Why Upgrade to the BSH S3 IS38 Turbo?

The BSH S3 IS38 turbocharger upgrade is a well-known modification for owners of the Audi S3, Volkswagen Golf R, and other MQB-platform 2.0T vehicles. The factory turbocharger on these cars (typically the IHI IS20 or a smaller K03 variant) limits peak horsepower to around 290–310 whp with a Stage 1 tune. The IS38, originally found on the Audi S3 8V and Golf R MK7, flows significantly more air and can support upwards of 400 whp with proper fueling and tuning. The BSH variant offers a direct replacement with OEM-quality castings and upgraded internals, making it a reliable choice for enthusiasts who want a straightforward install and predictable gains. This guide will walk you through the entire DIY installation, which most experienced home mechanics can complete in about 60 minutes if they have the right tools and preparation.

What You Need: Tools, Parts, and Supplies

Before you begin, gather everything in one place. Running back and forth for a missing socket will break the 60-minute pace. The following list covers the essentials.

Tools

  • Socket set: metric sizes from 8mm to 16mm, including 10mm, 13mm, and 16mm
  • Torque wrench capable of 15–50 Nm (10–35 ft-lb) for turbo bolts and banjo fittings
  • Flathead and Phillips screwdrivers (for hose clamps and electrical connectors)
  • Pick tools or small pry bar for stubborn clips
  • VAGCOM (VCDS) or a high-quality OBD-II scanner (e.g., OBDeleven) for clearing codes and performing adaptations
  • Jack and jack stands or a lift (optional but recommended for access)
  • Safety glasses and mechanic’s gloves

Parts & Supplies

  • BSH S3 IS38 turbo upgrade kit – includes the turbocharger and any necessary fittings. Verify your kit comes with a new actuator or that you reuse your factory actuator.
  • New gaskets: turbo-to-manifold gasket, turbo-to-downpipe gasket, and oil feed/drain gaskets. Some kits include them; if not, order OEM equivalents.
  • Coolant (G13 or your vehicle’s spec) for topping off after coolant line removal
  • Engine oil (5W-40 or 0W-40 meeting VW 502/504 spec) for post-install fill
  • Anti-seize compound (copper or nickel) for exhaust manifold studs
  • Thread locker (blue Loctite 242) for critical bolts

Preparation: Safety and Access

Park and Cool

Park the vehicle on a level surface. If you use ramps, ensure they are rated for the weight. The engine and exhaust manifold must be completely cool to avoid burns and to allow the turbo bolts to come out without binding. Wait at least 2 hours after shutdown or work on it first thing in the morning.

Disconnect the Battery

Remove the negative battery terminal using a 10mm socket. This prevents accidental short circuits when unplugging electrical connectors near the turbo (e.g., the wastegate actuator, knock sensor, or O2 sensors). It also resets the ECU adaptations, which is helpful before a new turbo install.

Remove the Engine Cover and Air Intake

Pop off the engine cover by hand or with a trim tool. Disconnect the mass airflow sensor (MAF) and remove the intake pipe from the turbo inlet. You do not need to remove the entire airbox, but doing so frees up room. Use a 10mm socket to unbolt the battery tie-down if you need to slide the battery aside for better access to the turbo area.

Removing the Factory Turbocharger

The turbocharger uses coolant lines that carry pressurized coolant. To minimize mess, drain about 2 liters of coolant from the radiator petcock or disconnect the lower radiator hose. Alternatively, you can clamp the hoses before removal, but this risks air pockets. Draining gives you clean access and lets you replace with fresh coolant.

Step 2 – Remove Exhaust System Components

You will need to disconnect the downpipe from the turbo. Use a 16mm socket to remove the three bolts holding the downpipe to the turbo flange. On some vehicles, you may need to unbolt the downpipe from the catalytic converter mount. Then unbolt the exhaust hanger near the transmission to drop the downpipe down. This gives clearance to slide the turbo out from below.

Step 3 – Unplug Electrical Connections

  1. Disconnect the wastegate actuator connector (usually a two-pin plug near the compressor housing).
  2. Unplug the O2 sensor on the downpipe (if still connected).
  3. If your vehicle has a turbo speed sensor or a diverter valve harness, disconnect those as well.

Step 4 – Remove Coolant and Oil Lines

Use a 10mm socket or wrench to remove the coolant banjo bolts on the turbo. Be prepared for spilled fluid. Remove the oil feed line from the top of the turbo (usually a 16mm or 18mm banjo). Then remove the oil drain line from the bottom of the turbo (two 10mm bolts). Keep the line clear of debris; plug the drain hole on the block with a clean rag.

Step 5 – Unbolt the Turbo from the Manifold

The factory turbo is attached to the exhaust manifold with three or four studs and nuts (10mm or 13mm). Apply penetrating oil and wait 5 minutes if they are rusty. Use a 13mm socket and ratchet with an extension to reach the lower nuts. Remove all nuts and carefully lift the turbo out of the engine bay. You may need to wiggle it past the subframe.

If it sticks, check for hidden bolts or clips. Do not pry forcefully on the compressor housing—it is cast aluminum and can crack.

