Introduction: Unlocking the True Potential of Your A90 Supra

The Toyota Supra A90, equipped with the BMW B58 engine, is a formidable platform right out of the factory. However, enthusiasts quickly discover that the stock downpipe is one of the most restrictive components in the exhaust system. The ARK Performance A90 Supra downpipe is engineered to eliminate this bottleneck, allowing exhaust gases to flow more freely from the turbocharger. This single modification can yield significant gains in horsepower and torque, improve throttle response, and enhance the iconic exhaust note of the inline-six engine. Whether you are preparing for stage 2 tuning or simply seeking a more spirited driving experience, installing an aftermarket downpipe is a rewarding and relatively straightforward project for the home mechanic. This guide provides a comprehensive, step-by-step walkthrough for the entire installation process, from gathering the right tools to performing the final test drive.

Benefits of Upgrading to an ARK Performance Downpipe

Before diving into the installation, it is important to understand why this upgrade is so popular among Supra owners. The ARK Performance downpipe is a direct-fit replacement that offers several key advantages over the factory unit:

  • Increased Horsepower and Torque: The larger diameter and smoother mandrel-bent piping reduce exhaust backpressure, allowing the turbo to spool faster and produce more power. Gains of 20-40 wheel horsepower are common without any other modifications.
  • Improved Turbo Response: With less restriction, the turbocharger reaches boost pressure sooner, resulting in quicker throttle response and reduced lag.
  • Enhanced Exhaust Sound: The downpipe dramatically changes the character of the exhaust, giving it a deeper, more aggressive tone without being overly loud or drone-prone when paired with a quality cat-back system.
  • High-Quality Construction: ARK Performance uses 304 stainless steel with precision TIG welding, ensuring long-lasting durability and a perfect fit.
  • Optimized Catalytic Converter Option: ARK offers both catted and catless versions. The catted variant uses a high-flow GESi catalyst that reduces emissions while still outperforming the stock unit, making it a more street-friendly choice.

For those planning further modifications, the downpipe is a critical step toward achieving stage 2 or stage 3 power levels. Many tuning platforms, such as BootMod3 or MHD, include specific maps that require an upgraded downpipe to deliver safe and reliable performance gains.

Tools and Materials Required

Proper preparation ensures a smooth installation. Having all necessary tools and supplies on hand before you begin will prevent frustrating delays. Below is a comprehensive list:

Essential Tools

  • Socket set (metric): 10mm, 12mm, 13mm, 14mm, 15mm, 18mm sockets
  • Torque wrench capable of measuring in ft-lbs (range 15–80 ft-lbs recommended)
  • Ratchet with extensions (3-inch, 6-inch, and a flexible extension or wobble joint)
  • Jack and two jack stands (minimum 3-ton capacity)
  • Safety goggles and mechanic gloves
  • Flathead screwdriver or trim removal tool (for disconnecting O2 sensor clips)
  • O2 sensor socket (22mm) or a long 22mm wrench
  • Penetrating oil (e.g., WD-40 Specialist, PB Blaster)

Supplies

  • New OEM-quality exhaust gaskets (typically two: one at the turbo flange, one at the midpipe connection)
  • Anti-seize compound (copper-based or nickel-based for high-temp applications)
  • New bolts/nuts if not included with the downpipe (M10 x 1.25 flanged nuts recommended for turbo flange)
  • Shop rags or paper towels
  • Hearing protection (if working in a tight space near the exhaust)
  • Flashlight or work light
  • Phone or camera for reference photos before disassembly
  • Breaker bar (for stubborn bolts)

Note: The ARK Performance A90 Supra downpipe package typically includes the downpipe itself, a pair of O2 sensor bungs, and mounting hardware. Check the contents against the product listing to ensure nothing is missing.

Preparation: Setting Up for Success

Before lifting the vehicle, take a few minutes to prepare your workspace and the car. This reduces risk and makes the job easier.

Safety First

Always work on a level surface. If using a concrete driveway, check for slopes. Disconnect the negative battery terminal to prevent accidental airbag deployment or electrical shorts while working near sensors. Allow the engine and exhaust system to completely cool if the car has been driven recently – hot exhaust components can cause severe burns.

Lifting the Vehicle

Locate the front central jacking point on the Supra's front subframe. Place the jack under this point and raise the front of the car. Position jack stands under the designated lift points (the reinforced pinch welds just behind the front wheels). Lower the car onto the stands and verify it is stable before proceeding. You need enough clearance to work comfortably underneath – about 18-20 inches of ground clearance is ideal.

