Understanding the AMS Performance Stage 2 Kit for the 2G Eclipse

The Mitsubishi Eclipse GSX and GST (2G, 1995-1999) remain icons in the turbocharged import community. For owners looking to move beyond basic bolt-ons, the AMS Performance Stage 2 Kit has long been a benchmark upgrade. AMS (Automotive Motorsports) in Chicago built its reputation engineering reliable, high-horsepower DSM systems. This kit is engineered as a complete package, not a collection of mismatched parts. It includes:

  • Garrett GT3076R turbocharger with a custom AMS manifold and wastegate actuator
  • MagnaFlow stainless steel downpipe and exhaust (2.5″ or 3″ options)
  • AMS front-mount intercooler kit (bar-and-plate core, polished piping)
  • Precision 1,000cc or 1,200cc fuel injectors (matched for high ethanol content if desired)
  • Walbro 450 lph fuel pump with rewire kit
  • Blow-off valve (HKS or Tial, depending on kit iteration)
  • K&N air filter with intake piping

Everything is designed to work together without excessive custom fabrication. The kit targets a proven 400–450 wheel horsepower on pump gas and up to 500+ whp on race fuel or E85 with proper tuning. This is a substantial step up from the stock 210 hp (GST) or 190 hp (GSX).

For reference, the original AMS Stage 1 kit typically adds an upgraded sidemount intercooler, fuel pump, and boost controller for ~350 whp. Stage 2 moves to a genuine Garrett center-section turbo and full exhaust. You can view current product details on the AMS Performance official site.

Preparation: Tools, Space, and Supporting Mods

Before unbolting anything, gather the right tools and make sure your car is ready. The 2G engine bay is tight, and a clean, well-lit workspace will save hours of frustration.

Essential Tools

  • Metric socket set (8mm to 19mm), including deep wells
  • Combination wrenches (10, 12, 14, 17, 19 mm)
  • Torque wrench (ft-lb and in-lb ranges)
  • Pick set and small pry bars for stubborn connectors
  • Jack stands and floor jack
  • Creeper or kneepads
  • Coolant catch pan and drain pan
  • PB Blaster or equivalent penetrating oil
  • Safety glasses and nitrile gloves

Supporting Mods to Prepare

The Stage 2 kit will overwhelm a stock drivetrain and fueling system. AMS assumes you already have a boost controller (manual or electronic), a wideband oxygen sensor and gauge, and an engine management solution such as ECMLink V3, AEM EMS, or a standalone FlashPro-like device. If you haven’t tuned yet, plan for a dyno session immediately after installation – more on that in the post-installation section.

Also consider upgrading your clutch. The 2G’s stock clutch begins slipping around 300 whp. A South Bend Stage 3 or ACT 2600 kit is highly recommended. Check forums like DSM Tuners for long-running threads on kit compatibility.

Step-by-Step Installation Guide

We’ll break down the physical installation into logical stages. Expect a full weekend if this is your first time; a veteran DSM mechanic can do it in eight to ten hours. Always refer to the official AMS instructions shipped with your kit, as revisions occur.

1. Disconnect Battery and Drain Fluids

Always disconnect the negative battery terminal first. Drain the engine coolant completely (the intercooler piping requires the lower radiator hose removal). You may also want to drain the engine oil to avoid spills when removing the turbo oil return line.

2. Remove Stock Intake, Turbo, and Intercooler

Start by pulling the intake pipe from the air filter box. The stock 2G turbo (T25 on GST, 14B on GSX) is removed from underneath. You’ll need to unbolt the O2 housing, downpipe, oil feed line, and water lines. Keep a shop towel handy for residual oil. The stock sidemount intercooler comes out from behind the passenger side bumper – you may need to remove the bumper cover for access. This is also a good time to inspect the radiator and cooling fans; consider upgrading to a slim fan if clearance is tight.

Note: Stock turbo bolts are notorious for seizing. Spray them with penetrating oil the night before. If a bolt snaps, extract it with a quality screw extractor or drill set.

3. Install the Upgraded Turbocharger and Manifold

The AMS kit includes a tubular stainless steel exhaust manifold. It must be torqued to the cylinder head in a crisscross pattern at 35-40 ft-lb. Install the turbo onto the manifold with a new gasket. The Garrett GT3076R has a .63 A/R turbine housing – this size spools quickly on a 2.0L 4G63. Tighten the turbo-to-manifold bolts to 30-35 ft-lb. Attach the oil feed line (restrictor may be needed for journal bearing turbos – confirm with AMS). Use a copper washer on the oil return line gasket.

4. Mount the Front-Mount Intercooler

The AMS intercooler is a bar-and-plate core designed for a direct fit behind the GSX/GST front bumper. Remove the lower bumper support bracket; the intercooler mounts using brackets and bolts supplied in the kit. Route the polished piping from turbo to intercooler and to the throttle body. You may need to trim the lower radiator fan shroud slightly. Use T-bolt clamps on all silicone couplers – they prevent boost leaks better than worm-gear clamps. Torque clamps evenly to avoid distorting the piping.

