Understanding the Skunk2 Intake Manifold for the RSX Type S

The Skunk2 Pro Series intake manifold is one of the most popular performance upgrades for the K20A2 engine found in the RSX Type S. Unlike the factory manifold, which prioritizes low-end torque and emissions compliance, the Skunk2 design focuses on high-rpm airflow and volumetric efficiency. The manifold features larger-diameter runners (typically 70mm compared to the stock 62mm) and a larger plenum volume, allowing the engine to breathe more freely above 4000 RPM. This design reduces intake restriction and helps the engine produce peak horsepower numbers that are difficult to achieve with the stock manifold alone.

The Skunk2 manifold is made from a lightweight cast aluminum alloy, which reduces weight over the stock unit while offering better heat dissipation. The runner length and plenum shape have been optimized for the K-series head’s intake port geometry, making it a direct bolt-on upgrade. However, because the manifold changes the airflow characteristics significantly, it works best when paired with other supporting modifications like a cold-air intake, aftermarket header, and a proper engine tune.

Measurable Power Gains on the RSX Type S

Dyno tests on stock or lightly modified RSX Type S vehicles show that the Skunk2 intake manifold can deliver 10–15 horsepower and similar torque gains at the wheels when combined with a tune. The increase is most noticeable in the mid-to-upper RPM range, where the stock manifold starts to restrict airflow. The manifold’s larger plenum volume helps maintain intake velocity even at higher engine speeds, reducing the typical torque dip that K20 engines experience around 5500 RPM.

With supporting mods—such as a cold-air intake, 70mm throttle body, and a tuned ECU—gains can exceed 20 horsepower. Many enthusiasts also report improved throttle response and a smoother power delivery across the entire rev range after installation. However, it’s important to note that without ECU recalibration, the engine may run lean at higher RPMs, potentially causing knock or reduced performance. Always budget for a professional dyno tune or a quality flash tune when installing a Skunk2 intake manifold.

Typical Dyno Results

  • Stock RSX Type S (2002–2004): ~200 hp at the crank. With Skunk2 manifold + tune: 210–215 hp at the crank.
  • RSX Type S with bolt-ons (intake, header, exhaust): ~210–220 whp. Adding Skunk2 manifold + tune: 225–235 whp.
  • RSX Type S with full bolt-ons, cams, and manifold: ~240–250 whp (requires additional engine work).

Installation Tips for a Successful Upgrade

Installing a Skunk2 intake manifold on a K20A2 requires moderate mechanical skill but can be completed in a home garage with the right tools. Below is a detailed step-by-step guide covering preparation, removal, installation, and post-install checks.

Tools and Parts You Will Need

  • Socket set with 10mm, 12mm, 14mm sockets (both short and deep)
  • Torque wrench (capable of 15–22 ft-lbs for manifold bolts)
  • Gasket scraper or razor blade
  • New intake manifold gasket (OEM or Skunk2 included)
  • Throttle body cleaner and rags
  • Blue thread-locker (Loctite 242 for manifold bolts)
  • Vacuum caps (if deleting unused ports)
  • New coolant hose clamps (for upper radiator hose if moved)

Optional: carbon fiber or thermal intake manifold gasket to reduce heat soak.

Step 1 – Remove the Stock Intake Manifold

  1. Disconnect the negative battery terminal and wait 5 minutes for the ECU to discharge capacitors.
  2. Remove the entire factory air intake system (air box, intake tube, MAF sensor) to access the throttle body.
  3. Label and unplug all electrical connections from the intake manifold: throttle position sensor, idle air control valve, manifold absolute pressure (MAP) sensor, and any EGR/emissions connectors.
  4. Detach the throttle cable from the throttle body bracket. (On RSX Type S, the cable is housed in a plastic sleeve; gently pop out the clip.)
  5. Disconnect the two coolant hoses that run to the throttle body – be prepared for some coolant spillage.
  6. Remove the vacuum lines attached to the stock manifold – note which lines connect to the intake port on the valve cover, the fuel pressure regulator, and the EVAP system.
  7. Unbolt the six 12mm bolts securing the intake manifold to the cylinder head. A 12mm deep socket with an extension works best.
  8. Carefully wiggle the stock manifold out of the engine bay. The manifold may get caught on the fuel rail; you can remove the fuel rail (four 10mm bolts) for easier removal.

Tip: Clean the mating surface on the cylinder head with a gasket scraper and brake cleaner. Ensure no old gasket material remains to prevent vacuum leaks.