Accessing the Work Area

On the A90 Supra, the downpipe is located directly after the turbocharger, on the right (passenger) side of the engine bay. It connects to the turbo outlet and runs down to the exhaust system's midpipe. Removing the factory under-engine cover (if equipped) will provide better access from underneath. Use a 10mm socket to remove the plastic fasteners and set the cover aside.

Removing the Stock Downpipe

Removing the factory downpipe is the most challenging part of the job due to limited space and the likelihood of corroded fasteners. Work patiently to avoid stripping bolts or breaking studs.

Step 1: Disconnect the O2 Sensors

The stock downpipe has two oxygen sensors: one upstream (before the turbo) and one downstream (after the catalyst). Begin by unplugging the electrical connectors. Follow the wiring from the sensors to the clip points on the vehicle body – use a flathead screwdriver to gently release the clips. Remove the sensors themselves using an O2 sensor socket and a ratchet with an extension. Apply penetrating oil to the threads an hour before starting if they seem tight. Place the sensors aside in a clean location, labeling them if necessary to avoid confusion during reinstallation.

Step 2: Remove Heat Shields

Several heat shields surround the downpipe to protect nearby components. Using a 10mm or 12mm socket, remove the bolts securing the heat shield that covers the downpipe’s turbo flange area. Also remove the smaller shield attached to the engine block near the wastegate actuator. Keep all fasteners organized – some may be reused.

Step 3: Unbolt the Downpipe from the Turbo

Access the turbo-to-downpipe connection – four 15mm nuts secure the flange. Due to the tight space, a combination of a ratchet, extensions, and a wobble joint will be needed. Apply penetrating oil and allow it to soak for a few minutes. Use a breaker bar if the nuts are stubborn. Remove all four nuts. Note: the studs are fixed in the turbo housing; they should remain in place. If a stud unscrews with the nut, do not panic – you can reinstall it later using threadlocker, but it is best to avoid that.

Step 4: Unbolt the Downpipe from the Midpipe

Move under the car and locate the connection between the downpipe and the rest of the exhaust system. This is typically a V-band clamp or a flanged connection with two 14mm nuts (depending on the year). For the V-band, loosen the clamp nut completely. For flanged connections, remove the bolts. Support the midpipe temporarily with a jack if needed to prevent it from sagging.

Step 5: Remove the Downpipe

With all fasteners removed, the stock downpipe can be wiggled free. Lower it carefully, maneuvering around the subframe and steering rack. It may be necessary to rotate the downpipe to clear the chassis. Once out, inspect the turbo flange for any remnants of the old gasket. Clean the sealing surfaces with a rag.

Installing the ARK Performance Downpipe

Now the fun begins. The ARK downpipe is designed for a direct fit, but attention to detail during installation ensures leaks are avoided and all hardware remains secure.

Step 1: Prepare the New Downpipe

Before lifting the new downpipe into place, apply a thin layer of anti-seize to each O2 sensor bung (the threaded holes on the downpipe). This prevents the sensors from seizing later. Optionally, wrap the downpipe with exhaust heat wrap if desired, though ARK's stainless steel design typically does not require it.

Step 2: Install New Gaskets

Place a new OEM-quality gasket on the turbo outlet studs. Ensure it is aligned correctly. ARK typically includes a gasket with the downpipe, but using an OEM unit is recommended for the best seal. Also install a new gasket on the midpipe flange connection if applicable.

Step 3: Position and Secure the Downpipe

Carefully lift the ARK downpipe into position from underneath. Align the flange with the turbo studs, and slide the downpipe onto the studs. It should fit snugly. On the midpipe side, loosely install the V-band clamp or two bolts – do not tighten yet. This allows some movement for final alignment.

Step 4: Torque the Turbo Flange Nuts

Using new flanged nuts (or the ones provided), start threading them onto the studs by hand to avoid cross-threading. Tighten in a star pattern to ensure even clamping. Use a torque wrench set to 25-30 ft-lbs (check ARK’s instructions – typical spec is 26 ft-lbs). Over-tightening can warp the flange or damage the gasket.

Step 5: Tighten the Midpipe Connection

Now tighten the V-band clamp or the flange bolts. For a V-band, torque to 40-50 in-lbs (3-4 ft-lbs) – this is a low torque, just enough to cinch the clamp without deforming it. For bolted flange, use 30-35 ft-lbs.

Step 6: Reconnect O2 Sensors

Screw the upstream and downstream O2 sensors into the bungs on the new downpipe. Apply a small amount of anti-seize to the sensor threads (avoid getting it on the sensor tip). Torque to 25 ft-lbs using the O2 sensor socket. Reconnect the electrical connectors and secure the wiring to the OEM clips. Ensure wires are away from moving parts and hot surfaces.

