The Ultimate S3 IS38 Turbo Upgrade: Unlocking 50-70 HP with the APR Stage 2 Kit

The Audi S3 (8V and 8Y) and its Volkswagen Golf R cousin are already stout performers from the factory, but the 2.0 TFSI engine has hidden potential that can be unleashed with a turbocharger upgrade. The IS38 turbocharger, sourced from the Audi RS3 and TTRS, is the most common and effective single-turbo upgrade for the MQB platform. When paired with a comprehensive APR Stage 2 kit, the results are nothing short of transformative: reliable gains of 50-70 horsepower at the wheels, along with significantly more torque across the entire rev range. This guide provides a deep dive into what this upgrade entails, from the hardware to the software, and what you can expect in terms of performance, driveability, and long-term reliability.

Why the IS38 Turbocharger?

The factory IHI IS20 turbocharger on the S3 is competent, but it runs out of steam in the upper mid-range and top end. The IS38 features a larger compressor wheel and turbine housing, allowing it to push more air volume at higher boost pressures. This translates directly to higher peak horsepower figures. The IS38 is a direct bolt-on replacement for the IS20, meaning it mounts to the same exhaust manifold and uses the same oil and coolant lines. This makes it an attractive upgrade for DIY enthusiasts, though professional installation is recommended for optimal results.

Key Specifications and Design Differences

  • Compressor Wheel: The IS38 uses a larger 51mm (approx) billet compressor wheel vs. the IS20's 45mm wheel, moving more air per revolution.
  • Turbine Wheel: The turbine wheel is also increased in size (from 44mm to 48mm), which helps reduce backpressure at high flow rates.
  • Housing: The turbine housing A/R (area/radius ratio) is optimized for higher flow, shifting the powerband higher without sacrificing spool characteristics entirely.
  • Boost Threshold: With the correct tuning, full boost can arrive as early as 3200-3500 RPM, offering a broad powerband rather than a peaky top-end.

The APR Stage 2 Kit: More Than Just Software

The APR Stage 2 kit is a complete hardware and software package designed to extract the maximum safe power from the IS38 turbocharger on a largely stock internal engine. Unlike a Stage 1 tune (which only replaces software), Stage 2 adds essential hardware upgrades to manage the increased heat and airflow. The kit typically includes:

Core Components

  • APR High-Flow Intercooler System: The stock intercooler becomes heat-soaked after one or two hard pulls. The APR unit is a 4" thick bar-and-plate core that reduces intake air temperatures (IATs) by 30-40°F, preventing power loss in hot weather and during repeated runs.
  • APR Closed Carbon Fiber Intake System: Replaces the restrictive stock airbox with a high-flow intake that draws cold air from the front bumper. It reduces intake restriction and provides a satisfying induction sound.
  • APR Performance Exhaust System (or Downpipe with Tune): The Stage 2 tune requires a free-flowing downpipe (typically 3" to 3.5") with a high-flow catalytic converter or a full turbo-back exhaust. APR offers both a catback and a full exhaust system. The downpipe alone is responsible for a significant portion of the power gains.
  • APR ECU Upgrade (Stage 2 IS38 Tune): This is the brain of the operation. The tune recalibrates boost control, fuel delivery, ignition timing, and throttle mapping to match the increased airflow of the IS38 and the exhaust/cooling upgrades.

Real-World Performance Gains: Dyno Charts & Acceleration

On a 93-octane or EU 98-RON fuel map, a properly installed IS38 turbocharger with APR Stage 2 hardware and software typically produces between 370 and 390 wheel horsepower (whp) and 370-390 lb-ft of torque on a Dynojet chassis dynamometer. That's roughly 100-110 whp gain over a stock S3 (which makes about 270-280 whp at the wheels). The engine rpm range that sees the most improvement is from 4000 to 7000 RPM, where the IS38 pulls strongly to redline without dropping off.

0-60 and Quarter-Mile Improvements

  • 0-60 mph: Stock S3: ~4.5-4.7 seconds. With IS38 + APR Stage 2: ~3.5-3.7 seconds (with good traction and DSG launch control).
  • Quarter-Mile: Stock S3: ~12.9-13.2 seconds. With IS38 + APR Stage 2: ~11.6-11.9 seconds at 115-118 mph trap speed.

These numbers are consistent across many owner reports and independent testing. For an in-depth dyno comparison, check out APR's official Stage 2 product page for their own chart and notes.

