Introduction: Why a ProCharger Centrifugal Supercharger for Your WRX?

For Subaru WRX owners seeking a significant and reliable power increase, a centrifugal supercharger offers distinct advantages over turbochargers. Unlike traditional turbo systems that rely on exhaust gas flow and can introduce lag, a supercharger is belt-driven, providing immediate boost response and linear power delivery. The 1.8L ProCharger kit is specifically engineered for the WRX’s compact engine bay, delivering substantial horsepower gains—often 80–120 hp at the wheels depending on supporting modifications—without the heat soak and complex plumbing of a turbo swap. This guide provides a step-by-step process for a successful installation, covering everything from tool preparation to final tuning. Whether you’re a seasoned DIY mechanic or tackling a forced induction build for the first time, following these instructions carefully will help you achieve a safe, high-performance result.

Tools and Materials Required

Before beginning, verify that you have all components from the 1.8L ProCharger centrifugal supercharger kit (part number varies by WRX model year). In addition to the kit, you’ll need the following tools and consumables:

  • Socket set (metric: 8mm, 10mm, 12mm, 14mm, 17mm, 19mm)
  • Combination wrenches (same sizes as sockets)
  • Torque wrench (ft-lb and in-lb capability)
  • Ratchet, extensions, and universal joint
  • Drill and drill bits (for bracket mounting if needed)
  • Gasket maker (high-temp RTV silicone)
  • Coolant (Subaru Super Blue or equivalent ethylene glycol mix)
  • Engine oil (5W-30 or recommended weight for your climate)
  • Vacuum line (3/16″ and 1/4″ silicone)
  • Fuel line (5/16″ high-pressure EFI rated)
  • Safety glasses and gloves
  • Jack and jack stands (for wheel removal if accessing under-engine brackets)
  • Shop manual or wiring diagram (for your specific WRX year)

Optional but recommended: a boost gauge and a wideband air/fuel ratio monitor to verify operation during test drives.

Preparation Steps

1. Disconnect the Battery

Disconnect the negative terminal of the battery using a 10mm wrench. Isolate the cable end with a rag or zip tie to prevent accidental contact. This eliminates the risk of electrical shorts while working near the alternator, sensors, and engine ground straps.

2. Remove Engine Cover and Sound Deadening

Unscrew the plastic engine cover (typically held by two or three 10mm bolts or push-clips). On many WRX models, there is also a sound-deadening pad beneath the cover—remove it gently to avoid tearing. Set these aside in a clean area.

3. Drain Coolant and Engine Oil (If Required by Kit)

ProCharger’s installation instructions may call for draining the engine coolant to access the water pump belt routing for the supercharger drive system. Place a drain pan under the radiator petcock and open it. Similarly, you might need to drain engine oil if the kit includes an oil feed line for the supercharger gearcase. If so, remove the oil drain plug and replace the crush washer before reinstalling.

Tip: Use a new OEM Subaru oil filter during the post-installation oil change to ensure proper flow and filtration.

4. Remove the Intake and Windshield Washer Reservoir

The stock intake snorkel and airbox must be removed to make room for the supercharger. Unbolt the airbox, disconnect the mass airflow (MAF) sensor, and remove the entire intake tract. On many WRX chassis, the windshield washer reservoir will also require relocation to accommodate the supercharger piping. ProCharger typically includes a relocation bracket—follow the included instructions for bolting it to the inner fender area.

Installing the Supercharger System

With the engine bay prepared, proceed step by step. Reference the ProCharger manual specific to your kit as wire routing and bracket locations differ slightly between 2002–2007 (GD) and 2008–2014 (GR/GV) WRX models. All torque values given are typical; confirm with your kit’s spec sheet.

5. Install the Supercharger Mounting Bracket

Locate the steel mounting bracket that bolts to the driver’s side of the engine block (near the alternator). Clean the mounting surface with brake cleaner. Apply a thin film of thread locker (blue Loctite) to the supplied bolts. Torque the bracket bolts to 45 ft-lb (61 Nm) in a cross pattern. Do not overtighten as the bracket is cast and can crack.

6. Mount the Supercharger Head Unit

Lift the ProCharger head unit onto the bracket. Align the four mounting holes with the bracket slots. Hand-tighten the nuts to 20 ft-lb initially, then torque to 40 ft-lb (54 Nm) after verifying belt alignment. The supercharger pulley should be perfectly parallel to the crankshaft pulley. Use a straightedge across both pulley faces to check alignment. If misaligned, loosen and adjust with thin washers on the bracket bolts.

7. Install the Intercooler and Charge Piping

Most ProCharger kits for the WRX include an air-to-air intercooler that mounts in the lower front bumper opening. You may need to remove the plastic lower grille and drill a few holes for the intercooler brackets. Secure the intercooler using the supplied stainless hardware—tight to hand pressure plus 1/4 turn; do not deform the plastic core supports.

