Overview of the Cobb Tuning Stage 2 Turbo Kit Upgrade

Upgrading your Subaru Forester with the Cobb Tuning Stage 2 Turbo Kit is one of the most effective ways to unlock significant horsepower and torque gains while maintaining daily-driver reliability. This kit is engineered specifically for turbocharged Subaru platforms, including the Forester XT models equipped with the EJ255 or FA20 turbo engines. Unlike generic universal kits, the Cobb Stage 2 kit integrates seamlessly with the factory ECU through the Cobb Accessport handheld tuner, providing a calibrated Stage 2 map that adjusts fuel, boost, and timing for optimal performance.

Before diving into the installation, understand that this upgrade is not a simple bolt-on affair. It requires mechanical aptitude, the correct tools, and a clean workspace. While this guide provides comprehensive instructions, always consult the official Cobb Tuning installation manual that ships with your kit for model-specific torque values and wiring diagrams. Additionally, joining a community like SubaruForester.org can provide real-world tips from owners who have performed this exact upgrade on their Foresters.

What You Will Need

Gather the following tools and components before starting. Missing a critical item midway through the job will lead to unnecessary downtime.

Components Included in the Kit

  • Cobb Tuning Stage 2 Turbo Kit (includes upgraded turbocharger, downpipe, intake, gaskets, and hardware)
  • Cobb Accessport V3 (required for ECU reflash; sold separately if not bundled)
  • Replacement oil feed line banjo bolts and copper washers (check if included)

Tool List

  • 3/8″ and 1/2″ socket sets (metric: 10mm, 12mm, 14mm, 17mm, 19mm, 22mm)
  • Torque wrench (0–150 ft-lbs range)
  • Combination wrenches (10mm–22mm)
  • Flathead and Phillips screwdrivers
  • Jack and two rated jack stands (minimum 3-ton capacity)
  • Safety glasses, mechanic’s gloves, and a fire extinguisher
  • Shop towels and brake cleaner
  • Drain pan and funnel
  • Engine oil (5W-30 synthetic, approved for turbo applications)
  • Coolant (Subaru Super Coolant or equivalent)
  • Thread locker (medium strength) and anti-seize compound

Preparation Steps

Proper preparation prevents costly mistakes. Follow these steps exactly:

  1. Disconnect the battery — remove the negative terminal first, then positive. Wait at least 10 minutes for the ECU capacitors to discharge.
  2. Park on level ground and chock the rear wheels. Lift the front of the Forester with a jack and place jack stands under the reinforced subframe points. Never rely on a jack alone.
  3. Drain engine oil — remove the oil drain plug and let the oil drain into a pan. Replace the crush washer and reinstall the plug loosely. You will need fresh oil for the new turbo’s break-in.
  4. Drain coolant — open the radiator drain petcock and remove the radiator cap to speed flow. Catch coolant for proper disposal.
  5. Remove the intercooler — on Forester XT models, the top-mount intercooler must come off to access the turbo. Label all hoses and bolts with painter’s tape.
  6. Prepare the new turbo — visually inspect the Cobb turbo for shipping damage. Rotate the compressor wheel by hand; it should spin freely without binding. Pre-oil the turbo bearing by pouring a small amount of fresh engine oil into the oil feed port and spinning the wheel again.

For reference, a detailed factory service manual for your specific Forester model year is invaluable. Subaru’s official owner support site provides downloadable manuals for most years.

Removing the Stock Turbocharger

With your Forester prepped, proceed to remove the factory turbo. Work methodically to avoid stripping fasteners or damaging adjacent components.

Disconnect Air and Exhaust Systems

  • Unclamp the intake duct from the turbo inlet and remove the air filter box assembly completely.
  • Loosen the four bolts securing the exhaust downpipe to the turbo. The upper two bolts are often accessed from above; the lower two require crawling underneath. Apply penetrating oil if the nuts are corroded.
  • Disconnect the oxygen sensor wiring harness from the downpipe. Note: the front O2 sensor is delicate; use an O2 sensor socket to avoid rounding the hex.
  • Remove the downpipe entirely. Set it aside; you will not reuse it with the Stage 2 kit.

Detach Oil and Water Lines

  • Locate the oil feed line attached to the top of the turbo. Unbolt the banjo fitting, capturing the two copper washers on each side. Replace these washers during reassembly — do not reuse old ones.
  • Loosen the oil return line (large banjo at the bottom of the turbo). Expect some residual oil to drip.
  • Disconnect the coolant lines: one feed and one return. Use pliers to release spring clamps; tube the ends to minimize spillage.

Unbolt the Turbo from the Engine

  • Remove the four nuts securing the turbo to the exhaust manifold (typically 14mm). If the studs spin out with the nut, use a stud extractor or double-nut method to back them out gently.
  • Carefully lift the stock turbo out of the engine bay. Rotate it to clear the coolant hard lines and engine block. Place it on a clean surface.
  • Clean the mounting surface on the exhaust manifold using a gasket scraper and brake cleaner. Remove any old gasket material.

Inspect the removed turbo for play in the shaft. Excessive axial or radial play may indicate the need to flush your oil system before installing the new unit.

