Understanding the APR Downpipe for the Audi S5 3.0T

The factory downpipe on the Audi S5 3.0T is a significant bottleneck in the exhaust system. Its primary function is to direct exhaust gases from the turbocharger to the rest of the exhaust, but its restrictive design limits flow, especially when the engine is tuned for higher output. The APR Downpipe addresses this by replacing the stock piece with a larger diameter, less restrictive unit made from high-quality stainless steel. This upgrade is a critical first step for anyone aiming to push the S5’s supercharged V6 beyond stock power levels.

Key features of the APR Downpipe include:

  • High-Flow Design: The APR unit uses mandrel-bent tubing to maintain a consistent inner diameter, reducing turbulence and backpressure. This allows the turbocharger to spool more freely and improves exhaust scavenging.
  • Durable Construction: Fabricated from T304 stainless steel with CNC-machined flanges, the downpipe is built to withstand high exhaust temperatures and resist corrosion over the life of the vehicle.
  • Catalytic Converter Options: APR offers both a catted (high-flow catalyst) and a catless version. The catted option retains emissions compliance for street use, while the catless version is intended for off-road or track use and yields the maximum flow.
  • Direct Fitment: The downpipe bolts directly to the factory exhaust system and turbocharger, requiring no modifications for installation. It is designed exclusively for the Audi S5 with the 3.0T (supercharged) engine.

The Role of an Upgraded Intake System

While the downpipe improves the exit of exhaust gases, the intake system must supply sufficient cool, dense air on the front end. The APR Carbon Fiber Intake System is engineered to reduce intake restrictions and lower intake air temperatures. Factory airboxes are often designed for noise suppression and cost efficiency, which can choke high-performance engines. A free-flowing intake is essential for realizing the full potential of the downpipe and an ECU tune.

Benefits of the APR Intake include:

  • Increased Airflow: The large carbon fiber intake tube and high-flow filter element allow the engine to draw in more air with less resistance. This is measured by a reduction in intake restriction compared to the factory system.
  • Reduced Intake Air Temperatures: The carbon fiber construction helps insulate the incoming air from engine bay heat. The intake also features a sealed airbox design that draws air from the front grille rather than hot bay air.
  • Improved Throttle Response: With less restriction, the engine can react more quickly to throttle inputs. Many drivers report a seat-of-the-pants improvement in throttle responsiveness, especially when combined with a downpipe tune.
  • Enhanced Engine Sound: The intake amplifies the natural supercharger whine and adds a deeper intake note under acceleration. This injects a more aggressive character into the driving experience without being overly loud inside the cabin.

Performance Gains: How APR Downpipe & Intake Deliver 70+ HP

By themselves, the APR Downpipe and Intake provide modest gains—typically in the range of 15–25 horsepower when installed without tuning. However, the synergy of these components truly shines when combined with an ECU tune. APR’s Stage 2 calibration is specifically designed to take advantage of the increased airflow from both the downpipe and intake. The result is a verified increase of more than 70 horsepower at the wheels on a Dynojet dynamometer.

Let’s break down the power increase by component:

  • Stock Audi S5 3.0T: Approximately 330 hp (crank).
  • With APR Intake only (Stage 1): ~360–370 hp at the crank (depending on calibration).
  • With APR Downpipe + Intake (Stage 2): ~400–420 hp at the crank, which translates to roughly 350–370 whp on a Dynojet. The 70+ hp increase is measured at the wheels over a stock baseline—meaning total crank horsepower can exceed 440 hp in some cases when factoring drivetrain loss.

Beyond peak power, the torque curve is significantly improved. The Stage 2 setup provides stronger mid-range punch and maintains boost pressure longer due to reduced backpressure. Real-world data from numerous dyno runs on enthusiast forums (e.g., Audizine) consistently show gains of 70–85 whp with the APR downpipe and intake combo, making it one of the best value-for-dollar modifications for the B8/B8.5 S5.

Important Note: These gains assume you are running 93 octane fuel and have a proper tune. Without tuning, the intake and downpipe will still yield small improvements, but the full 70+ hp increase requires an ECU flash.

Total Cost Breakdown: What to Expect

The price of the APR Downpipe and Intake combo varies depending on the specific variant (catted vs. catless downpipe) and whether you purchase new or used. Below is a conservative estimate for a new setup with professional installation. Prices are in USD as of 2025.

Component Estimated Cost
APR Carbon Fiber Intake (CFI) $399 – $499
APR Downpipe (catted) $1,099 – $1,299
APR Downpipe (catless) $899 – $1,099
APR Stage 2 ECU Tune $599 – $799
Installation (shop labor, 4–6 hours) $400 – $600
Total (catted + tune + labor) ~$2,300 – $2,700
Total (catless + tune, no labor) ~$1,500 – $1,900

If you are a capable DIY mechanic, you can save on installation costs. The downpipe is the more challenging part; the intake installation is straightforward. Many owners report successfully installing both in a driveway over a weekend. However, be prepared for dealing with stubborn oxygen sensors and rusted bolts on older vehicles.

Additionally, some APR dealers offer package deals where the intake, downpipe, and tune are sold together at a discount, potentially bringing the total under $2,500 with installation. Check APR’s official website for current pricing and authorized distributor listings.

Installation Process: What to Expect

Installation of the APR Downpipe and Intake is a moderate DIY job, but it is best performed by a professional if you lack experience with exhaust work or turbo vehicles. Here is a detailed step-by-step overview of the process for the B8/B8.5 Audi S5 3.0T.

