The Audi RS5 has long been a benchmark in the compact performance coupe segment, offering a compelling mix of everyday usability and genuine sports car capability. Under the hood of the latest-generation models (B9 and B9.5) lies the 2.9-liter twin-turbo V6, a force-fed masterpiece that delivers 444 horsepower and 443 lb-ft of torque straight from the factory. While that output is more than sufficient for most driving scenarios, serious enthusiasts know that the RS5’s engine is built to handle significantly more. Aftermarket tuning specialists like APR have developed a series of performance packages that unlock this hidden potential. Among these, the APR Stage 2 kit stands out as a transformative upgrade, promising gains in the region of 60 horsepower, along with substantial increases in torque and throttle response. This article provides a detailed technical and practical overview of the APR Stage 2 kit for the Audi RS5, covering the hardware, the tuning, installation considerations, and real-world performance results.

The Engine and Its Potential

The 2.9 TFSI V6, designated EA839, is shared across several Audi and Porsche models. It features a hot-vee architecture with twin turbochargers nestled in the valley of the engine block. This design reduces turbo lag and improves spool characteristics, but it also creates a heat-intensive environment. The turbochargers themselves are surprisingly capable, but the factory calibration leaves a significant safety margin. With an upgraded software remap and a few key hardware changes, the engine can safely produce over 500 horsepower on pump fuel. The APR Stage 2 kit leverages this headroom by improving both the engine’s ability to breathe and its ability to manage higher boost pressures and combustion temperatures.

From Stage 1 to Stage 2 – The Upgrade Path

Before diving into Stage 2, it is worth understanding the stages offered by APR. Stage 1 involves only an ECU software reflash, typically adding 70–90 horsepower and 90–110 lb-ft of torque on a stock vehicle. This is a cost-effective and reversible upgrade, but it does not address the restrictive factory downpipe or the limits of the stock intercooler. Stage 2 builds on Stage 1 by adding a high-flow downpipe (or downpipes for those with RS5 Sportback models that feature a secondary cat), a revised ECU tune engineered for the lower exhaust backpressure, and often an upgraded intercooler and cold air intake as supporting modifications. It is the recommended route for owners who plan to track their RS5 or who simply demand every bit of performance the engine can deliver without upgrading the turbochargers themselves.

Detailed Kit Components

ECU Tune

The heart of the APR Stage 2 kit is the custom ECU calibration. APR engineers spend months on the dyno and in real-world testing to optimize ignition timing, air-fuel ratios, boost targets, and throttle response maps. The tune is specific to the fuel octane being used, with options for 91, 93, and even 100-octane race fuel. On 93 octane, the Stage 2 software targets approximately 24–26 psi of boost (up from about 18–20 psi stock). The software also adjusts the transmission shift points on DSG-equipped cars, ensuring the increased torque is put to the road efficiently.

High-Flow Downpipe

The factory downpipe contains a restrictive catalytic converter and a secondary catalytic converter on the RS5. Replacing it with a high-flow catted or catless downpipe reduces exhaust backpressure significantly, allowing exhaust gases to exit the turbocharger more freely. This has two major effects: it lowers exhaust gas temperatures (EGTs) under heavy load, reducing heat soak, and it enables the turbochargers to spool more quickly. APR offers a downpipe that integrates a high-flow GESI catalyst for those who must pass emissions inspections, while a catless version is available for off-road/track use only.

Cold Air Intake System

While not strictly mandatory for Stage 2 performance, an upgraded intake is highly recommended. The factory intake system is already efficient, but an aftermarket intake with a larger air filter and smoother ducting can reduce intake air temperature and improve airflow to the turbos. APR’s intake uses a carbon fiber housing and a washable high-flow filter, and it has been shown to reduce intake temperatures by up to 20 degrees Fahrenheit during sustained hard driving.

Intercooler and Heat Management

The twin-turbo 2.9-liter engine generates considerable heat, and the factory intercooler (which is a water-to-air unit mounted on top of the engine) struggles to maintain consistent charge air temperatures during repeated pulls. APR’s Stage 2 kit includes an upgraded intercooler core with increased heat exchanger surface area and an auxiliary coolant pump to increase flow. This ensures that intake air temperatures remain stable, preventing the ECU from pulling timing due to knock. The result is repeatable power, pull after pull, even on hot days or at the track.

Installation and Professional Tuning

Installing the APR Stage 2 kit is not a driveway job for most owners. The downpipe replacement in particular requires lifting the vehicle and accessing tight spaces around the exhaust manifolds. The intercooler swap involves draining the coolant system and carefully purging air after refilling. The ECU tune is uploaded via APR’s proprietary flashing tool, which connects to the OBD-II port. While the software process is relatively straightforward, the hardware installation should be performed by an experienced mechanic or an authorized APR dealer. Many shops offer a bundled installation service with the kit purchase. Expect between 6 and 10 hours of labor, depending on the complexity of the downpipe replacement.

