The Audi A4 2.0T has long been a favorite among enthusiasts who appreciate a balance of refined luxury and spirited performance. Under the hood, the turbocharged 2.0-liter four-cylinder engine offers a solid foundation for increasing power, but the stock turbocharger itself is often the limiting factor. For those looking to extract significantly more horsepower and torque without swapping the entire engine, upgrading the turbocharger is the single most effective modification. ATS Turbo has established itself as a go-to source for precision-engineered turbo upgrades tailored specifically for the Audi 2.0T EA888 and EA113 platforms. This article provides an in-depth look at the best turbo upgrades from ATS Turbo for the Audi A4 2.0T, along with the supporting modifications and tuning required to maximize their potential.

Why Upgrade the Turbo on the Audi A4 2.0T?

The stock turbocharger on the Audi A4 2.0T, typically a BorgWarner K03 or similar small-frame unit, is designed to provide decent low-end torque and acceptable fuel economy for daily driving. However, its compressor and turbine wheels are physically small, which limits the volume of air it can move at higher boost pressures. Beyond about 270–300 wheel horsepower on the 2.0T, the stock turbo becomes inefficient, generating excessive heat and requiring high boost levels that push the engine toward knock limits. Upgrading to a larger or hybrid turbocharger addresses these bottlenecks in several key ways.

  • Sustained high-flow output: Larger turbine and compressor wheels can flow substantially more air, enabling power outputs from 350 to over 500 horsepower depending on the turbo chosen.
  • Reduced heat soak and IATs: More efficient compressors move air with less energy wasted as heat, helping to keep intake air temperatures (IATs) lower under sustained load.
  • Enhanced mid-range and top-end power: While a larger turbo may have slightly higher boost threshold, the power delivery becomes linear and pulls hard all the way to redline, transforming the driving experience.
  • Improved response with hybrid designs: Modern hybrid turbos incorporate billet wheels and optimized housings to reduce spool time, providing near-stock responsiveness with significantly more peak power.

Before selecting a specific upgrade, it is important to define your target power level and driving use. A track-focused weekend car can accept a larger frame with slower spool, while a daily driver needs strong torque from low RPMs. ATS Turbo offers options that cater to both ends of the spectrum.

Understanding Your Goals: Power Levels and Driving Needs

The Audi A4 2.0T engine comes in several iterations, including the EA113 (found in earlier B7 models) and the EA888 series (B8, B8.5, B9). The platform has a robust bottom end but loses head gasket integrity and connecting rod strength above certain torque thresholds. ATS Turbo’s upgrades are matched to appropriate power bands:

  • Stage 1+ (350–380 whp): Ideal for a daily driver with upgraded fueling, intercooler, and a K04-style hybrid. Requires no internal engine modifications.
  • Stage 2 (400–450 whp): Requires a GT28RS or similar frame, plus larger injectors, a high-flow fuel pump, and an upgraded intercooler. Forged rods are recommended for sustained use.
  • Stage 3 (450–550+ whp): Full-frame turbos like the GTX3071R or larger. Requires built bottom end, port injection, and aggressive tuning. Best suited for cars used primarily for track or drag racing.

Most ATS Turbo offerings fall into the Stage 1+ and Stage 2 categories, offering substantial gains with acceptable daily drivability.

Top ATS Turbo Upgrades for the Audi A4 2.0T

ATS K04 Turbo Upgrade

The K04 is one of the most popular turbo upgrades for the Audi 2.0T, and ATS Turbo’s version refines the design to maximize flow and reliability. Using a larger compressor wheel than the stock K03, the ATS K04 fits directly into the factory location with minimal modification. It is capable of supporting up to approximately 370 wheel horsepower on pump gas with proper tuning.

Key features: Direct bolt-on replacement; requires no manifold or downpipe modification; works with stock or upgraded software from tuners like Unitronic or APR; spools nearly as quickly as the stock turbo. The ATS K04 is an excellent choice for owners who want a significant power increase without the complexity of a full-frame turbocharger install. It retains the factory-like spool character, delivering strong mid-range torque that makes it ideal for daily driving and spirited back-road use.

To reach the higher end of its potential, add a high-flow downpipe, cold air intake, and front-mount intercooler. A custom tune that pushes boost to around 23–24 psi is typical, requiring 93 octane or equivalent. For those on a budget, the ATS K04 offers the best power-per-dollar for a 350+ whp goal.

ATS GT28RS Turbo Upgrade

For enthusiasts seeking a true step up in airflow capacity, the ATS GT28RS is a Garrett-based upgrade that delivers exceptional efficiency. The GT28RS (commonly known as the “Disco Potato” in tuning circles) features a 52-trim compressor and a .64 A/R turbine housing that provides a balance of quick spool and high flow. On the Audi 2.0T, this turbo supports up to 440 wheel horsepower with proper fueling.

