The B9 Audi S4 is a formidable machine straight from the factory, but like many turbocharged platforms, its performance potential is limited by heat. The stock intercooler, while adequate for daily driving, quickly becomes a bottleneck during aggressive driving, track days, or after engine tuning. Upgrading to a high-flow intercooler, such as the Wagner Tuning Competition Intercooler (often referred to as the EVO1 or EVO2 depending on revision), is one of the most impactful modifications you can make. This guide covers the costs, the installation process, and the real-world results you can expect from fitting a Wagner Tuning intercooler to your B9 S4.

Why the B9 S4 Needs an Intercooler Upgrade

Before diving into the specifics of the Wagner unit, it's important to understand why the stock intercooler falls short. The factory intercooler is a bar-and-plate design that prioritizes packaging and cost over maximum thermal efficiency. Under sustained boost, intake air temperatures (IATs) rise sharply. Hotter air is less dense, which reduces oxygen content and forces the ECU to pull timing to prevent knock. This results in a noticeable loss of power—often referred to as heat soak. After just a few back-to-back pulls, a stock B9 S4 can lose 20–40 horsepower.

An upgraded intercooler like Wagner's addresses this by increasing core volume, optimizing fin density, and improving airflow distribution. The result is dramatically lower IATs, more consistent power delivery, and the ability to run more aggressive tunes safely.

Wagner Tuning vs. Other Options for the B9 S4

Wagner Tuning is a German brand renowned for high-quality performance cooling products. Their intercooler for the B9 S4 is a direct-fit replacement, meaning no cutting or modification to the crash bar or bumper is required. Competing options include the APR intercooler, Integrated Engineering's (IE) unit, and 034Motorsport's offering. Wagner stands out for its all-aluminum TIG-welded construction, larger core volume (often around 50% more than stock), and excellent fitment. While APR's unit is also popular, Wagner's design tends to offer slightly better heat rejection in sustained runs, especially at higher boost levels. The Wagner unit is also priced competitively, typically falling between $1,200 and $1,500.

Breaking Down the Costs

Budgeting for this upgrade involves more than just the intercooler itself. Here is a detailed cost breakdown for a Wagner Tuning intercooler installation on a B9 S4:

Parts

  • Wagner Tuning Intercooler (EVO1 or EVO2): $1,200 – $1,500. The EVO2 is the latest revision with improved bar design and slightly better cooling.
  • Coolant (if needed for refill): $20 – $40. You may lose some coolant during the swap; use G13 or equivalent. Pentosin or Audi OE is recommended.
  • Optional: Wagner Charge Pipe Kit: $400 – $600. While not required (the stock charge pipes fit the Wagner intercooler), upgrading to Wagner's aluminum charge pipes eliminates the factory plastic pipes and provides a more secure seal under high boost.
  • Zip ties, hose clamps, and sealing grease: $10 – $20. Can be sourced from any auto parts store.

Labor

  • Professional installation: $300 – $500 (3–5 hours at typical shop rates). Many independent Audi specialists or performance shops charge around $100–$150 per hour.
  • DIY cost: $0 (if you have tools; however, consider the cost of a torque wrench if you don't own one).

Total expected outlay: $1,200 – $2,200, depending on whether you install it yourself and if you add charge pipes. For most enthusiasts, the sweet spot is purchasing the intercooler and a bottle of coolant, then doing the install in a weekend.

The Installation Process: A Step-by-Step Guide

Installing a Wagner Tuning intercooler on the B9 S4 is a DIY-friendly job for someone with basic mechanical skills. The process takes 3–5 hours for a first-timer, less if you're experienced. You'll need standard tools (sockets, wrenches, screwdrivers, a trim removal tool, a torque wrench, and maybe an extra set of hands for bumper removal). Below is a detailed breakdown.

Step 1: Preparation and Safety

  • Park the car on level ground and let the engine cool completely. Hot coolant can cause severe burns.
  • Disconnect the negative battery terminal (12V battery in the trunk for B9 S4).
  • Remove the engine cover (it pulls straight up).
  • Have a drain pan ready; you may spill a small amount of coolant from the intercooler connections.

Step 2: Front Bumper Removal

The bumper must come off to access the intercooler. This is the most time-consuming part, but it's straightforward.

  • Remove the screws in the wheel well liners (three per side, Torx T25 or T30).
  • Remove the undertray screws (several 10mm bolts and push pins).
  • Remove the grille trim (if equipped with adaptive cruise control, carefully unclip the sensor bracket).
  • Remove the top radiator cover and the bolts holding the bumper to the fenders (two per side, accessible behind the wheel well liner).
  • With a helper, gently pull the bumper forward and disconnect any remaining sensor connectors (parking sensors, headlight washers, etc.). Place the bumper on a soft surface.

