The MAPerformance Stage 2 Turbo Kit is one of the most popular power-adders for Subaru WRX and STI enthusiasts looking to move beyond basic bolt-ons. While a Stage 1 tune and cat-back exhaust can wake up an EJ or FA engine, Stage 2 turbo systems deliver a dramatic jump in both peak horsepower and usable torque. This article provides a complete breakdown of what to expect during installation, what tools and skills are required, and the realistic performance numbers you can achieve after proper tuning. Whether you are a seasoned DIY installer or planning to hand the project to a professional shop, understanding every stage of the process ensures you maximize reliability and horsepower.

Overview of the MAPerformance Stage 2 Turbo Kit

The MAPerformance Stage 2 Turbo Kit is engineered for drivers who want a substantial increase in power without moving to a built block or a massive GT-series turbo. It bridges the gap between a simple downpipe-and-tune upgrade and a full rotated-mount system. The kit is available for 2008–2014 WRX/STI (GR chassis) and 2015–2021 WRX/STI (VA chassis) models, with slight variations in oil line routing and intercooler fitment.

Key components included in the kit:

  • Turbocharger – A billet wheel, journal-bearing or ball-bearing upgrade (typically a Garrett or BorgWarner core) designed to flow more air than the stock IHI or Mitsubishi unit. The MAPerformance unit often features a 10.5cm or 11.5cm turbine housing for quicker spool while still supporting over 400 whp.
  • Wastegate – An integral or external wastegate (depending on kit revision) with a 15–18 psi spring for precise boost control. External gate versions reduce boost creep often seen with high-flow downpipes.
  • Fuel injectors – Matched 1000cc or 1300cc fuel injectors (depending on year) to support the increased airflow. These are plug-and-play with the stock harness.
  • High-flow intercooler – A bar-and-plate core that is larger and more efficient than the factory top-mount. Some kits include a front-mount intercooler (FMIC) with cast aluminum piping, while others keep a TMIC design for simpler installation.
  • Downpipe – A catted or catless downpipe with 3-inch diameter, designed to mate with the turbo outlet and your existing exhaust. A high-flow catalytic converter option is available for emissions compliance.
  • Oil lines and coolant lines – Braided stainless steel lines with AN fittings for reliable oil supply and return to the turbo. The kit includes all necessary gaskets and crush washers.
  • Heat shielding – A turbo blanket or heat shield to reduce under-hood temperatures and protect nearby components.

The kit is designed to work with the stock intake system, though MAPerformance recommends replacing the intake with a cold-air or short-ram unit for maximum gains. For complete details on the exact components for your specific model, refer to the official MAPerformance turbo kit collection.

What to Expect During Installation

Installing a Stage 2 turbo kit is not a weekend project for a novice. You should have a solid working knowledge of turbocharged engine systems, including fuel delivery, intercooling, and boost control. Plan on a full two-day install for a first-timer; experienced mechanics can complete the job in 8–10 hours.

Tools and Workspace Requirements

Gather these tools before starting. Missing a single socket can add hours to the job.

  • Metric socket set (8mm to 19mm, including deep sockets)
  • Combination wrenches (10mm, 12mm, 14mm, 17mm, 19mm)
  • Torque wrenches (1/2” drive for lug nuts and components, 3/8” drive for smaller bolts)
  • Screwdrivers (flathead and Phillips), trim removal tools
  • Jack and four jack stands (or a lift)
  • Drain pan for coolant and oil
  • Aspirator or vacuum tool for coolant removal
  • Fuel injector puller (if removing injectors from a side-feed rail)
  • Braided line wrench for AN fittings
  • Safety glasses, gloves, and fire extinguisher (mandatory)

Also prepare new engine oil, coolant (Subaru Super Blue or equivalent), and a bottle of brake cleaner for cleaning mounting surfaces. If you plan to upgrade the fuel pump, buy a DW300 or AEM 340 lph pump—it’s smart to do it at the same time.

Pre-Installation Steps

Before you remove a single bolt, ensure you have a reputable tuning solution. A COBB Accessport or open-source tune (e.g., EcuTek) is mandatory. The MAPerformance Stage 2 kit will not run safely on stock mapping; boost pressure and fueling must be calibrated by a professional tuner. If you do not have a tuner lined up, work with a shop like Tuning Alliance or P-Tuning who can provide an e-tune or dyno tune.