Key features: Requires an upgraded manifold (often the stock unit is modified or replaced); uses a T25 or T3 flange; spools by 3200–3500 rpm under load; supports high boost levels well past 30 psi. The ATS GT28RS upgrade kit typically includes the turbocharger, oil and coolant lines, gaskets, and a compatible downpipe adapter. This setup pulls hard from 4000 rpm to redline, making it a favorite for roll racing and high-speed driving.

Because the GT28RS moves much more air than a K04, supporting modifications are non-negotiable. A larger intercooler (at least 2.5″ core) is required to keep IATs under control, and the fuel system must be upgraded with high-flow injectors (e.g., 550cc or larger) and an in-tank fuel pump. An aftermarket intake with a 4″ inlet helps the turbo breathe freely. With a quality tune from a specialist like EQT or Stratified, the GT28RS delivers linear power without the torque spike that can stress rods.

ATS TTE420 Hybrid Turbo

The TTE420 is a hybrid turbocharger built by TTE Systems (Turbotechnics) and offered through ATS Turbo. It combines a K04-style turbine housing with a larger billet compressor wheel and upgraded internals. The TTE420 is engineered to bridge the gap between a conventional K04 and a full GT28RS, offering strong spool and a broad power band up to around 420 horsepower (hence the name).

Key features: Bolt-on K04 housing fits directly to the stock manifold; billet 6+6 compressor wheel for faster response; reinforced thrust bearing for reliability; supports up to 400–420 whp with a tune and supporting mods. The TTE420 is particularly popular among owners who want a responsive daily driver with enough top-end to embarrass larger-engined competitors. Spool is nearly identical to a K04, but the flow plateau extends several hundred rpm higher, giving the engine a more aggressive top-end punch.

Installation is nearly identical to a K04 swap, but users should upgrade the intercooler and intake. Because the TTE420 pushes more boost pressure at high rpm, a high-flow catalytic converter or downpipe helps lower backpressure. The TTE420 is often paired with a stage 2+ tune and supports ethanol blends, which can push power beyond 420 whp safely if the fuel system is upgraded.

Critical Supporting Modifications for a Turbo Upgrade

Installing a larger turbocharger without addressing the supporting hardware is like upgrading the engine of a car while leaving the stock brakes and tires. To safely deliver the increased airflow and the resulting power, the following modifications are essential:

Fuel System Upgrades

The stock high-pressure fuel pump (HPFP) on the EA113 and early EA888 engines is marginal for power above 300 whp. An upgraded HPFP, such as the Autotech or APR pump, increases fuel rail pressure and prevents fuel starvation under high boost. Low-pressure fuel pumps should also be upgraded when exceeding 400 whp. Larger injectors (e.g., Bosch 550cc or 630cc) are required for GT28RS and TTE420 turbos to maintain proper air-fuel ratios.

Intercooler Upgrade

An upgraded front-mount intercooler (FMIC) is mandatory for any turbo upgrade beyond the stock K03. The factory side-mount intercooler is restrictive and prone to heat soak after a few hard pulls. A stepped-core FMIC with efficient bars-and-plate design reduces IATs by 30–50°F under load, preventing knock and maintaining combustion stability. Many ATS Turbo customers pair their turbo with a high-capacity intercooler from brands like Wagner Tuning or Forge Motorsport.

Exhaust and Intake Flow

A turbo can only breathe as well as the system around it allows. A 3″ downpipe (with or without a high-flow catalytic converter) eliminates the factory restriction and is essential for spool and top-end flow. Pair it with a 3″ cat-back exhaust for optimal flow. On the intake side, a cold air intake with a large filter and smooth piping reduces pressure drop before the compressor inlet, helping the turbo spool faster. For GT28RS and larger turbos, a 4″ intake is preferred.

Engine Management and Tuning

No turbo upgrade should be attempted without a custom tune or a well-matched off-the-shelf calibration from a reputable tuner. The stock ECU parameters cannot compensate for the higher airflow, altered MAF readings, and different boost characteristics. Tuning is where the power gains are truly realized—improper calibration can lead to knock, excessive EGTs, and mechanical failure. ATS Turbo works with several tuning partners, and many owners opt for remote tuning solutions from specialists like United Motorsports or Integrated Engineering.

Tuning Your Audi A4 2.0T After a Turbo Upgrade

Once the new turbo and supporting hardware are installed, the engine control unit (ECU) must be reprogrammed to manage boost targets, fueling, ignition timing, and throttle response. Tuning is the most critical phase of the upgrade process. Without proper calibration, the engine may run lean or detonate under load, leading to catastrophic failure.

Selecting a Tuner

Three common routes exist: off-the-shelf (OTS) tunes from major brands like Unitronic, APR, or GIAC; base maps provided by the turbo supplier; or custom remote tuning. For the ATS K04, OTS tunes are well developed and provide reliable, safe power. For the GT28RS and TTE420, custom tuning is recommended because the airflow varies with each engine build. A tuner can adjust fuel maps for ethanol blends, set boost thresholds for driveability, and program more aggressive torque reduction for rod protection.