Downpipe Installation

  1. Preparation: Jack up the vehicle and secure it on jack stands. Disconnect the negative battery terminal. Allow the exhaust to cool completely.
  2. Remove protective shields: Remove the underbody engine cover and any heat shields near the downpipe area.
  3. Disconnect oxygen sensors: Unplug the primary and secondary O2 sensors. Carefully remove them from the factory downpipe using an O2 sensor socket.
  4. Unbolt the downpipe: The downpipe connects to the turbocharger outlet and the cat-back exhaust. Loosen the clamps and bolts. You may need penetrating oil if there is corrosion.
  5. Remove the factory downpipe: Maneuver the stock downpipe out from below the car. It may require some twisting to clear the subframe.
  6. Install the APR downpipe: Position the new downpipe in place. Use the supplied gasket and hardware. Tighten all bolts to APR’s specified torque (usually 30–40 ft-lbs).
  7. Reinstall oxygen sensors: Install the O2 sensors into the APR downpipe’s bungs. The secondary sensor often requires a spacer to avoid a check engine light (APR includes a mini-cat spacer with the catted downpipe).
  8. Double-check all connections: Ensure no exhaust leaks are present by starting the engine and listening for hissing sounds.

Intake Installation

  1. Remove the factory airbox: Disconnect the mass airflow sensor (MAF) plug and loosen the intake tube clamps. Lift the airbox out.
  2. Install the APR intake base: The carbon fiber lower section mounts to the factory intake mounting points. Some trimming of a plastic snow guard may be required for proper fitment.
  3. Attach the intake tube: Secure the large carbon fiber tube to the throttle body with the provided silicone coupler and T-bolt clamps.
  4. Mount the filter and cover: Install the washable high-flow air filter into the base. Place the carbon fiber lid on top and secure it with the included hardware.
  5. Reconnect the MAF sensor: Carefully plug the sensor into the new intake tube. Double-check that the seal is tight.
  6. Test operation: Start the engine and inspect for any loose clamps or unmetered air leaks. A quick test drive will confirm normal idle and throttle response.

Detailed installation guides and videos are available on the APR support site. For those new to working on modern German cars, it is highly recommended to have a professional handle the downpipe replacement, as mishandling the turbocharger flange or O2 sensors can lead to costly repairs.

Tuning: The Missing Piece to Unlock Full Power

Without an ECU tune, the APR Downpipe and Intake will only unlock about 15–30% of their potential. The factory ECU mapping does not adjust fuel, boost, or ignition timing to take advantage of the freer breathing exhaust and intake. APR’s Stage 2 tune is specifically calibrated for their downpipe and intake, and it remaps these parameters for optimal performance.

Tuning through APR is straightforward: you purchase the upgrade from an authorized dealer, who flashes the new software onto the ECU via the OBD-II port. The process takes about 30 minutes. APR also offers multiple file options (93 octane, 91 octane, and 100 octane race fuel) so you can switch between tunes. A handheld programmer (APR Mobile) is available for those who want to flash at home, though this adds to the cost.

Important considerations for tuning:

  • Warranty: APR’s tunes are designed to be reversible. You can flash back to stock before dealer visits, though the ECU may still be flagged as “tampered” if the dealer checks flash counts. APR does offer a limited manufacturer’s warranty on their tune itself, but it does not cover powertrain failures caused by tuning. Always consider the risk when modifying your vehicle.
  • Fuel Quality: The Stage 2 tune requires at minimum 91 octane fuel (93 recommended). Using lower octane can cause knock and reduce power. APR’s software includes knock detection, but consistent use of poor fuel can damage the engine.
  • DPF/Emissions: Catless downpipes will trigger a check engine light for catalyst inefficiency unless the tune disables the rear O2 sensor monitoring. APR’s Stage 2 tune does include this disable for catless applications, making it a clean install without a spacer.

Additional Considerations: Sound, Reliability, and Emissions

Sound

The combination of a downpipe and intake dramatically changes the Audi S5’s auditory signature. The intake adds a pronounced supercharger whine, especially under part throttle. The downpipe deepens the exhaust note and adds more volume. With a full cat-back system, the sound can become quite aggressive. Those seeking a subtle daily driver might prefer the catted downpipe to keep volume in check. The catless option is noticeably louder and has a raw, race-car quality on cold starts.

Reliability

APR is a well-established aftermarket manufacturer with a reputation for reliability when properly installed. The downpipe and intake do not stress the turbocharger beyond its designed limits, as the Stage 2 tune keeps boost within safe parameters. However, any modification that increases power will increase wear on components like the clutch (DSG) or torque converter (automatic) over time. The 3.0T supercharger is robust, and many Stage 2 cars have logged tens of thousands of miles without issues.

Emissions

In many regions, modifying the emissions equipment (catalytic converter) is illegal for street use. The catless downpipe removes the primary catalytic converter entirely, making the vehicle fail visual emissions inspections. The catted downpipe retains a high-flow catalyst that is usually sufficient to pass tailpipe emissions tests, but it may still fail visual checks in strict jurisdictions (like California). Know your local laws before purchasing a downpipe.

Conclusion: Is the APR Downpipe & Intake Combo Worth It?

For Audi S5 3.0T owners serious about extracting real, measurable horsepower gains, the APR Downpipe and Intake combo delivers exactly what it promises: a verified increase of 70+ horsepower when paired with a Stage 2 tune. The total cost of approximately $2,400 (including parts and professional installation) is competitive compared to other power mods like supercharger pulleys or aftercoolers, and the installation is relatively straightforward for a skilled shadetree mechanic. The benefits aren’t just numbers on a dyno sheet—the improved throttle response, more aggressive exhaust note, and sharper sound from the intake transform the daily driving experience. If you are ready for the next step beyond a basic tune, this package is a proven, reliable upgrade that has cemented its place as a staple in the 3.0T aftermarket.

For more information, visit APR’s official product pages and check community discussions on forums like Audizine for real owner feedback and dyno charts.