Connect the charge pipe from the supercharger outlet to the intercooler inlet. This is often a 2.5″ to 3″ aluminum or silicone hose. Use T-bolt clamps at every connection. Important: Apply a light coat of silicone lubricant to the hose ends to prevent tearing. Ensure the pipe does not rub against the hood or suspension components—reroute if necessary using provided couplers.

8. Connect the Intake Piping and Air Filter

Attach the intake pipe (with MAF sensor mount) to the supercharger intake bell. The filter should be positioned in a cool, dry location behind the headlight or lower grille. Use a dry-media air filter if possible to avoid contaminating the MAF sensor with oil. Secure the intake pipe with the supplied bracket to prevent vibration.

9. Install the Belt Drive System

Replace the engine’s accessory belt with the longer serpentine belt included in the kit. The routing will typically go: crankshaft pulley → alternator → supercharger pulley → idler pulley → water pump → tensioner. Use the belt routing diagram from ProCharger. Set the belt tensioner to the marked position; after a few minutes of engine run time, recheck tension—it should deflect about 1/2″ at the longest span when pressed firmly.

10. Fuel System Modifications

Critical for safe operation: Centrifugal superchargers increase manifold pressure, requiring additional fuel to avoid lean conditions. The ProCharger kit often includes a fuel pressure regulator upgrade or larger injectors. If using the supplied injectors (e.g., 550 cc/min for Stage 1), remove the stock injectors, replace the O-rings, and install the new ones. For higher boost levels, consider an in-tank fuel pump upgrade (such as a Walbro 255 lph). Connect the fuel return line to the new regulator if the kit requires a return-style system. Leak-test the fuel system by pressurizing it to 45 psi using a hand pump; inspect all connections.

11. Vacuum Line Routing and Bypass Valve

Install the supplied blow-off/bypass valve on the charge pipe between the supercharger and throttle body. Connect a 5/32″ vacuum line from the bypass valve port to a manifold vacuum source (e.g., the intake manifold port near the throttle body). Use a T-fitting if needed for the boost gauge. Route vacuum lines away from hot surfaces and moving parts.

12. Reconnect Cooling and Electrical Systems

Refill the cooling system with the drained coolant or fresh Subaru coolant mixed 50/50. Bleed air from the system by idling the engine with the radiator cap off and adding coolant until the thermostat opens. Reconnect all previously disconnected electrical connectors, including MAF sensor, IAT sensor (if relocated), and boost control solenoid (if using an electronic boost controller).

Final Steps and First Startup

13. Reconnect the Battery and Check Fluid Levels

Reattach the negative battery terminal. Verify engine oil is at the full mark on the dipstick. Top up power steering fluid and brake fluid. Inspect all clamps, hoses, and wiring one final time.

14. Prime the Supercharger Gearcase (If Applicable)

Some ProCharger head units require a pre-oiling step: remove the oil fill plug on top of the gearcase and add approximately 60 mL of the supplied synthetic gear oil. Rotate the supercharger pulley by hand a few times to distribute the oil. Reinstall the plug.

15. Start the Engine and Check for Leaks

Start the engine and let it idle. Immediately listen for any metallic rubbing, belt squeal, or air hissing. Check all hose connections for coolant or fuel leaks. Let the engine reach operating temperature (about 5 minutes of idle). Monitor the boost gauge—it should read vacuum at idle (around 18–22 inHg). Rev the engine gently to 2000–3000 rpm and observe that boost rises slightly (2–3 psi) but does not spike.

16. Test Drive and Data Logging

Take the vehicle for a test drive on a quiet road. Accelerate gently for the first few miles to allow the gearcase oil to circulate. Then perform a few 3rd-gear pulls from 2500 rpm to 5500 rpm while monitoring boost, air/fuel ratio (AFR), and engine knock (if using a tunable ECU). Target AFR at wide-open throttle should be around 11.5–12.0:1. If AFR leans out or knock occurs, reduce throttle and have the vehicle professionally tuned immediately.

Tuning and Supporting Modifications

Installing a ProCharger without proper engine management is dangerous. The kit typically includes a fuel controller or requires an aftermarket ECU reflash. For maximum power and reliability, consider:

  • ECU reflash or standalone (e.g., Cobb Accessport or EcuTek)
  • Upgraded intercooler for sustained boost on track days
  • 3-inch exhaust system to reduce backpressure
  • Oil cooler to manage increased oil temperatures

Consult a reputable Subaru tuner for a custom calibration. Resources: ProCharger official site for technical bulletins, IWSTI forums for real-world install tips, and Cobb Tuning for calibration products.

Conclusion

A 1.8L ProCharger centrifugal supercharger transforms the driving experience of a Subaru WRX by providing instantaneous, linear power. While the installation is involved—requiring mechanical confidence, proper tools, and attention to detail—the result is a well-integrated forced induction system that retains daily-driver refinement. By following this expanded guide, you minimize the risk of installation issues and ensure that the supercharger performs as engineered. Always prioritize safety: verify all connections, use quality fluids, and invest in professional tuning. Your WRX, now with forced induction, will reward you with exhilarating acceleration for years to come.