Dynamic Parameters

A good tuner will target a linear torque curve rather than an early peak that can overstress connecting rods. Boost is typically tapered from around 26 psi at low rpm to 20–22 psi at redline. Ignition timing is advanced up to the point of knock detection, and fuel trims are optimized for the larger injectors. Many modern tunes also incorporate flex-fuel capability, allowing the car to run pump gas or E85 with automatic adjustments. E85 is especially effective for turbo upgrades as it provides knock resistance and allows higher boost.

Post-Tune Validation

After the initial tune, a data log session (logged via tools like VCDS or Cobb Accessport) should be performed to verify boost, air/fuel ratio (target 11.5–12.0:1 on pump gas), and ignition timing. Any abnormal knock counts or fuel pressure drops indicate a need for further calibration or hardware upgrades. It is wise to have the car dyno-tuned to peak power and ensure that all systems work in harmony.

Installation Considerations

Installing a turbocharger on the Audi A4 2.0T is a moderately complex job that requires mechanical skill and patience. While the ATS K04 and TTE420 are nearly direct bolt-ons, the GT28RS demands manifold modification. Here is a general installation overview and important preparatory steps:

  • Preparation and workspace: Gather all necessary tools—torque wrench, E-socket set, coolant and oil, new gaskets, and antiseize compound. A service manual or online guide from a trusted forum (like Audizine or AudiWorld) will help with torque specs.
  • Remove the stock turbo: Drain the coolant and oil, then disconnect the exhaust downpipe, intake pipes, and charge air hoses. Unbolt the turbo from the manifold and remove the oil and coolant lines. Take care not to strip the EGT sensor or O2 sensor threads.
  • Inspect and clean: Before installing the new turbo, inspect the manifold for cracks, clean the mating surfaces, and ensure all oil feed and return lines are free of debris. Replace copper crush washers and gaskets.
  • Install the new turbo: Position the new turbo with the gasket and torque bolts to spec. Attach oil feed and return lines, coolant hoses, and the wastegate actuator. For GT28RS setups, you may need to install the turbo on the manifold before mounting the manifold to the head.
  • Reassemble and check: Reconnect downpipe, intake, and intercooler piping. Fill the cooling system and prime the turbo by cranking the engine with the fuel pump fuse removed (or temporarily disabling injection) to circulate oil before startup. Start the engine, check for leaks, and monitor oil pressure.

Overlooked details like proper torque of the banjo bolts or using thread-locker on the actuator bracket can cause problems down the line. A professional installation by a shop experienced with Audi 2.0Ts is a wise investment if you lack the tools or confidence.

Reliability and Maintenance Post-Upgrade

A turbocharged engine that has been upgraded to produce 350–450 horsepower demands more rigorous maintenance than a stock car. Improving reliability involves attention to cooling, lubrication, and fuel quality:

  • Frequent oil changes: Use a high-quality full synthetic 5W-40 or 0W-40 oil with a short change interval of 3,000–5,000 miles. The turbocharger’s increased heat and speed place more stress on the oil’s film strength.
  • Cooling system: Upgrade the radiator to a thicker core or add an oil cooler if you push the car hard on track. The stock cooling system may be adequate for street use, but sustained high-load runs can cause overheating.
  • Monitoring: Install a boost gauge, oil temperature gauge, and wideband air-fuel ratio sensor to track vitals. A unit like the P3Cars vent gauge integrates with the Audi dashboard.
  • Spark plugs: Use a one-step colder spark plug (e.g., NGK BKR7EIX or Denso IK27) to prevent pre-ignition under high boost. Gap them to manufacturer specifications for your tune.
  • Fuel quality: Always run premium fuel with the highest octane available. If using E85, test the ethanol content and ensure your injectors and pump are adequate.

Regular checks for boost leaks (from charge pipes and intercooler couplers) and vacuum leaks (from PCV system) will keep the engine running smoothly. The ATS Turbo products are built with quality bearings and seals, but no turbo is immune to damage from contaminated oil or debris.

Conclusion

Upgrading the turbocharger on your Audi A4 2.0T unlocks a level of performance that transforms the car from a competent luxury sedan into a genuine sports machine. ATS Turbo provides three excellent paths forward: the straightforward ATS K04 for a responsive daily driver up to 370 whp, the potent ATS GT28RS for those chasing 400+ whp with a focus on top-end flow, and the refined TTE420 hybrid for a balance of spool and high flow. Each upgrade requires careful selection of supporting modifications—fuel system, intercooler, exhaust, and a quality tune—to deliver reliable power that can be enjoyed for years. By matching the turbo to your power goals and investing in proper installation and maintenance, the Audi A4 2.0T becomes a genuinely fast car that still retains all its everyday usability.

For more details on turbo options and kit contents, visit ATS Turbo. For tuning support and community knowledge, forums like Audizine and AudiWorld are invaluable. Supporting components can be sourced from reputable suppliers such as ECS Tuning for intercoolers, downpipes, and fuel parts.