Adding forced induction to a naturally aspirated engine is one of the most effective ways to unlock serious horsepower, and the Subaru WRX is an ideal platform for a centrifiugal supercharger upgrade. The 1.9-liter ProCharger kit is engineered to deliver a clean, linear power curve while providing up to 150 rear-wheel horsepower (RWHP) gains on a stock or lightly modified WRX. Unlike turbochargers that rely on exhaust gases, a belt-driven supercharger provides instant throttle response and consistent boost throughout the rev range. This guide covers the complete installation process for a 1.9L ProCharger on a Subaru WRX, including required tools, step-by-step mounting, fluid connections, and critical tuning considerations. Whether you are a seasoned DIY mechanic or a first-time builder, following these instructions carefully will help you achieve reliable performance gains without cutting corners.

Tools and Materials Needed

Before starting, assemble all necessary tools and components. The ProCharger kit includes the supercharger unit, mounting brackets, pulley system, belt, intercooler, intake piping, and hardware. You will also need the following:

  • Complete 1.9L ProCharger kit (model specific to your WRX year and engine code, e.g., EJ205 or EJ255)
  • Socket set (metric 8mm–19mm, including deep sockets)
  • Combination wrenches (metric)
  • Torque wrench (ft-lb and in-lb ranges)
  • Electric drill with step drill bits and hole saw (for oil return line if required)
  • Vacuum gauge and boost leak tester
  • Engine coolant (OEM spec) and synthetic engine oil (5W-30 or as recommended)
  • Safety glasses and mechanic’s gloves
  • Jack stands and floor jack (to lift the vehicle for undercar access)
  • Shop rags and a drip pan
  • Factory service manual for torque specifications and bolt grades

Pro tip: Check the kit’s instruction sheet for any specific sealants or thread lockers (e.g., Loctite 242) needed during installation.

Preparation Steps

Proper preparation reduces the risk of mistakes and ensures that the installation proceeds smoothly. The WRX engine bay is compact, so taking the time to clear the area and protect sensitive components is essential.

1. Park and Cool the Engine

Move the car to a level, well-ventilated workspace. Engage the parking brake and place wheel chocks behind the rear tires. Allow the engine to cool completely—at least 2 hours after the last drive. A hot engine can cause burns and makes plastic components brittle.

2. Disconnect the Battery

Using a 10mm wrench, remove the negative (black) terminal from the battery. Isolate the cable end with electrical tape to prevent accidental contact. This step eliminates the risk of electrical shorts and protects the ECU while working.

3. Remove the Engine Cover and Air Intake System

Unbolt the plastic engine cover (usually four 10mm bolts). Then remove the factory air intake assembly, including the air filter box, MAF sensor housing, and intake duct. Label the MAF sensor connector and set the sensor aside carefully—it will be reused.

4. Drain Coolant (if Required)

Some ProCharger kits route coolant lines through the throttle body or require removal of the radiator fan. To avoid spills, drain the radiator into a clean container. Open the petcock on the bottom of the radiator and loosen the radiator cap to allow flow. Refill with fresh coolant later.

5. Inspect Belt Tensioner and Pulleys

Check the factory serpentine belt tensioner for smooth operation. A worn or noisy tensioner should be replaced before installing the ProCharger, as the supercharger places additional load on the accessory drive system.

Installing the ProCharger System

This section covers the mechanical installation of the supercharger, intercooler, and piping. Work methodically and torque all fasteners to the values specified in the kit manual.

1. Mount the ProCharger Bracket

Remove the passenger-side strut tower brace (if equipped) to access the mounting area. Clean the mounting surface on the engine block using a degreaser and rag. Position the steel bracket over the supplied studs or bolts. Apply a drop of medium-strength thread locker to each bolt, then hand-tighten. Torque them to the manufacturer’s specification (typically 35–45 ft-lb for M10 bolts). Double-check that the bracket is flush against the block and does not interfere with the alternator or power steering pump.

