Upgrading the intake manifold on your Honda D-series engine is one of the most effective bolt-on modifications for improving airflow and throttle response. The Skunk2 intake manifold, designed specifically for the D15 and D16 platforms, offers a noticeable increase in horsepower and torque across the rev range. This comprehensive guide covers every step of the installation process, from preparation to final startup, and includes a realistic cost breakdown so you can plan your budget. Whether you are a seasoned DIY mechanic or tackling your first manifold swap, these instructions will help you get the job done right.

Tools and Materials Required

Before you begin, gather the following tools and supplies. Having everything on hand will prevent delays and ensure a smooth installation.

Essential Tools

  • Skunk2 intake manifold kit (manifold, gasket, and hardware included)
  • 3/8-inch drive socket set (10mm, 12mm, 14mm, 17mm) with extensions
  • Torque wrench (capable of 10–30 ft-lbs)
  • Flathead and Phillips screwdrivers
  • Needle-nose pliers for hose clamp removal
  • Razor blade scraper and brake cleaner for surface prep
  • Shop towels and engine degreaser
  • Vacuum cleaner or compressed air for debris removal
  • Coolant drain pan (if you need to remove coolant hoses)
  • Fuel line disconnect tool (for OBD1 D-series with quick‑connect fittings)

Consumables and Optional Items

  • High‑temperature gasket maker (e.g., Permatex Ultra Grey)
  • New coolant (if draining)
  • New throttle body gasket (recommended when reusing OEM throttle body)
  • Dielectric grease for electrical connectors
  • Threadlocker (blue) for manifold bolts

Preparation and Safety

Park the vehicle on a level surface and allow the engine to cool completely. Disconnect the negative battery terminal to prevent accidental short circuits. If your D-series engine has a coolant hose routing through the intake manifold (common on many models), drain the radiator into a clean container so you can reuse the coolant later. Label all vacuum lines, electrical connectors, and hoses with tape or zip‑ties as you remove them — this will save significant time during reassembly. The entire installation typically takes 3 to 5 hours for a first‑time installer.

Removing the Factory Intake Manifold

This is the most time‑consuming part of the job. Patience and careful organization are key.

Step 1: Remove the Air Intake System

Loosen the clamps on the air intake tube and disconnect the mass airflow sensor (if applicable) or any resonator boxes. On most D‑series engines, you will also need to remove the battery and battery tray to gain access to the lower manifold bolts. Set the intake tube aside.

Step 2: Disconnect Throttle Body and Sensors

Unplug the throttle position sensor (TPS) and idle air control valve (IACV) connectors. Remove the throttle cable from the throttle body bracket. Disconnect the vacuum lines running to the fuel pressure regulator, brake booster, and evaporative emissions system. If your car has a cruise control actuator, unbolt it and move it out of the way without disconnecting its cable.

Step 3: Remove the Fuel Rail and Injectors

The D‑series fuel rail is bolted directly to the intake manifold. Relieve fuel system pressure by disabling the fuel pump (pull the fuel pump relay or fuse) and cranking the engine once. Disconnect the fuel line using the appropriate tool — for OBD1 cars this is often a simple push‑type connector. Remove the fuel rail bolts and carefully lift the rail with the injectors attached. Place the assembly on clean shop towels to prevent debris from entering the injectors.

Step 4: Unbolt the Manifold

Remove the four (or sometimes five) bolts that hold the intake manifold to the cylinder head. On some D‑series applications, two lower bolts are accessed from underneath the car with a long extension. Use a 12‑mm socket for the manifold bolts and a 10‑mm socket for accessory brackets. As you remove each bolt, note its location — some are longer than others. Once all bolts are out, wiggle the manifold free. You may need to pry gently with a wide flat bar against the manifold mounting surface; be careful not to damage the head.

Step 5: Clean the Sealing Surface

With the old manifold removed, use a razor blade scraper to remove all traces of the old gasket and any carbon buildup. Wipe the surface with brake cleaner and shop towels until it is perfectly clean and dry. Inspect the head for cracks or warping — this is rare but should be checked before installing the new manifold.

Installing the Skunk2 Intake Manifold

This is where the upgrade comes to life. Follow the torque sequence and gasket instructions carefully to avoid vacuum leaks.

Step 1: Apply Gasket Maker

Skunk2 supplies a high‑quality composite gasket in the kit. For optimal sealing, we recommend applying a thin, even bead of high‑temperature gasket maker to the engine side of the gasket. Do not over‑apply — excess gasket material can squeeze into the intake ports and cause blockages. Place the gasket onto the head locating dowels (if present) or simply align it by hand.

Step 2: Position the Manifold

Lift the Skunk2 manifold into place. It is heavier than the factory unit due to thicker walls and larger plenum. Align all bolt holes and start each bolt by hand. Once all bolts are started, torque them in a star pattern to the manufacturer’s specification: typically 18–22 ft‑lbs for the main bolts and 10–12 ft‑lbs for the smaller accessory studs. Use a torque wrench — over‑torquing can warp the manifold.