Installation: A Step-by-Step Overview

While not incredibly complex, installing the IS38 turbocharger and APR Stage 2 kit requires a solid mechanical understanding and a well-equipped garage. The entire process can take 6-12 hours for an experienced technician. Here's a high-level breakdown:

  1. Preparation: Disconnect the battery, drain engine coolant and oil, remove the intake manifold and charge air pipes.
  2. Downpipe Removal: The factory downpipe is held on by four nuts to the turbo outlet. This step is often the most rusted and stubborn part of the job. A torch and penetrating oil are recommended.
  3. Intercooler Swap: Remove the front bumper and crash bar to access the stock intercooler. Replace with the APR unit, ensuring all charge air connections are sealed.
  4. Turbocharger Swap: Remove the IS20 turbo (oil feed line, coolant lines, V-band clamp, and bolts). Install the IS38 with a new gasket and O-rings. Torque all fasteners to spec.
  5. Intake and Exhaust: Install the APR intake and performance catback exhaust (or downpipe). Route the intake to the front grille area.
  6. Software Flashing: Use an APR dealer or the APR Mobile device (if you have the correct hardware) to flash the Stage 2 IS38 tune. Follow the calibration procedure for the intake and intercooler if required.
  7. Test Drive: Start the engine and check for leaks. Perform a gentle drive cycle to let the engine learn the new parameters. Then, conduct a few full-throttle pulls in a safe area.

For a more detailed guide with torque specs and cautions, Audizine's IS38 swap guide is a trusted community resource.

Tuning Considerations & Fuel Requirements

APR offers multiple fuel octane programs for the IS38 Stage 2 tune: 91, 93, and 100 octane (or corresponding RON). For maximum power, 93 octane (or 98 RON) is recommended. Using 91 octane will result in slightly lower peak power (by about 10-15 whp) due to the engine pulling timing to avoid knock. E85 is another option for those with flex-fuel kits, but that requires further upgrades (fuel pump, injectors, high-pressure fuel pump). The Stage 2 IS38 tune also includes launch control, no-lift shift, and adjustable throttle response.

Supporting Modifications for Reliability

While the APR Stage 2 kit is comprehensive, some S3 owners add further supporting mods for peace of mind:

  • Upgraded PCV System: The stock PCV can blow under high boost, leading to valve cover gasket failure. A catch can or upgraded PCV is often recommended.
  • High-Pressure Fuel Pump (HPFP): For cars running high ethanol blends or aggressive tuning on 93 octane, a HPFP upgrade ensures fuel pressure doesn't drop at high RPM.
  • Transmission Tune (DSG): The S3's 6-speed DSG can handle the torque, but a Stage 2 DSG tune (e.g., APR DSG tune) sharpens shift speed and increases torque limits.
  • Engine and Transmission Mounts: Stiffer mounts reduce wheel hop and improve traction during hard launches.

Drivability & Day-to-Day Experience

Despite the large power increase, the IS38 + APR Stage 2 kit is surprisingly civilized. The car remains quiet and smooth when driven sedately. The APR intercooler prevents heat soak in stop-and-go traffic, and the intake noise is only audible under hard throttle. The torque curve is broad, which means you don't have to downshift constantly; the car pulls strongly from around 3000 RPM in top gear. This makes it a fantastic daily driver that can transform into a track-day weapon on a twisty road. The improved throttle response from the tune makes the car feel more eager and immediate.

Common Questions and Misconceptions

Will the IS38 + Stage 2 kill the engine?

No, not if installed correctly and tuned properly. The 2.0 TFSI (EA888 Gen3) is a strong engine. The weak points are the connecting rods and ring lands when boost levels exceed 26-27 psi on pump gas. APR's tune stays within safe limits (typically around 24-26 psi peak) to preserve reliability. Most owner-reported failures occur due to improper tuning (e.g., running too much boost without adequate fuel) or pre-existing issues. The APR tune is known for being conservative with fuel trims and ignition timing.

Do I need an upgraded intercooler with the IS38?

Yes, absolutely. Without an upgraded intercooler, intake air temperatures will skyrocket, causing the ECU to pull timing and reduce power significantly. The APR high-flow intercooler is a critical component of the Stage 2 kit. Running the IS38 with the stock intercooler is not recommended.

Can I use the factory downpipe with the APR Stage 2 tune?

The APR Stage 2 tune is designed for a high-flow downpipe. Using the stock downpipe will cause the turbo to choke, reduce power, and potentially cause boost spikes. A downpipe is mandatory.

What's the cost of the full upgrade?

Ballpark, expect to spend between $3,500 and $5,000 for the turbo, intercooler, intake, downpipe, software, and labor (dealer installation). The APR kit pricing can be found on APR's official site. You can often find slightly used IS38 turbos for a good price, but ensure they come from a reputable source.

Conclusion: Is It Worth It?

The Audi S3 IS38 turbo upgrade paired with the APR Stage 2 kit is one of the best value performance modifications for the MQB platform. For a moderate investment, you gain a reliable 50-70 wheel horsepower boost, transforming the S3 into a true pocket rocket that can challenge some dedicated sports cars. The drivability remains excellent, and the installation, while moderately challenging, is well-documented. Whether you're looking for a weekend toy or a rapid daily, this combination delivers thrilling result with minimal compromise. As with any performance upgrade, use quality parts and respect the tuning parameters, and you'll enjoy hundreds of thousands of miles of boosted driving.