Installing the BSH S3 IS38 Turbo Upgrade

Step 6 – Prepare the Mounting Surfaces

Clean the exhaust manifold flange and the turbo mounting face with a brass brush and brake cleaner. Install new gaskets: one on the exhaust manifold (if the turbo uses a separate gasket) and one on the downpipe flange. Apply a thin coat of anti-seize to all exhaust manifold studs and threads. This prevents galling and makes future removal easier.

Step 7 – Position and Bolt the Turbo

Lower the BSH IS38 turbo into place. Align the oil feed line and coolant banjo holes. The turbo may need to be rotated slightly to line up with the studs. Hand-tighten the manifold nuts, then torque them to the manufacturer’s spec. If no spec is provided, use 22 Nm (16 ft-lb) for M8 nuts and 35 Nm (26 ft-lb) for M10 nuts.

Apply blue Loctite to the threads to prevent loosening from vibration.

Step 8 – Reattach Oil and Coolant Lines

  1. Install the oil drain line with a new gasket. Torque to 10 Nm (7 ft-lb).
  2. Install the oil feed line banjo bolt. Use new copper washers on both sides of the fitting. Torque to 25 Nm (18 ft-lb).
  3. Reconnect coolant lines with new gaskets. Torque banjo bolts to 20 Nm (15 ft-lb).

Pro tip: Use a mirror and a flashlight to verify that the drain line is not kinked. A kinked oil drain can starve the turbo of lubrication and cause failure within minutes.

Step 9 – Reconnect Electrical Connectors and Downpipe

Plug in the wastegate actuator, O2 sensors, and any other connectors. Double-check that each clicks securely. Install the downpipe onto the turbo flange with new gasket. Torque the three bolts to 28 Nm (20 ft-lb). Reattach the exhaust hangers and any brackets you removed.

Step 10 – Refill and Reconnect

  • Reinstall the intake pipe and MAF sensor.
  • Pour fresh coolant up to the correct level. Use a 50/50 mix of G13 or equivalent.
  • Fill the engine with oil (if you drained it) to the proper amount (typically 5.5-6.0 liters for a 2.0T). Do not overfill.
  • Reconnect the battery negative terminal.

Post-Installation: Check, Prime, and Tune

Prime the Turbo

Before starting the engine, you need to pre-lubricate the turbo bearings. Disconnect the ignition coil harness (so the engine can crank without firing) or pull the fuel pump fuse. Crank the engine for 10 seconds. This builds oil pressure and pushes oil through the turbo. Reconnect the ignition harness or reinstall the fuse.

Start and Inspect

Start the engine. Let it idle for about 30 seconds. Listen for unusual noises like whining or grinding (indicates a problem). Check under the car for oil or coolant drips. Do not rev the engine above 2,000 RPM for the first minute. Let the turbo heat cycle slowly.

Use your OBD-II scanner to check for DTCs. There may be a soft code due to battery disconnect; clear them all. Also verify that the wastegate actuator moves freely (you can do a VCDS output test).

Tuning Requirements

Installing a larger turbo without a corresponding ECU tune will cause issues: the engine will run lean, knock, or go into limp mode. You must have a quality tune designed for the IS38. Options include:

  • Unitronic IS38+
  • APR IS38
  • Custom tuning via EQT, Eurodyne, or a local tuner

If you already had a Stage 2 file for the IS20, you cannot simply reuse it. Flash the correct IS38 file before driving the car hard.

Common Mistakes and How to Avoid Them

  • Not replacing gaskets: Reusing old gaskets causes exhaust leaks, oil leaks, and boost loss. Always fit new ones.
  • Over-tightening turbo bolts: Cast iron and aluminum have different expansion rates. Follow torque specs to avoid snapping a stud.
  • Leaving air in coolant system: After refill, run the engine with the coolant cap off until the thermostat opens. Add coolant as needed.
  • Skipping the oil prime: This is the #1 cause of premature turbo failure. Always prime.
  • Ignoring wastegate calibration: After install, the wastegate arm may need adjustment to achieve proper boost levels. Use a VCDS to log actual vs. requested boost.

Performance Expectations and Maintenance

With a proper tune, the BSH S3 IS38 upgrade delivers a noticeable power increase from 3,500 RPM to redline. Typical gains are 80–100 whp over stock, depending on supporting mods (intercooler, downpipe, intake). Boost pressure will be in the 24–28 psi range. The turbo spools slightly slower than the IS20 but pulls hard to redline.

Maintenance: Change oil every 5,000 miles with high-quality synthetic. Check downpipe bolts for loosening after 500 miles. Do not run low on oil – journal-bearing turbos do not tolerate oil starvation.

For further reading, check out the BSH official product page (BSH S3 IS38 Turbo Upgrade Kit), the comprehensive install thread on GolfMK7 (IS38 Installation Guide), and the Ross-Tech VCDS wiki (VCDS Tour) to get the most out of your scan tool.

Final Word

The BSH S3 IS38 upgrade is an achievable afternoon project for anyone with basic mechanical skills and the right tools. By following the steps above—preparation, removal, careful installation, and post-work checks—you can complete the job in about 60 minutes as advertised. The result is a transformed driving experience with significantly more power across the rev range. Always verify all connections and use a proper tune to protect your investment. If you encounter unexpected resistance, consult a professional or search dedicated VW/Audi forums.

Safe wrenching.