Disconnect the battery negative terminal. Drain the engine oil and coolant (remove the radiator cap and open drain cock). Remove the intercooler, intake ducting, and downpipe to access the stock turbo. Label all vacuum lines and electrical connectors with tape—this will save you agony during reassembly.

Removing the Stock Turbo

Difficulty: moderate. The stock turbo is located under the intake manifold and is attached to the exhaust manifold flange with four 14mm nuts. Use penetrating oil (e.g., PB Blaster) on the nuts the night before to avoid snapping studs.

  • Disconnect the oil feed line from the top of the turbo (6mm Allen key on some models, or a flare nut wrench).
  • Remove the oil return line from the bottom (two 10mm bolts). Be ready for residual oil to drip.
  • Unbolt the turbo support bracket (12mm bolt on the transmission housing).
  • Remove the four exhaust manifold nuts using a swivel socket for the lower two.
  • Lift the turbo upward and out. On some 2015+ STI models, you may need to temporarily remove the alternator bracket for clearance.

Inspect the banjo bolts and crush washers on the oil feed line; replace any that are deformed. It’s wise to replace the oil feed line itself with the new braided line from the kit—the stock lines are notorious for clogging.

Installing the New Turbocharger and Components

Begin by installing the new intercooler. If you have a front-mount kit, mount the core before you put the turbo in place. For a top-mount, drop the new unit onto the intake manifold after the turbo is in.

  • Fuel injectors: Remove the fuel rails (two 12mm bolts per rail), pop out the stock injectors, and install the new 1000cc units. Apply a light coat of fuel-friendly grease to the O-rings. Seat them firmly, reinstall the rails, and torque the bolts to 19 lb-ft.
  • Turbo oil/coolant lines: Attach the braided lines to the new turbo while it’s still out of the car. Use thread sealant on the oil feed side (not PTFE tape—use a liquid or paste sealant rated for high temp).
  • Mount the turbo: Position the new turbo onto the exhaust manifold studs. The gasket should be new. Torque the four nuts to 35 lb-ft.
  • Downpipe: Attach to the turbo outlet with two gaskets (one turbo-to-downpipe, one downpipe-to-catback). Use anti-seize on the bolts. Do not tighten fully until the downpipe is aligned with the cat-back exhaust flange.
  • Intake and boost control: If your kit includes a blow-off valve, install it now. Run new vacuum lines from the turbo compressor nipple to the wastegate and boost control solenoid (if retaining the stock BCS). The MAPerformance kit includes a diagram; follow it exactly.

For a detailed walkthrough, the MAPerformance install guide provides year-specific torque specs and photos. Do not rely solely on this article—always verify against the official guide.

Reassembly and Fluid Checks

Reconnect everything: intercooler, charge pipes, intake, battery, and all connectors. Prime the oil system by cranking the engine (with fuel pump fuse removed) for 10–15 seconds. Then install the fuel pump fuse, start the engine, and look for leaks. Check the oil level immediately after the first startup—the turbo will absorb some oil. Add coolant and bleed the system using the upper radiator bleeder screw.

Let the engine idle for at least 3 minutes. Listen for any unusual noises, especially a whistling turbo (normal) versus a grinding sound (bad). If all is quiet, take a short test drive staying out of boost. After 10 miles of low-load driving, do a single moderate pull (up to 10 psi) and log with the Accessport to check for knock or fuel trims.

Performance Numbers: Realistic Gains

The MAPerformance Stage 2 Turbo Kit is capable of producing between 350 and 420 wheel horsepower on 93 octane pump gas, depending on the specific turbo wheel, engine condition, and altitude. On E85, numbers can climb to 420–460 whp. Torque peaks are equally impressive: 380–440 lb-ft on pump gas, 440–480 lb-ft on ethanol.

Breakdown by Fuel Type and Tune

  • 93 octane (pump gas): 350–380 whp, 370–410 lb-ft. Boost around 20–23 PSI. A conservative, reliable tune will keep peak torque below 400 lb-ft to avoid rattling the ringlands.
  • E85 (flex fuel or dedicated): 400–460 whp, 430–480 lb-ft. Ethanol’s higher octane allows more ignition advance and up to 25–26 PSI boost. Fuel system upgrades (larger pump and lines) are required.
  • 93 octane + meth injection: Falls between pump and E85, around 380–420 whp with extra margin against detonation.