5. Replace Fuel Injectors and Fuel Pump

Access the injectors by removing the fuel rail (two bolts) and unclipping the stock injectors. The AMS kit’s Precision injectors are clip-on direct replacements. Before seating them, lubricate the o-rings with engine oil. Reinstall the fuel rail, torquing the bolts to 10 ft-lb – do not overtighten. For the fuel pump, drop the rear seat cushion, remove the access plate, and lift the module. Replace the stock pump with the Walbro 450 lph, ensuring the rubber isolator sleeve is intact. Reuse the stock pickup sock if it’s clean; otherwise use the included filter. This pump is noisy at idle but normal.

6. Install the Exhaust System

The AMS downpipe is 3″ mandrel-bent stainless steel and will bolt directly to the new turbo’s O2 housing. Use a new gasket. Then connect the cat-back (or full exhaust) section. The MagnaFlow muffler provides a deep tone with minimal drone. Torque all flange bolts to 25-30 ft-lb. Protect the oxygen sensor bungs – you’ll be moving the wideband sensor here later.

7. Reassemble Intake, BOV, and Vacuum Lines

Install the alloy intake pipe and K&N filter. The blow-off valve (BOV) should be mounted in the cold-side piping. If your BOV is not recirculated, you must tune the ECU to avoid rich stalling between shifts. For street driving, recirculate it back into the intake using a recirculation fitting. Check all vacuum lines: replace them with silicone if aged. The boost source for the wastegate should come directly from the compressor housing, not a manifold port, to reduce boost spikes.

Post-Installation Checks and Tuning

With everything bolted together, the real work begins. Never start the car without verifying the following:

  • All bolts and clamps are tight, especially turbo and intercooler couplers
  • Oil level is correct and fresh 5W-40 synthetic or 10W-40 break-in oil is used
  • Coolant is filled and bled – the 4G63 can trap air; run the car with the radiator cap off until the thermostat opens
  • No loose wires near the exhaust manifold (protect with heat wrap if needed)
  • Wideband O2 sensor is installed and calibrated

Diagnostic and Tune

Using ECMLink V3 or AEM, load a base map from AMS or your tuner. Do not floor the throttle on the first start. Let the engine idle and warm to operating temperature. Check for smoke (blue = oil leak, white = coolant leak, black = rich tune). Perform a gentle test drive, watching boost levels. Your boost controller should be set to 20 psi for break-in. After 50-100 easy miles, return to the dyno for a full tune.

For those unfamiliar with tuning, consider visiting a shop that specializes in 4G63 engines. Websites like STM Tuned offer remote tuning services if you have a reliable logging setup. Another excellent resource is the ECMTuning wiki for base maps and tips.

What to Expect After Installation: Dyno Results and Driving Feel

Once properly tuned, your 2G Eclipse will feel like a different car. The GT3076R reaches full boost around 3,800 RPM on the 4G63, tapering to redline. Expect peak torque in the 4,200–5,500 RPM range. A well-tuned Stage 2 car on 93 octane typically makes 400–430 whp and 380–410 ft-lb of torque. On E85, numbers climb to 480–510 whp, depending on your turbo spec and fuel system headroom.

Drivability Changes

The car will require more throttle modulation to avoid overwhelming the tires in first and second gear – especially in a GSX with a good all-wheel-drive system. The exhaust note is louder but not obnoxious if you keep the included resonator. Expect the blow-off valve to be audible; many drivers enjoy the sound. Fuel economy will drop by 20-30% under hard driving, but cruising on the highway stays reasonable.

The Stage 2 kit also reveals weak points: motor mounts will need to be upgraded (Prothane or Innovative mounts) to reduce wheel hop. The transmission shifts will feel notchy – synthetic MT-90 fluid helps. Driveshaft and axles can handle 500 whp if your car is not abused with clutch dumps.

Common Pitfalls and Troubleshooting

  • Boost creep: If boost rises uncontrollably, the internal wastegate hole may need to be ported. AMS kits usually include an upgraded flapper to mitigate this, but check if you run an open downpipe.
  • Oil leaks from the turbo drain: Ensure the drain flange is perfectly aligned and the gasket is not pinched. Use a -10 AN return line if supplied.
  • Coolant air pockets: The 4G63 water pipe near the oil filter housing often traps air. Bleed using the small port on the thermostat housing.
  • Check engine light for large injectors: Without proper scaling in ECMLink, the ECU will throw codes for rich condition. Scaling for 1,000cc injectors is roughly half the stock latency; consult the injector data sheet.

Long-Term Maintenance and Upgrades

After installation, plan on oil changes every 3,000 miles with a high-quality synthetic oil (Mobil 1 or Liqui Moly). Spark plugs should be gapped to 0.028” and replaced every 10,000 miles – NGK BPR7ES or BPR8ES for higher boost. The fuel filter should be replaced at this interval too. If you track the car, consider a thermostatic oil cooler (AMS sells a kit) and a larger aluminum radiator.

The Stage 2 kit creates an excellent platform for future growth. Many owners later add a Garrett GT3582R, larger turbo manifold, or nitrous injection. But as-is, the Stage 2 package is a proven, daily-drivable setup that still wins at drag strips and autocross events.

Conclusion

Installing the AMS Performance Stage 2 Kit is the most comprehensive bolt-on upgrade you can make to a 2G Eclipse without stepping into full engine build territory. The kit is well-engineered, with top-tier components that work together. Success demands careful attention to installation details, supporting mods, and professional tuning. The result is a 400+ whp turbocharged machine that can still run errands and commute – as long as you respect the throttle. Whether you’re chasing 12-second quarter-miles or just want a thrill on back roads, the AMS Stage 2 delivers.