Installing Mishimoto BRZ headers is one of the most effective ways to unlock the FA20 engine’s hidden performance, sharpen throttle response, and give the Subaru boxer a throatier, more aggressive exhaust note. However, achieving those gains without headaches requires careful preparation, precise technique, and a few pro-level tricks. This guide walks you through every phase of the installation, from clearing the workspace to dialing in the ECU tune, so you get the most out of your investment.

Preparation and Safety

Rushing into a header swap often leads to stripped bolts, damaged gaskets, or leaks that sap power. A methodical approach saves time and money.

Tools and Supplies Checklist

Having the right tools on hand before you lift the car prevents frustrating trips to the hardware store mid-job. Beyond the basics, a few specialized items make the work smoother:

  • Socket set (3/8″ and 1/2″ drive) with metric sockets: 10mm, 12mm, 14mm, 17mm, and 19mm are the most common sizes.
  • Torque wrench capable of 20–80 lb-ft (1/2″ drive recommended for header bolts).
  • Ratchet and extension bars (6″ and 12″) plus a swivel adapter for tight angles.
  • Gasket scraper or razor blade to old gasket material.
  • Penetrating oil (like PB Blaster or Kroil) for stubborn bolts.
  • Anti-seize compound and high-temp thread locker (optional for specific fasteners).
  • Jack, jack stands (two pairs for safety), and wheel chocks.
  • Disposable gloves and shop rags.

Workspace and Vehicle Setup

Perform the installation on a level concrete floor. Raise the car high enough to work comfortably under the engine bay and underneath for exhaust connection. Use jack stands rated for the vehicle weight – never rely on the jack alone. Disconnect the negative battery terminal to prevent any accidental short circuits or electrical gremlins while working near the starter motor and sensors. Finally, let the engine cool completely if it has been run; hot exhaust components cause burns and expand, making bolt removal more difficult.

Removing the Factory Headers

Factory BRZ/FR-S/GT86 headers are restrictive and heavy. Removing them cleanly sets the stage for a trouble-free Mishimoto installation.

Accessing the Headers

Start by removing any components that block access to the header flanges and O2 sensors:

  • Intake manifold (or at least the intake tube and air box) – this gives better access to the driver-side rear bolts.
  • Heat shields – both on top of the headers and around the steering shaft.
  • Unbolt the front pipe or overpipe that connects to the header collector – often you need to loosen the muffler mounts to shift the exhaust back.
  • Carefully unclip the O2 sensor connectors (front and rear) to avoid breaking the tabs.

Dealing with Stubborn Bolts and Studs

Header bolts on older BRZs may be seized from heat cycles. Spray penetrating oil onto each nut and stud at least 15 minutes before wrenching. Use a six-point socket rather than 12-point to reduce rounding. If a bolt feels tight, apply steady pressure with a ratchet and extension – avoid impact guns that can snap studs. For the notoriously difficult lower passenger-side bolts, a swivel socket or flexible extension is nearly mandatory.

If a stud comes out with the nut, do not panic – this is common. Replace it with a new stud (Mishimoto includes new hardware, but you can also use OEM Subaru studs). Clean the threads in the cylinder head with a tap if needed.

Inspecting Gaskets and Flanges

Once the old headers are free, inspect the exhaust ports and the gasket surfaces. Factory gaskets are usually multi-layer steel and often reusable if not damaged, but Mishimoto recommends using new gaskets for a perfect seal. Also check the flanges on the old headers for warping – if they are uneven, the new header flanges will still seal fine on the engine side, but the collector gasket should be fresh.

Installing Mishimoto Headers

Mishimoto headers are designed with mandrel-bent tubing and smooth collectors for optimal flow. Proper alignment and torque are key to preventing exhaust leaks.

Surface Cleaning and Gasket Preparation

Use a gasket scraper and brake cleaner to remove all residue from the cylinder head mating surfaces. Even a small piece of old gasket causes a leak. Similarly, clean the collector flange where the header meets the front pipe. Apply a thin film of copper high-temp anti-seize on the header studs (not on the gasket itself) to ease future removal.

Alignment and Hand-Tightening Sequence

Fit the new header gaskets onto the studs (the OEM-style gaskets work well, or use the supplied units). Place the Mishimoto header over the studs, starting with the passenger side. Hand-thread all nuts a few turns before tightening any. Follow a cross pattern: tighten the center nuts first, then the outer ones, to draw the flange evenly. Once all nuts are snug by hand, switch to a torque wrench.

Torque Specs and Sequence

Mishimoto specifies 26 lb-ft (35 Nm) for the header-to-cylinder head nuts. Do not exceed this – overtightening can warp the flange or break studs. Re-torque after the first heat cycle (see post-install section). For the collector bolts (header to front pipe), use new gaskets and tighten to 30–35 lb-ft depending on the flange style. Use high-temp anti-seize on these bolts as well.

Reinstalling Components and O2 Sensors

Before fully tightening everything, check that the O2 sensor wiring is not pinched or touching the hot header tubes. Mishimoto headers include a bung for the wideband O2 sensor; use the factory sensor or a new one if needed. Apply anti-seize to the sensor threads (avoid getting any on the sensor tip) and tighten to 30 lb-ft. Reinstall any heat shields that fit (the Mishimoto unit may require trimming the OEM shield – if not using one, consider ceramic coating for heat management). Reattach the intake, battery, and any other removed parts.

