Why the Flyin’ Miata Stage 2 Kit Is a Game-Changer for Your NB

The NB Miata (1999–2005) is already a beloved sports car, but its 1.8-liter engine leaves room for improvement from the factory. The Flyin’ Miata Stage 2 Performance Kit addresses the most restrictive points in the intake and exhaust systems, unlocking noticeable gains in horsepower and throttle response without requiring internal engine modifications. This kit is a logical next step for owners who have already sorted out suspension and tires and want more usable power for street driving or autocross.

Unlike a standalone ECU or forced induction setup, the Stage 2 kit is a bolt-on package that preserves daily-driver reliability. It includes a cold-air intake system, a ceramic-coated header, a high-flow mid-pipe, and a cat-back exhaust. Together, these components reduce backpressure, improve scavenging, and lower intake air temperatures. The result is a smoother powerband and a more engaging exhaust note.

This guide covers the full installation process in detail, from workspace preparation to final testing. Whether you’re a seasoned DIY mechanic or a Miata enthusiast tackling your first performance upgrade, you’ll find the steps, torque specs, and tips you need to get the job done right. For additional background on the kit’s design and dyno results, refer to Flyin’ Miata’s official product page and the Miata.net garage archives.

Tools, Parts, and Workspace Setup

Before you turn a wrench, gather everything you need. Running to the hardware store mid-installation is frustrating and can lead to mistakes. The Flyin’ Miata Stage 2 kit ships with all necessary gaskets, clamps, and hardware, but you’ll still need a solid set of hand tools and a safe workspace.

Required Tools

  • Metric socket set (8 mm to 19 mm) with extensions and a universal joint
  • Combination wrenches (10 mm, 12 mm, 14 mm, 17 mm, 19 mm)
  • Torque wrench capable of 20–80 ft-lb
  • Jack and two jack stands (4-ton capacity recommended)
  • Flat-blade and Phillips screwdrivers
  • Trim removal tool or plastic pry bar
  • Penetrating oil (e.g., PB Blaster or Kroil)
  • Oil catch pan (for coolant if you disconnect the header coolant line)
  • Safety glasses and mechanic’s gloves

Parts Included in the Kit

  • Cold-air intake with K&N-style filter and heat shield
  • Ceramic-coated 4-1 header with new gasket
  • High-flow catalytic converter mid-pipe
  • Cat-back exhaust system with muffler
  • All mounting hardware, clamps, and sensor extensions

Preparing the Vehicle

Park the car on a level surface and let the engine cool completely — the exhaust components reach operating temperatures above 600 degrees Fahrenheit. Disconnect the negative battery terminal using a 10 mm wrench. This prevents accidental grounding while you work near sensors and the starter. Raise the front of the car securely on jack stands placed under the front subframe jacking points. Never rely on the jack alone. For exhaust work, you may also want to raise the rear slightly to access the mid-pipe hangers.

Removing the Factory Intake and Exhaust

Removing the stock components is the most time-consuming part of the installation, especially if your Miata lives in a region where rust is common. Work methodically and use penetrating oil on any bolt that resists movement.

Stock Intake Removal

Start with the intake system since it’s the most accessible. Unclip the mass airflow (MAF) sensor connector and the intake air temperature (IAT) sensor. Loosen the hose clamps at the throttle body and the airbox lid using a flat-blade screwdriver or a 7 mm nut driver. Lift the airbox lid and filter assembly out of the car, then remove the lower airbox tray by pulling it upward off its rubber grommets. Finally, unbolt the resonance chamber mounted to the inner fender if your NB has one. Set the stock parts aside; you can sell them or keep them as spares.

Stock Exhaust Removal

The exhaust system is heavier and requires patience. Begin at the header: unbolt the factory heat shield using a 10 mm socket. Spray the four header-to-engine nuts with penetrating oil and wait five minutes. Use a 14 mm deep socket with a universal joint to reach the cylinder head nuts. Work from the center cylinder outward to avoid warping the flange. Once the nuts are off, lift the header off the studs and lower it out from underneath the car.

Next, remove the mid-pipe. Unbolt the two flanges at the catalytic converter and the two bolts at the muffler inlet. Support the mid-pipe with a jack stand or a second pair of hands, then slide it off the rubber hangers using a trim tool or a squirt of silicone lubricant. The muffler comes off last. Unbolt the muffler hangers at the rear and slide it out from under the bumper.

