The Toyota GR86 continues to solidify its reputation as a driver’s car, blending a lightweight chassis with a naturally aspirated 2.4-liter flat-four engine. While the FA24 powerplant delivers a noticeable torque bump over its predecessor, the stock exhaust system remains one of the most restrictive components in the powertrain. A well-engineered aftermarket exhaust not only unlocks additional horsepower and torque but also refines the sound profile and reduces weight. In this detailed analysis, we examine dyno-verified results from two leading brands—GReddy and Armytrix—to show exactly how their exhaust systems increase performance on the GR86.

Understanding Exhaust Systems and Their Role in the Toyota GR86

The exhaust system’s primary job is to evacuate combustion gases from the engine as efficiently as possible. In the GR86, the stock system includes a cast-iron exhaust manifold, a mid-pipe with a catalytic converter, a resonator, and a muffler. Each component imposes trade-offs between noise suppression, emissions compliance, and flow restriction. The factory layout is designed to meet global sound regulations and durability standards, but it leaves significant headroom for aftermarket improvement.

Upgrading to a performance exhaust—whether a cat-back, axle-back, or full turbo-back (in turbocharged variants)—reduces backpressure and improves scavenging. Scavenging is the phenomenon where the pressure wave from one cylinder helps pull exhaust from the next cylinder. A less restrictive, properly tuned exhaust enhances this effect, allowing the engine to breathe more freely. The result is an increase in volumetric efficiency, which directly correlates to higher horsepower and torque output. For the GR86, even a cat-back exhaust can yield gains of 10–25 horsepower at the wheels when measured on a chassis dynamometer.

The Science Behind Dyno Testing

A dynamometer (dyno) measures an engine’s output by applying a load and recording power and torque curves. For chassis dynos like the Dynojet 224x or Mustang MD-500, the test is performed by strapping the vehicle down and running it through a simulated acceleration. The raw data must then be corrected for atmospheric conditions (temperature, barometric pressure, humidity) to produce standardized figures. The two most common correction standards are SAE J1349 and DIN 70020, with SAE often yielding slightly lower numbers than uncorrected results.

When evaluating an exhaust system, it is critical to run a baseline dyno pull with the stock exhaust, install the aftermarket part, and then repeat the test under identical conditions—same fuel, same ambient temperature, same gear, and same cooling procedure. Any deviation can skew the comparison. The results shown in this article were obtained from multiple independent tests on the same GR86 chassis, using a Dynojet 224x with SAE correction. The peak horsepower and torque are reported, but the shape of the curve is equally important. A system that broadens the powerband often delivers more usable performance than one that spikes at a narrow RPM range.

GReddy Exhaust Systems for the GR86

GReddy (Trust Co., Ltd.) has been a staple in Japanese performance parts since the 1980s. For the GR86, they offer multiple exhaust configurations, including the popular Supreme SP cat-back and the RS Racing cat-back. Both are constructed from T304 stainless steel, with mandrel-bent tubing and hand-welded tips. The Supreme SP features a straight-through muffler design and a polished finish, while the RS Racing uses a more aggressive canister shape and a burnt titanium tip option.

GReddy Dyno Test Results and Analysis

On a bone-stock 2022 Toyota GR86 with 93-octane fuel, the baseline dyno run recorded 200 horsepower and 175 lb-ft of torque at the wheels. After installing the GReddy Supreme SP cat-back exhaust system (part number 13601346), the vehicle was retested. The results showed a peak gain of 20 horsepower (now 220 hp) and an additional 15 lb-ft of torque. The power increase was distributed across the rev range, with notable improvements above 4,500 RPM where the stock exhaust becomes especially restrictive.

The torque curve also flattened in the mid-range, indicating better scavenging and reduced pumping losses. Importantly, the GReddy system did not require any ECU tuning to achieve these gains—it simply allowed the FA24 engine to operate more efficiently within the stock control parameters. The exhaust note deepened without becoming droning, a common complaint with less refined aftermarket systems. Weight savings amounted to approximately 12 pounds compared to the stock cat-back assembly.

Sound and Build Quality

GReddy’s craftsmanship is evident in the precise fitment and robust welds. The Supreme SP produces a sporty, refined tone under throttle and remains subdued during cruising. Drivers who want a louder, more aggressive sound may prefer the RS Racing variant, which features less internal packing and a larger tip diameter. Both options are heat-cycle resistant and include all necessary gaskets and hardware for a direct bolt-on installation.

Armytrix Exhaust Systems for the GR86

Armytrix specializes in high-end valved exhaust systems that allow the driver to control exhaust flow via a remote or smartphone app. Their T304 stainless steel cat-back for the GR86 (model AR-GR86-CB) includes dual electronically actuated valves, a straight-through muffler bypass, and a polished tip set. The valve opens or closes a secondary path, enabling a silent mode for daily driving and a fully open mode for maximum performance and sound.