Maximizing Performance Gains

Headers alone provide a significant bump in mid-range torque and top-end power, but pairing them with supporting modifications amplifies the results.

Pairing with a Full Exhaust System

A cat-back or axle-back exhaust with freer-flowing mufflers complements the header’s scavenging effect. For the best gains, replace the front pipe and overpipe as well – this reduces backpressure and reveals more horsepower. Be aware that uncorking the exhaust increases volume; consider a resonated front pipe or a quality cat-back to manage drone.

ECU Tuning – The Real Key

Without a tune, the factory ECU will adapt only partially to the increased flow, leaving gains on the table and potentially triggering a check engine light for the rear O2 sensor. A custom tune or a reputable off-the-shelf calibration (like those from Delicious Tuning or Ecutek) optimizes fuel and ignition timing for the new headers. Expect 15–20 whp on a dyno with a proper tune. Many BRZ owners also use an OpenFlash Tablet for self-tuning.

For DIY tuning, the FT86club.com tuning forum is an excellent resource for base maps and advice.

Ceramic Coating for Heat and Sound

Mishimoto headers come with a silver ceramic coating that helps reduce under-hood temperatures and retains exhaust gas velocity. After installation, the coating also gives a distinct metallic note to the exhaust sound. If you ordered an uncoated version, consider getting them jet-hot coated or wrapped with DEI exhaust wrap. Coating improves sound quality by reducing harshness and adds a slight performance benefit from lower intake temperatures.

Post-Installation Checks and Sound Optimization

The first start after installation is exciting, but a few verification steps ensure everything is sealed and the car runs properly.

Checking for Exhaust Leaks

With the engine cold, start it and let it idle. Feel around each connection (header flange, collector joint, O2 sensor bungs) for puffs of air. Listen for a ticking or hissing sound that speeds up with revs – that indicates a leak. For a thorough test, spray soapy water on the junctions; bubbles reveal leaks. Tighten the affected bolts slightly (with the engine off and cool) and recheck.

First Heat Cycle and Re-Torque

Drive the car gently for about 20–30 minutes to bring the headers up to normal operating temperature. Allow the engine to cool completely, then re-torque the header nuts to 26 lb-ft. The gaskets compress during the heat cycle, and this second pass locks the seal. Do not skip this step; it is the most common cause of post-install leaks.

Sound Characteristics and Adjustment

Mishimoto headers produce a deeper, more aggressive boxer rumble compared to stock. The sound level depends on the rest of the exhaust. If the volume is excessive, consider a resonated front pipe or a silencer in the axle-back. Some drivers also add a Helmholtz resonator to cancel drone at cruising RPM. Experiment with different combinations – the BRZ community has extensive discussions on sound setups; the Subaru BRZ Forum is a good place to browse.

Common Mistakes to Avoid

Even experienced mechanics can fall into these traps. Avoiding them saves time and money.

Over-Tightening Header Bolts

Using a breaker bar or impact wrench to tighten header nuts easily warps the flange or snaps the stud. Stick to 26 lb-ft with a torque wrench. If you break a stud, drilling it out in situ is a nightmare – the alternative is to remove the cylinder head, which is not a job you want on a weekend.

Neglecting the O2 Sensor Extension

Aftermarket headers often move the rear O2 sensor bung further downstream. The factory wiring may not reach. Use an O2 sensor extension harness (available from Mishimoto or generic vendors) to avoid cutting and splicing. Never force the wiring to stretch; it leads to sensor failure.

Ignoring Heat Management

Uncoated or unwrapped headers radiate enormous heat, which can boil the brake fluid, melt plastic wire looms, and increase intake air temperatures. If you did not get the ceramic-coated version, wrap the headers with DEI Titanium wrap (soak before wrapping for easier fit) and install heat shield tape on nearby components. Also consider a heat shield for the starter motor – prolonged heat exposure can shorten its life.

Long-Term Maintenance and Durability

Mishimoto headers are built from T304 stainless steel and designed to last the life of the car, but a few habits extend their lifespan.

  • Periodically inspect the collector bolts for looseness – they can back out from vibration.
  • Check the O2 sensor connection for corrosion, especially in snowy or salty regions.
  • If you track the car, re-torque the nuts after each race weekend. Heat cycles are extreme on track, and slight movement occurs.
  • Replace gaskets if you ever remove the headers again – cheap insurance against leaks.

For replacement parts or technical support, refer to the Mishimoto official website and their product documentation.

Conclusion

Installing Mishimoto BRZ headers is one of the most rewarding modifications for your Subaru/Toyota twin – it wakes up the engine’s character and delivers tangible performance. By following the preparation steps, using proper torque, pairing with a tune, and staying on top of post-install checks, you will enjoy a reliable, powerful, and great-sounding setup for years. Take your time, use the right tools, and do not hesitate to consult community forums for model-year specific tricks. The result is a car that drives like it should have from the factory.