2. Install the ProCharger Unit

Lift the supercharger head unit into place on the bracket. The unit is heavy (approximately 20–25 lbs), so use a second set of hands or a transmission jack to support it. Align the mounting holes and insert the provided bolts. Tighten in a cross pattern to 25–30 ft-lb. Rotate the supercharger snout by hand to ensure the internal gears turn freely—any binding indicates misalignment.

3. Connect the Intake Piping and Air Filter

Attach the silicone hose from the supercharger outlet to the intercooler inlet. Use T-bolt clamps and tighten to 5–6 inch-lbs (do not overtighten on silicone). Install the MAF sensor into the designated section of the intake tubing, ensuring the arrow points in the direction of airflow. Secure the large conical air filter on the inlet side of the supercharger, positioning it away from hot engine components and the radiator fan.

4. Mount the Intercooler

Remove the factory intercooler (if applicable) or the plastic shroud in front of the radiator. The ProCharger kit includes a high-flow bar-and-plate intercooler. Mount it using the supplied brackets, keeping it parallel to the radiator core with at least ½ inch of clearance. Connect the boost tubes from the supercharger to the intercooler and from the intercooler to the throttle body. Use supplied couplings and ensure that no metal edges contact the silicone—add heat-shrink tubing over sharp edges if needed.

5. Install the Boost Control System

Most 1.9L ProCharger kits include a mechanical boost controller or a wastegate to regulate boost pressure. Mount the boost control solenoid (if electronic) in a location protected from rain and heat, such as the inner fender or firewall. Route the vacuum line from a manifold source (use a dedicated port on the intake manifold, not the brake booster) to the controller, then to the wastegate actuator. Use nylon or silicone vacuum line and secure it with zip ties every 6 inches.

6. Connect the Oil Feed and Return Lines

The 1.9L ProCharger is gear driven and requires its own oil supply. The kit includes a feed line that taps into an oil pressure port on the engine block (usually near the oil filter) and a return line that drains into the oil pan.

  • Oil feed: Remove the plug from the designated oil port. Install the supplied adapter with a copper washer. Attach the stainless steel braided feed line using an AN fitting. Tighten to 15–20 ft-lb.
  • Oil return: Drill a ½-inch hole in the oil pan (above the oil level). Deburr the hole and tap it if required, or use a weld-on bung. Install the return fitting with a rubber grommet and clamp. Connect the return line from the supercharger to this fitting with a slight downward slope. A blocked return line will cause the supercharger to leak oil from the front seal.

7. Install the Drive Belt and Tensioner

Remove the factory serpentine belt. Install the new, longer belt provided in the kit, routing it around the supercharger pulley and the crank pulley, water pump, alternator, and tensioner. Use a belt tension gauge—tension should be 90–120 lbs of force for a new belt. Hand-rotate the engine using a socket on the crankshaft bolt to confirm the belt tracks correctly on all pulleys.

8. Reconnect Coolant Hoses and Refill Fluids

If you removed the radiator hoses or throttle body coolant lines during the install, reconnect them using new clamps. Fill the cooling system with a 50/50 mix of Subaru approved coolant and distilled water, following the factory bleed procedure (warm up engine with heater on, then top off). Replace the oil with fresh synthetic oil and a new filter—the oiled air filter on the ProCharger will contaminate the oil quicker, so an oil change at this stage is wise.

9. Final Mechanical Checks

Before reconnecting the battery, inspect all bolts, clamps, and connections. Verify that the intercooler piping does not contact the hood or other components. Zip-tie any loose wiring away from moving parts. Reinstall the engine cover (if it still fits) and strut tower brace.

Electrical and Tuning Considerations

A mechanical installation is only half the battle. To safely achieve 150 HP gains, the engine management system must be recalibrated to accommodate the increased airflow and boost pressure.

ECU Tuning

Do not start the engine expecting the stock ECU to compensate. The ProCharger will produce approximately 6–8 psi of boost on a stock WRX. Even with low boost, the air/fuel ratio, ignition timing, and fuel delivery must be adjusted. Options include:

  • Open-source tuning (e.g., RomRaider or EcuTek with a tuner): Most cost-effective but requires a competent tuner and a wideband O2 sensor.
  • Plug-and-play piggyback system: Some kits include a fuel controller, but this is not ideal for precise control. Full standalone ECU (e.g., Haltech, Link, or AEM) recommended for maximum safety and performance.