Pro tip: If any exhaust bolts snap during removal, use a left-hand drill bit and an extractor set. Replacing a stud on the NB Miata header is straightforward, but it adds time to the job.

Inspecting the Engine Bay

With the stock parts out, clean the engine bay. Wipe down the throttle body opening, check the condition of the coolant hoses near the header, and inspect the O2 sensor wiring for cracks. Now is the perfect time to replace the spark plugs and wires if they’re due; the intake removal provides excellent access to the coil packs and plug wells.

Installing the Flyin’ Miata Stage 2 Intake

The cold-air intake included in the kit routes the filter into the front bumper area, away from engine heat. This design improves volumetric efficiency compared to a hot-air intake mounted near the exhaust manifold.

Mounting the Heat Shield

Start by loosely installing the aluminum heat shield that comes with the kit. It bolts to existing holes in the inner fender and the radiator support. Use the provided M6 bolts and a 10 mm socket. Do not fully tighten yet — you may need to shift the shield slightly to align the intake tube.

Installing the Intake Tube and Filter

Slide the silicone coupler onto the throttle body inlet and tighten the clamp just enough to hold it in place. Connect the intake tube to the coupler and position the filter end inside the heat shield. Secure the filter to the tube using the supplied clamp. Once everything is aligned, tighten all coupler clamps to 5 ft-lb (check with your torque wrench on the low setting). Reconnect the MAF sensor and IAT sensor using the extension harness provided in the kit, which repositions the sensors to work with the new tube length.

Verify clearance: Turn the steering wheel lock-to-lock while the car is still on jack stands. Make sure the intake tube does not contact the inner tie rod or the sway bar at any point. If it does, loosen the couplers and rotate the tube slightly.

Final Intake Assembly

Bolt the air filter’s mounting bracket to the heat shield using the supplied M6 hardware. Double-check that the filter sits at least two inches off the ground; lower placement risks water ingestion during heavy rain. If you drive in wet conditions, consider installing the optional pre-filter sock (sold separately by Flyin’ Miata).

Installing the Flyin’ Miata Stage 2 Exhaust System

The exhaust installation requires working under the car, so confirm the jack stands are stable before you begin. The ceramic-coated header bolts directly to the cylinder head, and the mid-pipe and cat-back connect via slip-fit joints and heavy-duty clamps.

Header Installation

Apply a thin layer of anti-seize compound to the header studs. Install the new header gasket over the studs with the raised ring facing the head. Lift the ceramic header into position carefully; the coating is durable but can chip if struck against the subframe. Start all four nuts by hand to avoid cross-threading, then tighten them in a crisscross pattern using a 14 mm socket and torque wrench. The specified torque is 35 ft-lb for the header nuts. Reinstall the header heat shield if your kit includes one, or use the supplied heat wrap if you prefer.

Mid-Pipe and Cat-Back Installation

Slide the mid-pipe gasket onto the header outlet flange. Support the mid-pipe with a jack stand and bolt it to the header using the supplied hardware. Torque the flange nuts to 30 ft-lb. Next, apply exhaust sealant to the slip-joint between the mid-pipe and the cat-back, then slide them together. Secure the cat-back to the rubber hangers using the new isolation rings included in the kit. Tighten all band clamps to 35 ft-lb once the system is fully aligned.

O2 Sensor Reinstallation

The kit includes a bung extender for the downstream O2 sensor to maintain proper clearance from the transmission tunnel. Install the upstream O2 sensor into the header bung using a 7/8-inch O2 sensor socket. Torque to 30 ft-lb. Route the downstream sensor wire away from the exhaust and clip it to the existing harness using zip ties. Plug both sensors back into the chassis harness.

For more detailed torque specifications, consult the Mellens Miata factory service manual, which covers all fastener values for the NB chassis.

Reassembly, Leak Checks, and First Start

With all hardware installed, it’s time to reconnect components and verify the work.

Reconnecting the Battery and Checking for Leaks

Reconnect the negative battery terminal. Inspect every intake coupler, exhaust joint, and O2 sensor connection. A small exhaust leak at the header flange will cause a ticking sound and lean the air-fuel mixture, so be thorough. If you have a smoke machine, pressurize the intake system to detect vacuum leaks. Otherwise, spray a squirt of brake cleaner near the joints while the engine idles; a change in idle speed indicates a leak.