Step 2 – Prepare the Skunk2 Manifold

  • Place the new Skunk2 manifold on a clean workbench. Inspect all vacuum ports – the Skunk2 manifold typically has fewer ports than stock. You may need to cap unused vacuum ports with rubber caps or install a vacuum manifold block.
  • If you are reusing your original throttle body, thoroughly clean it with throttle body cleaner and a soft brush. Reinstall the throttle body onto the Skunk2 manifold using a new gasket (included with many Skunk2 units). Torque the four throttle body bolts to 10 ft-lbs.
  • Transfer the stock fuel rail and injectors (or aftermarket injectors) to the new manifold. The Skunk2 manifold uses the same injector clip pattern; ensure the O-rings are properly lubricated with fuel-resistant grease.
  • Apply blue thread-locker to the six manifold mounting studs (if using studs) or to the bolts.

Step 3 – Install the Skunk2 Manifold

  1. Place the new intake manifold gasket onto the cylinder head studs. OEM-style gaskets are fine; some aftermarket gaskets require careful alignment of the two locating pins.
  2. Position the Skunk2 manifold onto the studs. It will be a tight fit – you may need to tilt the manifold upward to clear the water outlet. Do not force it; gently rock the manifold while aligning the fuel rail with the injectors.
  3. Hand-thread all six manifold bolts, then torque them to 16 ft-lbs in a crisscross pattern. Do not overtighten, as the aluminum threads in the head can strip.
  4. Reconnect the throttle cable. Adjust the cable tension so there is minimal slack – the throttle should snap closed when released.
  5. Reattach all electrical connectors: TPS, IACV, MAP sensor. Ensure the wiring harness is routed away from hot surfaces.
  6. Reconnect vacuum lines. The Skunk2 manifold often relocates the vacuum source for the brake booster; you may need a longer piece of 3/8″ vacuum hose.
  7. Fill the coolant system if you removed any hoses. Use only Honda type-2 or compatible coolant.
  8. Reinstall the cold-air intake system. If you are using a short ram, check that the intake tube clears the brake master cylinder.

Important: The Skunk2 manifold sits slightly differently than stock. You may need to adjust or reroute the upper radiator hose, as the manifold can contact it. Use a heat-resistant silicone hose or bend the metal tube slightly to prevent rubbing.

Step 4 – Final Checks and First Start

  • Double-check all bolts, clamps, and electrical connections.
  • Reconnect the battery negative terminal.
  • Prime the fuel system by turning the ignition to “ON” for 3 seconds, then off, then on again (repeat 2-3 times).
  • Start the engine. It may idle high and rough for a few seconds while the ECU relearns.
  • Listen for vacuum leaks: a hissing sound indicates an unplugged port or loose gasket. Spray a small amount of carburetor cleaner around the manifold gasket – if idle changes, you have a leak.
  • Check for coolant leaks at the throttle body hoses.
  • Perform a throttle response test: rev the engine to 3000 RPM and release – the RPM should drop smoothly without hunting.

Note: After the first drive, return home and check the manifold bolt torque again, as the gasket may compress slightly.

Tuning and Calibration Requirements

Installing a Skunk2 intake manifold without recalibrating the ECU can lead to poor drivability, rough idle, and potential engine damage. The increased airflow changes the volumetric efficiency of the engine, which the stock ECU cannot compensate for beyond its narrow fuel trim limits. At minimum, use a quality flash tune (like Hondata FlashPro) with a base map designed for the Skunk2 manifold. A professional dyno tune is highly recommended to optimize ignition timing and air/fuel ratios across the entire RPM range.

Tuning will also allow you to disable any unnecessary emissions hardware (like the secondary air injection system) if you have removed it. The shop can also calibrate the idle air control valve to handle the larger plenum volume, preventing stalling when coming to a stop.

Common Issues and Troubleshooting

  • Vacuum leaks: The most common post-install issue. Use a smoke tester or propane torch method to locate leaks. Tighten bolts or replace gasket as needed.
  • Hard starts / rough idle: Often caused by unmetered air from an improper MAF sensor placement or a missing vacuum cap. Verify that the intake uses a blow-through MAF configuration if applicable.
  • Coolant hose interference: The upper radiator hose may contact the manifold. A silicone hose with a 45° bend can solve this.
  • Brake booster vacuum: The Skunk2 manifold does not include a dedicated brake booster port. You must tap the plenum or use a vacuum distribution block. Failure to connect the booster will result in a rock-hard brake pedal.
  • Throttle body alignment: Some Skunk2 manifolds require a spacer or drilling new holes for the throttle body. Check the compatibility of your specific unit (e.g., Pro Series vs. Ultra Series).

External Resources

Conclusion

The Skunk2 intake manifold is a proven upgrade for the RSX Type S K20A2 engine, delivering measurable gains in horsepower and throttle response when properly installed and tuned. While the installation is straightforward for experienced DIYers, attention to detail—especially regarding vacuum lines, coolant routing, and gasket sealing—is critical for a reliable result. Pair the manifold with a quality intake, header, and ECU calibration to unlock the full potential of your K20. With these tips, your RSX Type S will be ready to breathe freely and perform at its best on both street and track.