EcuTek is a common choice for Subaru tuners because it retains factory features while allowing custom maps.

Boost Leak Testing

After the initial startup, pressurize the intake system to 10 psi using a boost leak tester (a cap with a Schrader valve that fits the intake hose). Use a spray bottle with soapy water to check for bubbles at all couplers, BOV, and throttle body gaskets. Any leak will cause erratic idle and poor boost response.

Fuel System Upgrades

To support 150 extra horsepower, the stock injectors and fuel pump may be insufficient. Upgrade to high-flow injectors (e.g., 800 cc/min or larger) and a 255 or 340 LPH in-tank fuel pump. DeatschWerks offers drop-in pumps compatible with WRX fuel hangers.

Post-Installation Checks and Break-In

Once the engine starts, follow these steps to ensure everything operates correctly.

Initial Startup Procedure

  1. Reconnect the battery negative terminal. Double-check that all tools and rags are removed from the engine bay.
  2. Prime the oil system by disconnecting the fuel pump relay (or crank fuse) and cranking the engine for 10 seconds. Reconnect and start the engine.
  3. Let the engine idle at around 1,000 RPM. Listen for any unusual knocking, belt chirps, or whistling. A slight supercharger whine is normal—a loud grating noise indicates a problem with the gear drive or oil supply.
  4. Check for oil and coolant leaks around the supercharger, intercooler, and radiator.
  5. Monitor the wideband air/fuel ratio display—should be around 14.7:1 at idle. If it is leaner than 15:1, do not rev the engine; investigate a vacuum leak.

Bedding the Belt

After 5–10 minutes of idling, shut off the engine and recheck belt tension. A new belt will stretch slightly. Retension if necessary. Also check the supercharger oil level (the head unit has a small sight glass or dipstick).

Test Drive Protocol

Take the car on a low-load drive (avoid full throttle) for the first 15–20 miles. This allows the ECU to adapt and the belt to seat. Then perform a few moderate acceleration pulls (2,500–4,500 RPM) while monitoring boost pressure and AFR. If boost exceeds the target (usually 7 psi on a stock engine), reduce wastegate preload or consult the tuner. Full-throttle pulls above 5,000 RPM should only be attempted after a professional dyno tune.

Maintenance and Reliability Tips

Adding a ProCharger increases stress on engine internals, particularly the pistons, rods, and bearings. A stock EJ205 or EJ255 can handle 6–8 psi reliably if the tune is safe and the intercooler is efficient. However, consider these long-term care steps:

  • Change the engine oil every 3,000 miles or 3 months, whichever comes first. Contaminants from blow-by and heat degrade oil faster.
  • Inspect the supercharger oil every oil change. The gear case requires specific ProCharger oil (usually 5 weight). Replace every 30,000 miles.
  • Clean the air filter every 5,000 miles (if oiled foam, use the included cleaning kit). A dirty filter restricts airflow and increases intake temperatures.
  • Check belt condition monthly. A frayed or glazed belt can snap and take out the timing belt or other accessories.
  • Upgrade the intercooler for track use: If you plan to road race or drive in hot climates, consider a larger air-to-water system or a front-mount intercooler to reduce intake air temps.

For additional WRX forced induction research, IWSTI forums provide real-world build threads and troubleshooting advice.

Conclusion

Installing a 1.9L ProCharger on a Subaru WRX is a rewarding project that transforms the car’s character. The belt-driven power delivery provides instant, linear acceleration unlike the lag typical of turbocharged setups. By following the detailed steps above—paying close attention to bracket alignment, oil routing, and tuning—you can safely achieve the advertised 150+ horsepower gain. Remember that the key to long-term reliability lies in a professional dyno tune and diligent maintenance. With the right preparation and care, your WRX will deliver exhilarating performance for tens of thousands of miles.

For official documentation and kit updates, refer to the ProCharger website. Always cross-reference your specific vehicle year and engine code before purchasing or beginning work.