Step 3: Check Clearance

The larger Skunk2 plenum may contact the A/C lines, hood liner, or throttle cable bracket. If interference occurs, you can gently bend hard lines out of the way (do not kink them) or slightly trim the throttle cable bracket. Some installers choose to remove the A/C altogether; that is a personal preference. Verify that the throttle body linkage operates freely before proceeding.

Step 4: Reinstall the Throttle Body

Use the original throttle body or upgrade to a larger unit (Skunk2 sells compatible throttle bodies). Install a new throttle body gasket and torque the bolts to about 10 ft‑lbs. Connect the TPS, IACV, and vacuum lines. Adjust the throttle cable so there is a small amount of slack (about 1/8 inch of play).

Reattaching the Fuel System and Sensors

Place the fuel rail and injectors back onto the Skunk2 manifold. The injector ports are the same as OEM, so they should snap in easily. Reconnect the fuel line and ensure the quick‑connect fitting clicks securely. Reinstall any remaining sensor connectors (engine coolant temperature sensor, knock sensor, oxygen sensor wires) that were unplugged. Refill the cooling system if you drained it, and reconnect the battery.

Initial Startup and Tuning

Turn the key to the “on” position without starting to prime the fuel pump. Check for fuel leaks around the rail and injector o‑rings. Start the engine and let it idle. It may hunt a bit as the ECU relearns due to the new manifold’s increased plenum volume. Inspect thoroughly for vacuum leaks — listen for hissing sounds and use a smoke machine or carburetor cleaner to spot leaks. If the idle stabilizes, take the car for a gentle test drive.

Tuning Considerations

While the Skunk2 manifold will run on a stock ECU with no immediate damage, the factory fuel and ignition maps are not optimized for the increased airflow. To fully realize the power gains (typically 8–12 hp at the wheels on a relatively stock D‑series), a proper tune is essential. Options include:

  • OBD1 ECU with a socketed chip (e.g., P28 or P06) burned with a custom tune
  • Standalone systems like HondaTech’s recommended Moates Ostrich or Hondata S300
  • Professional dyno tuning at a shop experienced with Honda engines

Budget an additional $200–$600 for tuning unless you have the tools and knowledge to do it yourself. Without a tune, you may experience a lean condition at wide‑open throttle, which can lead to detonation. Skunk2’s official site provides baseline maps for some setups, but dyno tuning remains the safest approach.

Cost Breakdown – Realistic Budget

Below is a detailed estimate including items you may need to purchase. Prices are approximate and can vary by region and retailer.

Item Estimated Cost
Skunk2 Intake Manifold Kit $300
Throttle Body Gasket $5
High‑Temp Gasket Maker $10
Coolant (if drained) $10–$15
Fuel Line Disconnect Tool $10
Tools (if none owned) $50–$100
Professional Dyno Tune $300–$600
Miscellaneous (shop towels, degreaser, brake cleaner) $20
Total (without tune) $350–$455
Total (with tuning) $700–$1,055

Consider that purchasing used aftermarket parts can cut costs, but always inspect used manifolds for cracks or stripped threads. For sourcing the manifold, reputable online stores like RockAuto or Summit Racing often carry Skunk2 products. You can also find discussions and installation tips on Honda‑dedicated forums such as Honda-Tech.

Common Installation Pitfalls and How to Avoid Them

  • Vacuum leaks: Even a small leak will cause rough idle and poor performance. Replace all rubber vacuum lines with silicone lines while you have access. Use a smoke test after installation.
  • Overtorqued bolts: The Skunk2 manifold uses aluminum flanges that can strip easily. Always use a torque wrench and follow the specs provided in the kit.
  • Inadequate clearance: The larger plenum may contact the alternator or power steering lines on some chassis models (such as the 92–95 Civic). Test fit before final torque and consider relocating brackets if necessary.
  • Forgetting to reinstall sensors: The IACV and MAP sensor are critical for idle and fuel management. Plug them back in before starting the engine.

Maintenance After Installation

Recheck all manifold bolts after 100 miles of driving as they may settle. Inspect the IACV and throttle body for carbon buildup every 30,000 miles. The larger plenum can collect oil mist from the PCV system; installing an oil catch can is a good preventative measure. Periodically examine the gasket surface for any signs of coolant or oil seepage.

Conclusion

Installing a Skunk2 intake manifold on your D‑series engine is a straightforward project that yields tangible performance benefits. The increased plenum volume and improved runner design allow the engine to breathe more efficiently, translating to stronger top‑end power and sharper throttle response. By following the steps in this guide, using the right tools, and investing in a proper tune, you will maximize the value of this upgrade. Take your time during the disassembly phase, label everything, and always prioritize cleanliness. With careful work, your D‑series will reward you with a more exciting driving experience for many miles to come.