Tools and Materials Needed

Before starting the installation, gather all required tools and the HKS Racing Exhaust system for your FD RX-7. Having everything ready ensures a smooth workflow and minimizes interruptions.

  • HKS Racing Exhaust system (specific to FD3S chassis)
  • Socket set (metric, 10mm, 12mm, 14mm, 17mm)
  • Combination wrench set (same sizes)
  • Torque wrench (ft‑lb range)
  • Jack and jack stands (minimum 2‑ton capacity)
  • Rubber mallet or dead blow hammer
  • Exhaust hanger removal tool (or long flathead screwdriver)
  • Penetrating oil (e.g., PB Blaster or WD‑40 Specialist)
  • Safety goggles and mechanic’s gloves
  • Anti‑seize compound (copper or nickel‑based)
  • Shop rags or paper towels

The HKS Racing Exhaust is a cat‑back system — confirm your kit includes the connecting pipe, muffler, gaskets, and all necessary hardware. Some kits also include new hanger rubbers or bolts; if not, reuse the factory ones in good condition.

Preparation and Safety

Workspace and Vehicle Setup

Park your FD RX‑7 on a level, solid floor. Engage the parking brake and place wheel chocks in front of and behind the front tires. Using a hydraulic jack, lift the rear of the car from the factory jacking point (or the diff housing) and place sturdy jack stands under the rear subframe or designated lift points. Never rely on the jack alone — always use jack stands.

Penetrating Oil Application

Exhaust bolts on a rotary engine endure extreme heat cycles and often rust. Spray penetrating oil on every nut and bolt you plan to remove — especially those connecting the exhaust to the catalytic converter and the hanger brackets. Allow the oil to soak for at least ten minutes while you prepare your tools. For stubborn fasteners, apply a second dose and wait another five minutes.

Safety Precautions

  • Wear safety goggles to protect your eyes from falling debris or oil.
  • Use mechanic’s gloves to avoid cuts from sharp exhaust edges.
  • Work in a well‑ventilated area — exhaust fumes and penetrating oil vapors can be hazardous.
  • Never work under a car supported only by a jack.

Removing the Stock Exhaust System

Start at the Rear: Muffler Section

Begin removal at the rear muffler. Locate the two rubber hangers supporting the muffler. Using an exhaust hanger removal tool or a long flathead screwdriver, pry the rubber mounts off the metal hanger pins. A small amount of soapy water can help slide them off if they are stuck. Once free, remove any bolts connecting the muffler to the mid‑pipe — typically two 12‑mm or 14‑mm bolts. Support the muffler as you remove the last bolt so it does not fall.

Mid‑Pipe and Flange Connections

Move forward to the flange where the exhaust connects to the catalytic converter. This joint usually uses two spring‑loaded bolts and a gasket. Use a socket and wrench to loosen the nuts — working back and forth to avoid binding. If the bolts spin with the nut, use a second wrench to hold the bolt head. Once loose, remove the nuts and set aside. You may need to tap the flange with a rubber mallet to break the seal if the gasket has bonded. Slide the mid‑pipe off the studs and lower it carefully.

Note: On some FD models, the catalytic converter is integrated into the downpipe. If you are only replacing the cat‑back section, you will not need to remove the downpipe or cat.

Removing Hanger Brackets

Along the length of the stock exhaust, you will find several hanger brackets attached to the underbody. Using the appropriate socket, unbolt each bracket. Keep the hardware organized — wrap bolts in a labeled bag or place them in a container. Once all hangers are free and all flange connections are undone, lower the complete stock exhaust system from the vehicle and set it aside. A helper can make this step easier, but it is manageable alone with careful handling.

Installing the HKS Racing Exhaust

Pre‑Install Check and Gasket Preparation

Unpack the HKS Racing Exhaust and verify all components are present. The system typically comprises a front pipe (or mid‑pipe) and a muffler section, plus gaskets and bolts. Inspect the flange surfaces on both the piping and the catalytic converter — they must be clean and free of old gasket material. Use a razor blade or wire brush to remove residue, and wipe with a rag. Apply a thin, even coat of anti‑seize compound to the threads of the new bolts to prevent seizing from heat.

Positioning the New Mid‑Pipe

Slide the front section of the HKS exhaust (the pipe that connects to the catalytic converter) into position under the car. Align the flange studs with the holes on the cat side. It can be helpful to tilt the pipe slightly as you maneuver it past the suspension components. Install the new gasket between the flanges, then hand‑tighten the nuts. Do not fully torque yet — you will adjust alignment later.

Attaching the Muffler Section

Reattach the rubber hangers to the metal pins on the muffler hanger brackets. The HKS system uses the factory mounting points, so no modification is needed. Slide the muffler onto the mid‑pipe connection — this joint typically uses a slip‑fit with a clamp or a flange with bolts. If it is a slip‑fit, clean the inside of the connector and apply a small amount of exhaust sealant (optional). Tighten the clamp or bolts lightly by hand.

Reinstalling Hanger Brackets

Bolt the included brackets (or reuse factory brackets) to the underbody. The HKS system may come with upgraded rubber hangers — if so, replace the old ones. Ensure each hanger is seated fully on the pin. The exhaust should hang freely without contacting the chassis or the driveshaft.