Dyno-Verified Gains and Real-World Results

APR publishes official dyno results for its Stage 2 kit on the Audi RS5. On a 93-octane map, the typical output is 507 horsepower and 562 lb-ft of torque at the crankshaft (approximately 450–460 whp and 510–520 wtq on a Dynojet). This represents a gain of roughly 63 horsepower and 119 lb-ft of torque over the factory rating. The torque curve fills in dramatically; peak torque arrives earlier and is maintained across a broader rev range. In real-world terms, this translates to a 0–60 mph time in the mid-3-second range (depending on traction and launch control) and a quarter-mile time in the mid-11-second range at trap speeds approaching 120 mph. The improvement in mid-range punch is particularly noticeable when accelerating from 40 to 80 mph for highway passing.

Driving Impressions – More Than Just Numbers

While dyno numbers are impressive, the transformation in driving feel is equally important. After the Stage 2 upgrade, the RS5 feels lighter on its feet. The throttle becomes more responsive, with less lag off the line. The exhaust note deepens with the free-flowing downpipe, producing a more aggressive growl at full throttle while remaining civil during cruising. The car also responds better to part-throttle inputs, making it more engaging on winding roads. One area that stands out is the improved mid-range torque: you can overtake in sixth or seventh gear without needing a downshift, whereas stock would require dropping two gears. This is the hallmark of a well-calibrated Stage 2 package.

Supporting Modifications for Maximum Performance

To get the most out of the APR Stage 2 kit, a few supporting modifications are recommended. An upgraded high-pressure fuel pump (HPFP) can help maintain fuel pressure under the increased demand of the Stage 2 tune, though many cars manage fine with the stock pump on 93 octane. Spark plugs should be changed to a one-step colder range (e.g., NGK 95538) to prevent pre-ignition under high boost. A DSG transmission tune is also highly advisable; APR offers a separate TCU tune that raises shift points, increases line pressure, and reduces shift times. Without the TCU tune, the transmission may feel hesitant as it tries to adapt to the newfound torque. Additionally, many owners upgrade the engine and transmission mounts to reduce wheel hop during hard launches.

Maintenance and Reliability Considerations

With great power comes greater responsibility. A Stage 2 Audi RS5 will require more frequent maintenance. Oil change intervals should be shortened to every 3,000–5,000 miles (especially if track use is involved). The upgraded downpipe and intercooler should be inspected for leaks and debris annually. Spark plugs should be replaced every 15,000–20,000 miles, as the higher heat and pressure accelerate electrode wear. The DSG transmission fluid and filter should be serviced every 30,000 miles. Despite these increased maintenance demands, the EA839 engine is known for its strength when properly maintained. Many owners have logged tens of thousands of miles on Stage 2 tunes without major issues.

Warranty and Regulatory Considerations

Installing any Stage 2 kit will void the factory powertrain warranty if a warranty claim is made for a related failure. However, APR offers a limited warranty on its own products (typically one year from purchase). Some owners choose to revert to the stock software and downpipe before dealer visits, though a diligent technician may detect the flash through tamper-proof logs. It is important to check local emissions regulations, as a catless downpipe will fail a visual inspection in many states and countries. The catted downpipe option is legal in most areas, but it is still an aftermarket catalytic converter that may require a tune to disable the oxygen sensor readiness monitors for inspection.

Comparing APR Stage 2 to Alternative Tuning Options

APR is not the only player in the RS5 tuning space. Brands like Unitronic, Integrated Engineering (IE), and 034Motorsport offer similar Stage 2 kits. Each has its own tuning philosophy and supporting hardware. Unitronic’s tune, for example, is known for being slightly more conservative on boost but extremely smooth in daily driving. IE offers very competitive dyno numbers with a focus on maximum mid-range torque. 034Motorsport has a reputation for excellent customer support and a strong community presence. Choosing between them often comes down to personal preference, local dealer support, or familiarity with the tuning software. APR differentiates itself with a long history in VAG tuning, extensive R&D, and a robust dealer network across the globe. It is also one of the few tuners that offers CARB EO numbers for some of its products, which is a significant advantage for California owners.

Conclusion

The APR Stage 2 kit is a thoroughly engineered package that unlocks the true potential of the Audi RS5. By upgrading the downpipe, intake, and intercooler alongside a custom ECU calibration, owners can expect a verified 60+ horsepower and over 100 lb-ft of torque gain. The result is not only faster lap times and higher top speeds but a more rewarding and engaging driving experience every day. As with any performance modification, considerations around warranty, maintenance, and local regulations should be weighed carefully. For those willing to invest in the hardware and professional installation, the APR Stage 2 kit transforms the already capable RS5 into a genuine supercar contender.