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RX-8 High-flow cat / midpipe

Your RX-8

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+5–10 whp (est.)
Medium$200–$6001–2 hrs
All RX-8 mods

Why do it

The factory catalytic converter is restrictive. A high-flow version frees up some power, especially when paired with a tune.

Heads up

Changing the catalytic converter can be illegal for street use where you live. We only link to parts that keep a catalytic converter. Check your state's emissions rules before buying.

Tools you'll need

Parts to buy

Always double-check fitment for your exact year, trim and transmission before buying. Prices change. ModBuddy doesn't earn money from these links.

Before you start

  • This replaces the catalytic converter pipe (midpipe). Only use a version that still has a catalytic converter for street driving.
  • The exhaust must be completely cold. Catalytic converters stay hot for a long time.
  • Soak every nut and the O2 sensor threads with penetrating oil, ideally the night before.

Steps

  1. Support the car

    • Raise the car and support it on jack stands. Leaving the floor jack lightly in place as a backup is a good idea.

  2. Remove the O2 sensor

    • Remove the two 10mm nuts holding the O2 sensor heat shield.
    • Unplug the grey sensor connector by pressing its tab.
    • With a 22mm wrench, loosen the sensor one turn, spray it again, snug it back, then remove it. Working it back and forth helps the oil in and protects the threads.

  3. Free the hanger and crossmembers

    • Spray silicone on the rubber hanger where the pipe's hook passes through, then work it off the hook.
    • Remove the eight bolts holding the two chassis crossmembers under the car and set the crossmembers aside.

  4. Unbolt the old pipe

    • Front flange: remove the three 14mm nuts. These locking nuts strip easily, so use plenty of oil and a socket plus a box-end wrench. A stud can snap. Most kits include new hardware for that reason.
    • Rear flange: back the nuts off the spring-loaded bolts and keep the springs.
    • Lower the old pipe out carefully. The catalyst inside is brittle, so don't drop it.

    Tip: Leave one front nut loosely threaded while you free the rear. It keeps the pipe from falling on you.

  5. Move the gaskets over

    • Keep the front gasket if it's undamaged, otherwise replace it.
    • Carefully tap the rear donut gasket off the old pipe with a flathead screwdriver and fit it to the new pipe.

  6. Install the new pipe

    • Bolt the front flange loosely first, then swing the pipe up into the rear flange and fit the spring-loaded bolts.
    • Tighten the front flange evenly (CorkSport specifies 16–18 ft-lb for their pipe's hardware). Tighten the rear bolts until there's about 1mm between the spring coils.

  7. Reinstall the sensor and crossmembers

    • Put anti-seize on the O2 sensor threads, reinstall it and reconnect the plug without twisting the wire.
    • Reinstall the crossmembers (CorkSport lists 22–28 ft-lb for those bolts) and the rubber hanger.

  8. Test for leaks

    • Lower the car, start it and listen for ticking or puffing at the joints.
    • If you hear a leak at the rear flange, check that both spring bolts are compressed evenly.

How to know it worked

Safety first

  • Park on flat, solid ground, set the parking brake and chock the wheels.
  • Use jack stands rated for your car. Never get under a car held up only by a jack.
  • Let the engine and exhaust cool completely before touching them.
  • Disconnect the negative battery terminal before unplugging sensors or electrical parts.
  • Wear safety glasses, and gloves around sharp heat shields and hot fluids.
  • Tighten bolts to the torque spec in your factory service manual.
  • If a step doesn't match your car or you're unsure, stop and ask a shop.

These are overview steps written to help you plan the job. Always follow the instructions that come with your part and the procedures and torque specs in your factory service manual. Horsepower is an estimate; results vary.