Overview of the Forge Motorsport S3 IS38 Upgrade Kit

The Forge Motorsport S3 IS38 Upgrade Kit is engineered for the 2.0 TSI EA888 Gen3 engine found in the Audi S3, Volkswagen Golf R, and related MQB-platform vehicles. It replaces the factory IS20 turbocharger with the larger IS38 compressor wheel and turbine housing, sourced from the Audi RS3 and TTRS. Forge packages this turbo with an upgraded cast aluminum intercooler, CNC-machined charge pipes, silicone hoses, and all necessary gaskets and hardware. The result is a complete bolt-on system that increases airflow capacity without requiring extensive fabrication.

This kit is aimed at enthusiasts seeking a reliable 400+ wheel horsepower target on pump fuel with a proper tune. Unlike hybrid turbos or custom manifold setups, the IS38 upgrade maintains direct OEM compatibility, making it one of the most straightforward power-adders for the MQB platform. Forge’s version stands out by including a high-capacity intercooler that supports sustained boost pressure and reduces charge air temperatures, critical for consistent performance on track or during repeated pulls.

Understanding the IS38 Turbocharger

The factory IS20 turbocharger delivers strong low-end torque but runs out of steam above 5500 RPM. The IS38 uses a larger compressor wheel (11-blade vs 10-blade) and a larger turbine housing, shifting the power band higher while significantly increasing peak flow. On an otherwise stock engine, the IS38 can produce 330–360 whp with a Stage 2 tune. With supporting modifications like downpipe, intercooler, and ethanol fuel, output can exceed 420 whp.

Forge’s version of the IS38 includes a billet adjustable actuator that allows precise control over wastegate preload. This is a key improvement over the stock actuator, which often requires shimming to achieve the correct base pressure. The adjustable actuator simplifies setup and helps your tuner dial in boost response without mechanical modifications.

Performance Gains on the Dyno

Real-world dyno results from multiple independent shops show consistent gains:

  • Peak Horsepower: +80–120 hp on 93 octane with a Stage 2+ tune, Intake, downpipe, and intercooler. (Baseline 280 whp → 390–410 whp.)
  • Peak Torque: +70–100 lb-ft, with a flatter torque curve from 3500–6000 RPM.
  • Boost Threshold: Full boost arrives approximately 300–400 RPM later than IS20, but the trade-off is sustained pull to redline.

These numbers assume a proper ECU tune from a reputable calibrator such as EQT, Unitronic, 034Motorsport, or Integrated Engineering. Piggyback tuning is not recommended for the IS38 because it cannot adjust cam timing, direct injection timing, or turbo speed limits adequately.

Installation Tips for a Trouble-Free Upgrade

Installing the Forge IS38 kit is a medium-to-advanced job. Expect 6–10 hours of labor if you have experience with turbocharged VW/Audi engines. Below are detailed steps and common pitfalls.

Tools & Supplies

  • Metric socket set (10mm, 13mm, 15mm, 16mm, 18mm, 21mm)
  • Torque wrench (ft-lb and in-lb ranges)
  • E10, E12, and E14 Torx sockets (Triple Square equivalent for some bolts)
  • O2 sensor socket (22mm)
  • Pick set for removing clips
  • Jack, jack stands, or lift
  • Coolant, oil, and new crush washers
  • Anti-seize compound and thread locker (medium strength)
  • VCDS, OBDeleven, or ODIS for post-install adaptations

Step-by-Step Installation Process

1. Disconnect Battery and Drain Fluids
Remove the negative terminal. Drain coolant from the lower radiator hose and remove the oil filter to drain the oil. This prevents spills when disconnecting turbo oil lines.

2. Remove Engine Cover and Air Intake System
Remove the engine cover, intake hose, air filter box, and snorkel. Label all electrical connectors with tape.

3. Access and Remove the Factory IS20 Turbocharger

  • Disconnect the turbo outlet hose, charge air cooler hose, and the high-pressure fuel pump (if you have direct injection).
  • Unbolt the downpipe from the turbo and remove the O2 sensors.
  • Remove the turbo heat shield and the oil feed line (use a flare nut wrench to avoid rounding).
  • Unbolt the turbo from the exhaust manifold (8 bolts, torque 15 ft-lb). Remove the turbo away from the block, being careful not to drop debris into the oil return port.

4. Prepare the New IS38 Turbo
Transfer any necessary heat shields from the old turbo. Set the adjustable actuator to the recommended preload (typically 2–3 mm of rod travel from fully closed). Use a small air pump to verify the wastegate closes fully.

5. Install the Forge IS38 Turbo
Clean the exhaust manifold sealing surface. Use a new gasket (supplied) and apply a thin layer of copper spray gasket for extra sealing. Carefully position the turbo, finger-tighten all bolts, then torque to spec (15 ft-lb for manifold bolts, 7 ft-lb for oil line banjo bolt).