Final Alignment and Torquing

With all components loosely assembled, adjust the positioning of the exhaust. Push and pull the muffler and mid‑pipe so that there is equal clearance on both sides of the car. A common issue is the exhaust tip contacting the bumper cutout — shift the muffler slightly if needed. Once satisfied, torque all flange bolts and hanger bolts to the manufacturer’s specifications. For typical 10‑mm bolts, 30–35 ft‑lb is sufficient; for 12‑mm bolts, 40–50 ft‑lb. Do not overtighten — rotary engine exhausts expand significantly when hot.

Use a torque wrench for the cat flange bolts to avoid stripping the studs. After final torquing, double‑check that all clamps and nuts are secure.

Post‑Installation Checks

Leak Inspection

Start the engine and let it idle. Cover the tailpipe end with a rag for a few seconds to build back‑pressure, then listen for any hissing or puffing sounds along the exhaust joints. Alternatively, use a soap‑and‑water spray bottle on each flange — bubbles indicate a leak. If you detect a leak, tighten the affected bolts slightly (1/8 turn) and recheck. Avoid driving with an exhaust leak, as it can lead to incorrect air‑fuel ratios and possible engine damage.

Clearance Check

With the engine running, turn the steering wheel lock‑to‑lock and watch for any contact between the exhaust and the steering rack or driveshaft. Also check that the exhaust does not touch the differential housing or rear sway bar. If contact occurs, loosen the hanger bolts and reposition the exhaust, then retorque.

Sound and Vibration

Take a short test drive (1–2 miles) on smooth roads. Listen for rattles or drone at different RPM ranges. The HKS Racing Exhaust is designed to have a deep, refined tone, but if you hear metallic banging, re‑examine hanger placements. If drone is excessive at highway speeds, consider adding a resonated mid‑pipe or resonator — though this is rarely needed with the HKS system.

Benefits of the HKS Racing Exhaust

Upgrading to the HKS Racing Exhaust brings multiple performance and driving improvements to the FD RX‑7:

  • Improved exhaust flow — The mandrel‑bent tubing and straight‑through muffler design reduce back‑pressure, allowing the rotary engine to breathe more freely. This can unlock 5–15 horsepower at the wheels, especially when combined with an intake upgrade and ECU remap.
  • Weight reduction — HKS uses lightweight stainless steel (often T304) and a smaller muffler can than the stock system. Many owners report saving 10–15 pounds, which contributes to better handling and acceleration.
  • Enhanced sound — The HKS exhaust produces a distinctive rotary note — lower, more aggressive, yet without excessive drone. It is a favorite among enthusiasts for its balanced “deep bark” at high RPM.
  • Durable construction — T304 stainless steel resists corrosion and heat better than the factory mild steel. Full‑length welding and reinforced hanger mounts ensure long‑term reliability under track use.
  • Direct fitment — Designed specifically for the FD chassis (1989–1995 Mazda RX‑7), the HKS system uses factory mounting points and clears all suspension components. Installation is truly bolt‑on with no cutting or welding required.

Performance Tuning Considerations

To fully exploit the new exhaust’s potential, consider these complementary modifications:

  • ECU remapping — A less restrictive exhaust changes the engine’s volumetric efficiency. A stock ECU may run lean or rich at certain RPM ranges. A standalone ECU or a piggyback tuner (e.g., Power FC, Haltech, A’PEXi) allows you to adjust fuel and ignition maps for optimal performance.
  • Intake upgrade — Pairing the HKS exhaust with a high‑flow intake (e.g., HKS Super Mega Flow, AEM, or K&N) balances intake and exhaust flow. This combination can yield a 10–20 HP increase on ported engines.
  • Boost control — For FD models equipped with twin turbos, aftermarket downpipes and boost controllers (e.g., GReddy Profec, HKS EVC) further reduce back‑pressure and allow higher boost levels safely with proper intercooling.
  • Gaskets and hardware — Use new OEM or high‑temperature copper gaskets for all exhaust joints. Check torque specifications regularly, as heat cycles can loosen bolts.

Maintenance Tips for Longevity

Keeping your HKS exhaust in top condition requires minimal effort:

  • After washing the car, rinse the exhaust tips with water to remove road salt and brake dust, then dry them. Stainless steel can still develop surface rust if exposed to chlorides.
  • Every oil change, inspect the rubber hangers for cracking and the bolts for rust. Replace any worn hangers promptly to prevent the exhaust from sagging.
  • If you drive in harsh winter conditions, consider applying a high‑temperature clear coat (e.g., VHT) to the underside pipes to protect against salt spray.
  • Avoid using harsh chemical cleaners on the polished tip; a mild metal polish (like Mothers Mag & Aluminum) once a month will maintain its luster.

Conclusion

Installing the HKS Racing Exhaust on your FD RX‑7 is a rewarding modification that delivers measurable performance gains, weight savings, and an exhilarating soundtrack. The process is straightforward for anyone with basic mechanical skills and the right tools. By following the detailed steps above — from thorough preparation to post‑installation checks — you will ensure a leak‑free, aligned, and long‑lasting setup.

For further reading, visit the official HKS website for product specifications, or consult the RX‑7 Club forum for community tips and tuning advice. Performance shops such as Pettit Racing offer professional installation and custom mapping services specifically for FD RX‑7s.

When you fire up the engine after installation, you will immediately notice the difference — the iconic rotary sound, the improved throttle response, and the knowledge that your FD is breathing easier. Enjoy the drive.