These numbers come from real dyno sheets posted on NASIOC and Subaru forums. One common dyno used is a Mustang Dyno (reads lower than a Dynojet). On a Dynojet, expect 15–20 whp higher. The important metric is usable power under the curve: the Stage 2 turbo will spool to positive boost by 2800 rpm and hit full boost around 3700 rpm, reducing lag compared to larger turbos.

Comparison to Stage 1 and Stock

ConfigurationWHP (93 octane)WTQ (93 octane)
Stock WRX/STI240–270240–280
Stage 1 (tune only)280–310300–340
Stage 2 (MAPerformance kit)350–380370–410

Those gains aren’t just peak numbers—area under the curve improves dramatically. The Stage 2 kit can deliver 50 lb-ft more torque at 3500 rpm than a Stage 1 tune, making daily driving much more responsive.

Maintenance and Reliability Considerations

Any turbo upgrade places additional stress on engine internals. Subaru EJ engines have notoriously weak pistons (especially the 2.5 L). To ensure reliability, follow these guidelines:

  • Oil change interval: Reduce to every 3,000 miles (5,000 km). Use a high-quality 5W-40 synthetic (e.g., Motul 300V or Pennzoil Ultra Platinum).
  • Heat management: Install a turbo blanket and wrap the downpipe to prevent heat soak to the firewall and hydraulic clutch line.
  • Fuel system: If you plan to push toward 400 whp, upgrade to a fuel pressure regulator and return line. The stock pressure regulator can become a restriction at high flow rates.
  • Intercooler upgrades: If using the included top-mount, consider a water-methanol injection kit for hot summer track days. An FMIC is better for road course use but adds more piping to check for leaks.
  • Clutch: Any Stage 2 setup will exceed the stock clutch’s torque capacity after a few thousand miles. Plan on upgrading to a Stage 2 or Stage 3 clutch kit (e.g., ACT or Exedy).

Monitor boost, AFR, and knock correction with your Accessport on every drive. If you see negative knock correction values beyond -2.8, back off immediately and check for issues. A lightweight flywheel is not recommended for daily drivers—the added vibration can accelerate bearing wear.

Tuning: The Most Critical Step

The MAPerformance Stage 2 kit will not run safely without a custom tune. Even if a base map is included with the kit, it is a conservative starting map, not a finalized tune. You must work with a reputable tuner who can adjust fuel tables, boost targets, and ignition timing to match your specific fuel quality, altitude, and driving conditions.

Two tuning options are common:

  • E-tune: You send data logs to a tuner via email or remote session. This is convenient and cheaper but requires you to perform pulls on public roads safely. Expect 5–7 revisions to dial in the tune. Prices range $300–$500.
  • Dyno tune: Your car is strapped to a load-bearing dyno, and the tuner makes real-time adjustments. This is the safest and most power-optimizing approach. Expect 2–4 hours on the dyno. Prices range $500–$900.

A good tuner will also calibrate the boost control solenoid to avoid boost spikes. Many Stage 2 setups have a habit of over-boosting to 24–26 PSI if not properly tuned—this can crack ringlands instantly. Always request a torque-limited tune for the lower gears to protect the transmission and driveline.

Conclusion

The MAPerformance Stage 2 Turbo Kit offers a proven path to over 400 wheel horsepower on these modern Subaru platforms, transforming the car from a modest sport compact into a genuine street predator. The installation is involved and requires mechanical competence, but the reward is a broad, powerful torque curve that pulls from 3000 rpm all the way to redline. With realistic performance numbers of 350–420 whp on pump gas and up to 460 whp on E85, this kit competes favorably with much more expensive rotated turbo setups while retaining a near-stock feel for daily driving.

The key to success is preparation: gather all tools, follow the manufacturer’s instructions, and invest in a professional tune. Do not cut corners on the fuel system or oiling circuit. When installed correctly and tuned wisely, the MAPerformance Stage 2 kit will give you years of reliable, exciting performance. For more real-world owner experiences, check out the IWSTI turbo forum where hundreds of users share their dyno sheets and installation tips.