Step 7: Reinstall Heat Shields

Refit the heat shields in the reverse order of removal. Use the original fasteners. If any bolts are corroded, replace them with stainless steel equivalents. Double-check that no tools or rags are left in the engine bay.

Post-Installation Checks and Final Steps

After everything is bolted back together, follow these steps to ensure a safe and leak-free installation.

Reconnect the Battery

Attach the negative terminal. Start the engine and let it idle for a few minutes. Listen for any unusual exhaust sounds such as hissing, which indicates a leak at one of the flanges. Feel around the connections with your hand (carefully – the downpipe will get hot quickly) to check for escaping exhaust gas. If a leak is detected, tighten the flange nuts or clamp slightly. If the leak persists, the gasket may have shifted – reinstall it.

Check for Check Engine Light (CEL)

If you installed a catted ARK downpipe, the CEL should not illuminate under normal driving. However, some vehicles may trigger a catalyst efficiency code (P0420) after long highway drives. A catless downpipe will almost certainly throw a CEL unless you have a tune that disables the rear O2 sensor. Plan to have the vehicle tuned or use an O2 sensor spacer to minimize this risk.

Test Drive and Torque Recheck

Take the Supra for a 10-minute test drive, including both city and highway conditions. Listen for any rattles or vibrations. After the test drive, park the car on a cool surface and allow the exhaust to cool for 30 minutes. Then re-torque the turbo flange nuts and the midpipe connection – thermal cycling can loosen fasteners. This step is critical for long-term reliability.

Tuning Considerations

While the car is drivable immediately, the full benefits of the downpipe are realized with an ECU tune. The stock ECU may not adjust fuel and timing enough to take advantage of the increased flow. A stage 2 tune from reputable platforms like BootMod3 or MHD will unlock the true horsepower potential and correct any CEL issues. Always use a tune designed for your specific downpipe type (catted or catless).

Common Challenges and Troubleshooting

Even with careful preparation, you may encounter a few hiccups. Here are solutions to the most frequent issues:

Stuck O2 Sensors

If the O2 sensor refuses to loosen, apply penetrating oil and use a proper O2 sensor socket. Avoid using a regular wrench, as it can round the sensor's hex. If the sensor is seized beyond removal, consider cutting the downstream sensor's wiring and using a spark plug non-foulers as a substitute, but this is a temporary fix – replace the sensor.

Turbo Studs Unscrewing

If a stud comes out with the nut, do not reuse it immediately. Clean the threads, apply red threadlocker (Loctite 272), and reinstall the stud into the turbo housing. Torque to 10-12 ft-lbs, then allow it to cure for at least an hour before installing the nut.

Exhaust Leak at Turbo Flange

A persistent leak usually indicates a warped flange or a misaligned gasket. Check that the downpipe flange is flat – ARK units are precision-machined, but shipping damage can occur. If the gasket is crushed unevenly, replace it with a new OEM one. Torquing in the correct sequence (star pattern) is essential.

Check Engine Light (Code P0420)

This is common with aftermarket downpipes. For catless pipes, tuning is the only permanent solution. For catted pipes, an O2 sensor spacer (also called a “mini-cat”) can help delay the code, but many Supra owners still eventually need a tune. A cheaper alternative is to use a right-angle O2 sensor spacer to move the sensor slightly out of the exhaust stream.

Performance Gains and Real-World Results

After a successful installation and proper tuning, the results are impressive. Independent dyno tests show that pairing the ARK Performance downpipe with a stage 2 tune can increase wheel horsepower by 60-80 hp over stock. Even on a stock tune, the boost response improves notably. The exhaust note becomes deeper and more aggressive, with a characteristic “turbo whistle” at partial throttle that many enthusiasts love. If you eventually add an intake and intercooler, the downpipe lays the foundation for a reliable 500+ wheel horsepower daily driver.

For a detailed comparison between the ARK downpipe and other brands, check out this community review thread on SupraMKV.com where owners share their experiences and dyno graphs.

Conclusion

Installing the ARK Performance A90 Supra downpipe is one of the most effective modifications you can make to improve both power and sound. By following this detailed step-by-step guide, you can complete the installation in your own garage with confidence. Remember to take your time, use the correct tools, and always prioritize safety. If at any point you feel uncomfortable working on your exhaust system, do not hesitate to consult a professional shop. The performance payoff is well worth the effort – your Supra will feel alive in a way the stock setup never could. Enjoy the build, and drive safely.