gap again after 1,000 miles. Boosted engines can close gaps over time; re-gap if needed.
  • Belt inspection: Examine the supercharger belt every 3,000 miles for cracking or glazing. Replace as needed.
  • Intercooler maintenance: If you have an air-to-water intercooler, check the coolant level monthly. Flush and replace every two years.
  • Fuel quality: Always use premium unleaded gasoline (93 octane or higher) to prevent detonation. For high-boost applications, consider using ethanol blends (E85) with appropriate fuel system upgrades.
  • Professional tuning: Even if the kit includes a “plug and play” tune, we recommend a custom dyno calibration by a certified engine tuner. This ensures the engine runs safely at wide-open throttle and maximizes power output.

Conclusion

Installing the Mopar Performance 426 HEMI Supercharger Kit is a rewarding project that delivers a dramatic increase in power and driving excitement. By following this expanded guide, you have the detailed steps, torque values, and inspection procedures necessary to complete the job correctly. Remember that attention to detail during the mechanical installation — especially gasket sealing and fuel system connections — will prevent costly problems later. For further reading, consult the official Mopar Performance website for kit-specific documentation and consider reviewing a 426 HEMI technical overview to understand the engine’s capabilities. If you encounter any tuning challenges, resources such as HP Tuners or a local performance shop can provide calibration support. With careful work and proper maintenance, your supercharged 426 HEMI will provide reliable, exhilarating performance for years to come.