Upgrading the throttle body is one of the most straightforward ways to improve airflow and throttle response on a turbocharged Subaru WRX. The CTS Turbo Throttle Body Upgrade has gained a strong following among WRX owners looking for a noticeable bump in performance without the complexity of a full turbo or intercooler swap. This article covers the real-world horsepower gains, the engineering behind the improvement, a detailed step-by-step installation guide, and everything you need to know to complete the upgrade yourself.

Why Upgrade the Throttle Body on a Subaru WRX?

The factory throttle body on the Subaru WRX is designed for a balance of cost, durability, and emissions compliance. While it works well for stock power levels, it creates a measurable restriction once you start modifying the intake, turbo, or exhaust. The stock bore diameter is typically 60mm or 62mm depending on the model year, which limits the volume of air that can enter the intake manifold under high boost.

By increasing the throttle body bore to 68mm or 70mm (as in the CTS Turbo offering), you reduce the pressure drop across the throttle plate. This allows the turbo to push more air into the engine with less effort, resulting in improved cylinder filling and a more efficient combustion cycle. The net effect is a gain of up to 10 wheel horsepower on a mostly stock WRX, with even larger gains on vehicles with supporting modifications like a cold air intake, downpipe, and a tune.

Power Gains: What to Expect

CTS Turbo claims up to 10 horsepower from their throttle body upgrade on a stock WRX. Independent dyno testing on the FA20 and EJ series engines confirms that most cars see between 6 and 10 whp, with a peak torque increase of 5–8 lb-ft. The gains are not just peak numbers; the entire powerband benefits from improved throttle response and mid-range torque. This is especially noticeable during partial throttle acceleration and when transitioning from a closed to open throttle, such as when exiting a corner or merging onto a highway.

For owners running a Stage 2 setup (intake, downpipe, and tune), the CTS throttle body can add an extra 10–15 horsepower and sharpen the response even further. It complements other bolt-on modifications by reducing a bottleneck that often goes overlooked.

Key Benefits of the CTS Turbo Throttle Body

  • Increased horsepower and torque: Up to 10 whp on stock cars, more on modified ones.
  • Throttle response improvement: The larger bore and smoother airflow path reduce lag when you stab the gas.
  • Better airflow at all RPM: Less restriction means the turbo doesn’t have to work as hard to flow the same amount of air.
  • Direct bolt-on design: Uses the same bolt pattern and gasket as the stock unit, so no adapter plates are needed.
  • Durable construction: Billet aluminum body with a corrosion-resistant finish, designed to handle high-temperature underhood conditions.

Tools and Materials Required

Before you begin, gather the following tools to avoid interrupting the install to run to the hardware store:

  • 10mm, 12mm, and 14mm sockets with a ratchet and extension
  • Torque wrench capable of 15–20 ft-lbs (for throttle body bolts)
  • Flathead screwdriver (to release hose clamps)
  • Phillips screwdriver (if your WRX uses screw-type clamps)
  • Shop towels or clean rags
  • Throttle body gasket (CTS Turbo includes a new one, but have a spare just in case)
  • Safety glasses and gloves
  • A small brush or compressed air to clean the intake manifold sealing surface
  • Optional: Isopropyl alcohol or brake cleaner for degreasing the mounting surface

Installation Step-by-Step Guide

1. Safety and Preparation

Make sure the engine is completely cool to avoid burns. Park the car on a level surface and disconnect the negative battery terminal. This prevents any accidental short circuits and resets the ECU’s learned idle values, which is helpful for the throttle body relearn later.

2. Remove the Intake Duct and Air Box

To access the throttle body, you need to clear the intake pathway. Remove the intake duct from the air filter box to the turbo inlet, then unbolt the air box assembly. On later WRX models, you may also need to disconnect the mass airflow sensor connector before lifting the duct out. Keep the fasteners in a labeled bag or magnetic tray.

3. Disconnect the Throttle Body Components

Locate the throttle body attached to the front of the intake manifold. You’ll see two coolant hoses, a vacuum line, and the electrical connector for the throttle position sensor and idle air control (if present). On drive-by-wire systems (2008+ WRX), the electrical connector is the only wire. Carefully pull the connector straight out — do not pry on the plastic. Use a flathead screwdriver to release the spring clips on the coolant hose clamps. Have a rag ready because a small amount of coolant will spill.

4. Remove the Stock Throttle Body

Using a 12mm or 14mm socket, remove the four bolts holding the throttle body to the intake manifold. Often these bolts are tight, so use a breaker bar if needed. Once all bolts are out, gently rock the throttle body to break the gasket seal. Lift it off and set it aside on a clean surface. Immediately cover the intake manifold opening with a clean rag to prevent debris from entering the engine.

5. Clean the Mounting Surface

Use a plastic scraper or a rag soaked in brake cleaner to remove any old gasket material from the intake manifold flange. Be thorough — any leftover bits can cause vacuum leaks. The surface should be smooth and dry before installation.