Starting the Engine

Start the engine and let it idle for two minutes. The exhaust will smoke briefly as the ceramic coating cures; this is normal. Listen for any rattles where the intake tube contacts the body or where the exhaust contacts the subframe. If you hear contact, loosen the affected clamps and reposition the pipe. Tighten again to the specified torque.

Torque Recheck

After the first heat cycle, the exhaust bolts can loosen as the gaskets compress. With the engine cool, recheck the header flange nuts (35 ft-lb), the mid-pipe flange (30 ft-lb), and the band clamps (35 ft-lb). This step prevents future leaks and ensures long-term reliability.

Road Testing and Performance Validation

Take the car on a test drive that includes city streets and highway cruising. Pay attention to the following:

  • Throttle response: The engine should feel sharper, especially between 3,000 and 5,500 RPM. If you notice flat spots, check for vacuum leaks at the intake couplers.
  • Exhaust tone: Expect a deeper, more aggressive note. Some droning between 2,500 and 3,000 RPM is normal for a cat-back system. If the drone is excessive, verify the muffler hangers are installed correctly and the exhaust is not contacting the differential.
  • Check engine light: If the CEL illuminates, scan for codes. Common codes after an intake/exhaust swap include P0171 (lean) or P0420 (catalyst inefficiency). A lean code usually means an intake leak; P0420 may require an O2 sensor defouler or ECU reflash.

Log your seat-of-the-pants impressions and compare them to the dyno charts available on the Flyin’ Miata website. The Stage 2 kit typically delivers a 10–15 horsepower gain at the wheels on a stock 1.8-liter NB, with corresponding torque improvements in the mid-range.

Maintenance Tips After the Upgrade

The Flyin’ Miata Stage 2 kit requires minimal additional maintenance, but a few habits will keep it performing well:

  • Inspect the air filter every 5,000 miles. Clean and re-oil it per the manufacturer’s instructions (typically every 30,000 miles).
  • Recheck exhaust gasket torque at the first oil change. Heat cycling can cause initial settling.
  • Keep the ceramic header coating clean. Avoid pressure washing directly at the coating; if it chips, touch up with high-temp header paint.
  • Monitor O2 sensor readings with a scan tool. A slow sensor response can indicate contamination from improper sealant use during installation.

For community advice and tuning tips, the Miata.net forum has an active NB Performance section with thousands of posts from owners running the Stage 2 kit.

Common Pitfalls and How to Avoid Them

Even experienced mechanics can encounter snags during an intake/exhaust swap. Here are the most frequent issues and their solutions:

Stuck Exhaust Nuts

The header-to-head nuts are exposed to heat and road salt. If they won’t budge after penetrating oil, apply localized heat with a propane torch. Do not use an impact gun until the bolt is free; the stud can snap inside the aluminum head, requiring a helicoil repair.

Intake Tube Rubbing

The cold-air intake tube passes close to the power steering lines on some NB models. If you hear a rubbing sound at full steering lock, wrap the tube with split-loom conduit or reposition the mounting bracket.

O2 Sensor Wire Length

Aftermarket headers often relocate the O2 bung. If the wire is taut, order a four-foot O2 sensor extension harness from a supplier like BMotorsports. Never splice O2 sensor wires with standard butt connectors; the voltage signal is sensitive enough that poor connections can cause false lean readings.

Conclusion

The Flyin’ Miata Stage 2 Performance Kit transforms the NB Miata from a fun, underpowered roadster into a genuinely quick car that rewards enthusiastic driving. The installation is well within the reach of a home mechanic with basic tools and a weekend to spare. By following the sequence outlined here — proper preparation, careful removal of stock parts, precise installation of the intake and exhaust, and thorough testing — you’ll end up with a reliable, powerful setup that makes every drive more exciting.

Take your time on the torque checks and leak tests, and don’t hesitate to reach out to the Miata community if you run into a stubborn bolt or a questionable sensor reading. The payoff is a car that sings from idle to redline, with the kind of immediate throttle response that reminds you why the Miata is still the most popular sports car ever built.