6. Install the Upgraded Intercooler
Remove the front bumper or the lower grille to access the stock intercooler. The Forge unit is a direct-fit bar-and-plate design. Reuse the OEM mounting brackets. Ensure all O-rings are lubricated with silicone paste. Torque the charge pipe connections to 7 ft-lb to avoid cracking the plastic end tanks (if using aftermarket charge pipes).

7. Reconnect Everything

  • Reinstall the downpipe with a new gasket (torque 28 ft-lb).
  • Reconnect coolant and oil lines. Fill with approved G12+ coolant and 5W-40 synthetic oil.
  • Reconnect the battery.

8. Perform Leak Checks and Adaptation
Before starting, pressurize the charge air system with a boost leak tester (20 psi) to check for leaks at all connections. Use VCDS or OBDeleven to prime the turbo oil feed (watch priming procedure). Then start the engine and let it idle for 2 minutes. Check for oil or coolant leaks.

Post-Installation Checks & Break-In

  • Verify that the wastegate actuator arm does not contact the engine block or downpipe.
  • Check boost pressure under part throttle; it should build smoothly to target (typically 26–29 psi on a high-boost tune).
  • Log air-fuel ratio and boost with a laptop tool; ensure no boost oscillation.
  • Drive gently for the first 100 miles to allow the turbo seals to seat. Avoid sustained full throttle until the tune has been finalized on a dyno or street log.

Supporting Modifications for Maximum Gains

The Forge IS38 kit is a strong foundation, but to fully unlock its potential, you should consider the following supporting parts:

  • High-Flow Downpipe: 3-inch catted or catless downpipe reduces backpressure and spool time. Mated to a Stage 2 tune, this adds 15–25 whp.
  • Cold Air Intake: An open-element intake (e.g., Forge, IE, Eventuri) helps the turbo breathe. The factory airbox is restrictive above 350 whp.
  • Fuel System Upgrade: The stock high-pressure fuel pump and injectors can support up to ~400 whp on 93 octane. For ethanol blends (E30–E60), you will need a larger low-pressure fuel pump and HPFP (e.g., Autotech or APR).
  • Ethanol Content Sensor and Tune: E85 offers knock resistance and higher octane, allowing more timing advance. Expect 420+ whp with a custom ethanol tune.
  • Stronger Clutch (Manual Transmission): The stock clutch will slip near 380 whp. A Southbend Stage 3 Endurance or Sachs SRE clutch is recommended.
  • Engine Mounts: Vibratechnics or 034Motorsport motor/trans mounts prevent wheel hop and improve throttle response.

Tuning Requirements and Custom Calibration

Do not run the Forge IS38 on a stock tune. The larger turbo will surge and the ECU will pull timing aggressively, potentially causing drivability issues. You have two tuning options:

  • OEM+ Flash Tunes: Companies like Unitronic and APR offer off-the-shelf IS38 files. These are safe and well-calibrated for pump gas with the included intercooler. Gains are 340–370 whp.
  • Custom Tuning via EQT or 034Motorsport: These allow you to dial in boost by gear, adjust cam angles, and optimize for your specific fuel and elevation. A custom tune is essential if you use ethanol or have a manual transmission (to control torque limiters).

Expect to pay $600–$1,200 for a custom tune including remote logging. Choose a tuner experienced with the Forge hardware—they can provide base files that account for the adjustable actuator.

Potential Issues and Solutions

Boost leak at charge pipe connections: The Forge intercooler uses bead-locked ends, but aftermarket charge pipes may require T-bolt clamps. Use a boost leak tester to locate leaks.

Oil leak at the return line: The IS38’s oil return flange can be tricky to seal. Apply a thin layer of RTV silicone (VW spec) to both sides of the gasket.

Wastegate rattle: If the actuator rod is too loose, the wastegate flap will vibrate under high exhaust flow. Adjust preload by tightening the rod 1–2 full turns.

Overboost / boost spike: This is often caused by a stuck open bypass valve or a tune that expects a smaller turbo. Upgrade to a Forge or GFB blow-off valve and have your tuner reduce wastegate duty cycle.

Maintenance and Longevity

The IS38 turbo is robust if properly maintained. Use 5W-40 full synthetic oil changed every 5,000 miles. Replace the spark plugs every 10,000 miles (index one range colder, e.g., NGK 6510). Clean the intercooler core every two years to remove oil residue from blow-by. The Forge intercooler is lifetime-guaranteed against leaks, but the charge pipes should be inspected for cracking after high-mileage use.

Conclusion

The Forge Motorsport S3 IS38 Upgrade Kit delivers proven, reliable power gains for the MQB platform. With careful installation, proper tuning, and quality supporting parts, you can exceed 400 whp on pump fuel and 450 whp on ethanol. The included intercooler eliminates the need for additional heat exchanger upgrades, making this a complete package rather than a piecemeal approach. For enthusiasts who want a daily-driver-capable setup with genuine highway-pulling torque, the Forge IS38 kit is a benchmark upgrade.

Note: Always verify compatibility with your vehicle’s model year and production date. Some 2015–2016 S3s have a different coolant routing; a quick call to Forge can confirm correct part numbers.