Step 3: Remove the Stock Intercooler

  • Remove the upper charge pipe that connects the intercooler to the throttle body. It is a plastic pipe held by spring clamps. Use a flathead screwdriver to release the clamps.
  • Remove the lower charge pipe connecting the intercooler to the turbo outlet. This can be tight; wiggling helps.
  • Disconnect the connectors for the IAT sensor and the boost pressure sensor from the stock intercooler.
  • The stock intercooler is held in place by two or three bolts (10mm or 8mm, depending on model year) at the top and a clip at the bottom. Remove the bolts, then lift the intercooler upward and out through the bumper opening. It will slide out with some gentle persuasion.
  • If you plan to replace the charge pipe kit, now is the time to remove the factory plastic tubes completely.

Step 4: Install the Wagner Intercooler

  • Transfer the OEM rubber mounting grommets (if any) to the new Wagner intercooler posts. Wagner includes new silicone inserts for a snug fit.
  • Slide the new intercooler into position from below or through the front, aligning the mounting holes. It will seat against the radiator support.
  • Secure the intercooler with the original bolts. Torque to 10 Nm (7 ft-lbs); overtightening can crack the aluminum mounting brackets.
  • Reconnect the IAT and boost pressure sensors. (Tip: lubricate the o-rings with a tiny bit of silicone grease for an easier install and better seal.)
  • Attach the upper and lower charge pipes. If using the stock pipes, ensure they fully click into place and the retaining clips are engaged. If using Wagner's aluminum charge pipes, tighten the T-bolt clamps to 4 Nm (3 ft-lbs) — do not over tighten, as they will clamp the silicone coupler adequately.
  • Double-check all connections. The Wagner intercooler's inlet and outlet are larger than stock, so the stock couplers must be pushed on completely.

Step 5: Reassemble and Refill Coolant

  • Reconnect the bumper harnesses (parking sensors, fog lights, headlight washers, etc.) and carefully reinstall the bumper. Tighten all bumper bolts to specification (usually 8 Nm).
  • Reinstall the wheel well liners, grille trim, and undertray.
  • Top off the coolant reservoir if any coolant was lost. Use a 50/50 mix of G13 and distilled water. Run the engine with the heater on full hot to bleed air out of the system for 10–15 minutes. Check coolant level again.
  • Reconnect the battery negative terminal.

Step 6: Testing and Validation

  • Start the engine and let it idle for a minute. Listen for any air leaks at the charge pipes.
  • Perform a short test drive. Monitor intake air temperatures (IATs) via an OBD2 scanner or the car's lap timer display (if equipped).
  • Under light load, IATs should be near ambient. Under full boost, they should stabilize far lower than stock.

Real-World Results and Performance Gains

The Wagner Tuning intercooler transforms the B9 S4's thermal management. Here are quantified results from owner data and supplier tests:

  • Lower Intake Air Temperatures: On a 70°F day, stock IATs can reach 130°F+ after a third-gear pull. With the Wagner intercooler, IATs typically peak around 95–105°F, representing a 25–35°F drop.
  • Horsepower Gains (without tune): Even on a stock tune, lower IATs prevent timing pull, recovering 10–15 hp that would otherwise be lost due to heat soak. On a stage 1 or stage 2 tune, dyno tests show gains of 20–30 whp and 25–35 lb-ft of torque, specifically in the mid-range and sustained high-rpm pulls.
  • Consistency: The most significant improvement isn’t peak power but repeatability. A stock B9 S4 will pull power after every hard run. With the Wagner intercooler, power remains consistent run after run — crucial for drag racing, track days, or spirited canyon driving.
  • Throttle Response: Reduced pressure drop across the intercooler leads to quicker spool and more immediate throttle response. Many owners report that the car feels "sharper" and more eager to rev.
  • Long-term Reliability: Lower IATs reduce the risk of engine knock and allow the ECU to run more advanced timing, which is safer for engine components. This is especially important if you have a tuned car pushing over 450 whp.

Who Should Consider This Upgrade?

This upgrade is ideal for:

  • B9 S4 owners who track their car or frequently perform hard acceleration runs.
  • Those with a stage 1 or stage 2 tune who want to maximize and protect their power gains.
  • Drivers in hot climates (summer temps over 90°F) where stock IATs skyrocket.
  • Anyone planning to upgrade the turbo or run ethanol blends (with proper fueling).

If you use your S4 primarily for commuting and never push it hard, the stock intercooler is probably sufficient. But if you want the car to perform at its best every time you press the throttle, the Wagner intercooler is a top-tier choice.

Additional Considerations

While the Wagner intercooler alone is a great step, pairing it with a Wagner charge pipe kit prevents stock plastic pipes from popping off under high boost (a known issue with tuned cars). Also consider upgrading the heat exchanger for the charger cooler circuit if you have a supercharged engine (not applicable for B9 S4, which is turbocharged). Lastly, an ECU tune from brands like APR, Integrated Engineering, or 034Motorsport will fully unlock the potential of the upgraded cooling.

Final Verdict

Installing a Wagner Tuning intercooler on a B9 Audi S4 is a well-proven mod that delivers tangible, measurable benefits. The install is manageable for a DIYer with patience and basic tools, and the cost is reasonable for the performance return. You'll get cooler intake temperatures, consistent power, and increased safety margin for future modifications. For any enthusiast serious about extracting the most from their B9 S4, this is a must-do upgrade.