Installing the Cobb Tuning Stage 2 Turbo Kit

The installation of the Cobb turbo follows the reverse of removal, but with critical differences in torque specifications and component alignment.

Mount the New Turbo

  • Apply a thin layer of anti-seize to the exhaust manifold studs (not to the nuts — use anti-seize on the studs only to prevent galling).
  • Place the new OEM-style turbo gasket (supplied with the kit) onto the studs.
  • Lower the Cobb turbo into position. Ensure the oil return port faces downward and the coolant ports align with your lines.
  • Thread the four nuts onto the studs. Torque them to the manufacturer specification: typically 30–35 ft-lbs for EJ engines. Check the supplied instructions — do not overtorque.

Connect Oil and Coolant Lines

  • Install new copper washers on the oil feed banjo bolt. Torque the banjo bolt to 15–20 ft-lbs (tight, but not so tight that you crush the washers unevenly).
  • Reconnect the oil return line using a new gasket. Torque to 12–15 ft-lbs.
  • Attach the coolant lines. If you replaced the spring clamps with screw-type clamps, do not overtighten — they can cut the rubber hose wall.

Install the Downpipe (Included in Kit)

  • The Cobb Stage 2 downpipe is typically a high-flow, catted or catless design. Apply anti-seize to the downpipe flange bolts.
  • Thread the two upper bolts first, then the two lower. Torque all four to 35–40 ft-lbs in a cross pattern.
  • Reconnect the oxygen sensor(s). The Stage 2 kit may require extending the rear O2 sensor wire; use the included extension harness.

Install the Intake System

  • The Cobb intake replaces the restrictive factory airbox and MAF housing. Mount the filter securely to the MAF sensor housing, ensuring the sensor element is oriented correctly (typically toward the filter).
  • Use the supplied silicone couplers and T-bolt clamps. Do not overtighten — strip the threads on the clamp if you go past hand-tight plus a quarter turn.
  • Reconnect the PCV and breather hoses as shown in the Cobb diagram.

For detailed downpipe installation for the Forester XT, refer to this Cobb Tuning installation library.

Tuning with the Cobb Accessport

After the mechanical installation, your Forester must be tuned. The Cobb Stage 2 kit is designed to work with the Accessport's pre-loaded Stage 2 map for your specific Forester model.

  • Reconnect the battery. Cycle the key to the ON position without starting the engine.
  • Plug the Accessport into the OBD-II port under the dashboard.
  • Select “Install Tune” and choose “Stage 2 93 Octane” (or your appropriate fuel grade). Follow the on-screen prompts. The process takes about 15 minutes.
  • Once flashed, the ECU will reset. Turn the ignition OFF for 10 seconds, then start the engine.

Important: Do NOT drive the vehicle hard until the ECU has completed idle and partial-throttle learning — allow about 10 minutes of gentle driving. Monitor the Accessport for knock correction, boost pressure, and fueling trims. If you see consistent negative knock correction values (e.g., -3° or greater), stop driving and consult Cobb’s support or a professional dyno tuner.

Post-Installation Checks and Break-In

After the first start, perform these checks:

  • Check for leaks — inspect all oil, coolant, and air connections while the engine idles. Use a flashlights; any trace of oil mist indicates a loose banjo or gasket.
  • Verify boost pressure — with the Accessport, watch the boost gauge during a gentle test drive. The Stage 2 map targets approximately 18–20 psi on the Forester XT. If boost exceeds 22 psi, reduce throttle immediately.
  • Listen for unusual noises — a high-pitched whine from the turbo is normal during spool; grinding, scraping, or rattling means mechanical contact.
  • Check fluid levels — top off coolant and engine oil. Run the engine to operating temperature, then recheck.
  • Perform the first oil change after 500 miles — the new turbo will seat and small metal particles may flush into the oil. Use high-quality synthetic 5W-30 and a new filter.

Maintenance Tips for Longevity

  • Use high-quality synthetic oil and change every 3,000–4,000 miles. The Stage 2 turbo spins faster than stock and generates more heat.
  • Let the turbo cool down before shutting off the engine after hard driving. Idle for 30–60 seconds to allow the oil to carry heat away from the bearings.
  • Inspect the intake filter regularly. The oiled cotton element in the Cobb intake should be cleaned and re-oiled every 15,000 miles.
  • Upgrade the intercooler (top-mount or front-mount) if you plan further modifications. The stock top-mount can heat-soak quickly at Stage 2 power levels.

Conclusion

Installing the Cobb Tuning Stage 2 Turbo Kit on your Subaru Forester is a transformative upgrade that delivers sharp throttle response and meaningful horsepower gains — typically 80–100 whp over stock on a modern Forester XT. By following this expanded guide, paying careful attention to torque specs, and utilizing the Cobb Accessport for proper calibration, you can complete the installation with confidence. Always prioritize safety, use factory-specified fluids, and never skip the tuning step. For ongoing support, the Cobb community and dedicated Subaru forums are excellent resources. Enjoy the enhanced driving experience of your Forester with its new Stage 2 power.