6. Prepare the CTS Turbo Throttle Body

Unbox the CTS unit. It comes with a new gasket. Verify that the gasket matches the bolt pattern and that the throttle plate moves freely. Apply a light film of engine oil to the throttle blade pivot points (not the bore). Do not lubricate the bore itself — the air path should remain clean.

7. Install the New Throttle Body

Position the new gasket on the intake manifold studs or align it by hand. Place the CTS throttle body onto the gasket. Insert the four bolts and hand-tighten them in a cross pattern (top-left, bottom-right, top-right, bottom-left). Use a torque wrench to tighten to the manufacturer’s specification — typically 15–20 ft-lbs for aluminum intake manifolds. Over-tightening can strip threads or warp the flange.

8. Reconnect the Hoses and Electrical Connectors

Reattach the coolant hoses: push them onto the barbs and secure the clamps. Reconnect the vacuum line. Plug in the electrical connector until you hear a distinct click. Double-check that the connector is fully seated.

9. Reinstall the Intake Duct and Air Box

Reverse the steps from earlier. Reinstall the air box, ensuring the air filter is clean and properly seated. Reconnect the MAF sensor connector. Reattach any other hoses or wiring you moved during disassembly.

10. Reconnect the Battery and Perform Idle Relearn

Reconnect the negative battery terminal. Turn the ignition to the ON position (do not start) for 10 seconds, then turn it OFF for 10 seconds. Start the engine and let it idle for 5–10 minutes without touching the throttle. This allows the ECU to relearn the idle air control range. Some WRX models require a brief test drive to complete the idle reset — drive gently for the first 10 miles, varying RPM but avoiding full throttle.

Post-Installation Checks and Common Issues

After installation, check for any coolant or air leaks. Feel around the throttle body gasket area for any whistling sounds, which indicate a vacuum leak. If you have a boost leak tester, pressurize the intake system to 10–15 psi and listen for hissing. A common oversight is not tightening the hose clamps enough — coolant can weep and cause a slow loss.

If the check engine light comes on, it is usually due to a disconnected sensor, a vacuum leak, or the ECU needing to complete a drive cycle. Scan the code with an OBD-II reader. Most throttle body upgrades do not require tuning on a stock WRX, but for maximum performance and to avoid an overly lean condition at wide-open throttle, a professional ECU tune is highly recommended. Even a conservative tune will safely unlock the full potential of the increased airflow.

Tuning Considerations

The CTS Turbo throttle body flows more air, which changes the mass airflow sensor readings. On a stock ECU, the fuel trims will adapt to a point, but at higher boost levels the engine may run slightly lean. A custom tune (via Accessport or open-source tools like RomRaider) can dial in the fuel and ignition timing to match the new flow. Many owners combine this throttle body with a Cobb Accessport and a Stage 1 or Stage 2 map from a reputable tuner. The result is a smooth, responsive powerband with strong mid-range punch.

Cost vs. Performance Value

At around $250–$350, the CTS Turbo throttle body is one of the most cost-effective bolt-on upgrades for a WRX. It delivers a clear improvement in drivability without the installation complexity of a turbo swap or intercooler upgrade. When combined with a quality intake and a tune, the throttle body helps the engine breathe more freely, making all your other modifications work harder. For drivers looking for a tangible everyday improvement, this is a smart investment.

Frequently Asked Questions

Will the CTS Turbo throttle body fit all Subaru WRX models?

CTS Turbo offers versions for both the EJ-series engines (2002–2014 WRX/STI) and the FA20 engine (2015+ WRX). Always verify the part number for your specific model year.

Do I need a tune after installing the throttle body?

Not strictly required, but strongly recommended. The ECU can self-adjust to an extent, but a tune ensures you gain the full horsepower and avoid any lean conditions.

Can I install this throttle body without removing the intercooler?

On most WRX models, the intercooler does not need to be removed unless you have very large aftermarket piping. You only need to take off the intake duct and air box.

What is the expected lifespan of the CTS Turbo throttle body?

The billet aluminum body is highly durable. The internal components — throttle shaft, bearings, and plate — are designed to outlast the car with proper maintenance. No periodic servicing is needed beyond normal intake cleaning.

Final Thoughts

The CTS Turbo Throttle Body Upgrade is a proven, low-risk modification that delivers measurable gains in horsepower and throttle response. For the DIY enthusiast, the installation is straightforward and can be completed in about an hour with basic hand tools. Paired with a tune and other bolt-ons, it unlocks the WRX’s true potential. Whether you’re building a daily driver or a track-day weapon, this upgrade is a solid step toward building a more responsive, powerful Subaru.

For more detailed install guides and owner experiences, check out IWSTI.com and the NASIOC forums where thousands of WRX owners share firsthand knowledge.