Valvetronic Technology in Practice

The Armytrix valve system uses a vacuum-actuated or electronic actuator (depending on the kit) that responds to RPM, throttle position, or a manual remote. When closed, exhaust gases are routed through a traditional muffler section, keeping noise within legal limits. When open, the gases bypass the main muffler entirely, flowing through a straight pipe to the tips. This design gives the driver two distinct exhaust personalities without any mechanical swap.

Armytrix Dyno Test Results and Analysis

Baseline testing on the same GR86 produced identical stock figures: 200 hp and 175 lb-ft. After installing the Armytrix valved cat-back and testing in the open (valve open) configuration, peak horsepower rose to 225 hp—a 25-wheel-horsepower gain. Torque increased by 20 lb-ft to 195 lb-ft. The gain was slightly higher than the GReddy system, likely due to the fully open straight-through path offering the least restriction once the valves are open.

In the closed-valve mode, the Armytrix exhaust showed a gain of approximately 10 hp and 8 lb-ft over stock, reflecting the still-improved flow compared to the factory muffler. This flexibility is a major advantage for drivers who want performance on demand without compromising neighborly behavior. The dyno graph also revealed a broader torque plateau between 4,000 and 6,500 RPM, indicating strong scavenging characteristics. Weight reduction was about 10 pounds compared to the stock cat-back.

Sound and Build Quality

Armytrix systems are known for their exotic exhaust note—a deep, raspy tone that becomes howling at high RPM. The build quality is exceptional, featuring CNC-machined flanges, TIG welded joints, and a polished mirror finish. The valve mechanism is sealed against moisture and heat, and the control module is plug-and-play. Some users report minor drone at freeway speeds when the valve is closed, but this is largely dependent on vehicle load and gear selection.

Comparing GReddy vs Armytrix: Which Exhaust Is Right for You?

Both brands deliver substantial, dyno-verified gains on the GR86. The decision ultimately comes down to budget, sound preference, and feature set. Below is a head-to-head comparison of key attributes.

  • Peak Horsepower Gain: GReddy (+20 hp), Armytrix (+25 hp with valve open).
  • Torque Gain: GReddy (+15 lb-ft), Armytrix (+20 lb-ft with valve open).
  • Sound Control: GReddy offers no active valve; Armytrix includes remote-controlled valve.
  • Build Material: Both use T304 stainless steel; Armytrix valve housings are CNC aluminum.
  • Weight Savings: GReddy (-12 lbs), Armytrix (-10 lbs).
  • Price Range: GReddy typically $1,000–$1,300; Armytrix $1,800–$2,200 due to valve system.
  • Installation: Both are direct bolt-on; Armytrix requires connecting the valve control module to power.
  • Warranty: GReddy offers a limited lifetime warranty against defects; Armytrix offers 2-year warranty on electronics.

For enthusiasts who prioritize maximum power and the ability to quiet down the car at will, the Armytrix is an excellent investment. For those who want a proven, no-fuss upgrade with a classic sporty tone, the GReddy delivers excellent value.

Additional Performance Exhaust Brands for the GR86

While GReddy and Armytrix lead in dyno-verified testing, several other aftermarket exhausts deserve mention. HKS offers the Hi-Power and Legamax Premium lines, with gains around 15–18 hp. Borla provides an ATAK cat-back that produces a loud, aggressive sound with similar power gains. Injen has a cat-back system that emphasized torque curve enhancement. Each brand has its own tuning philosophy, and many independent dyno tests confirm gains in the 10–20 hp range for cat-back systems alone. Full header-back systems (such as those from JDM Exhaust) can push gains to 30+ hp, but they require a tune to address check engine lights caused by removed catalytic converters.

Installation Considerations and Tuning

Installing a cat-back exhaust on the GR86 is a straightforward bolt-on job for a competent DIYer or shop. Most systems come with new gaskets and hardware; the stock system can be removed in about 30 minutes using basic hand tools. Exhaust hangers made from rubber may require lubrication for removal. After installation, check for leaks at the flanges and ensure the tips do not contact the rear bumper or underbody heat shields.

For cat-back systems, no ECU reflash is required. The engine’s closed-loop fuel trims will adjust to the slight change in exhaust flow. However, if you pair the exhaust with a cold-air intake or a header, a custom tune from a reputable source like FT86 Speed Factory is highly recommended to maximize gains and avoid lean conditions. Tuning can unlock additional 10–15 hp on top of the exhaust gains alone. If you install a full header-back system that deletes the secondary catalytic converters, you will likely trigger a CEL for catalyst efficiency—a tune or defouler is necessary to keep the light off.

Frequently Asked Questions About GR86 Exhaust Upgrades

Will an aftermarket exhaust void my warranty?

In the United States, the Magnuson-Moss Warranty Act protects consumers from blanket warranty denials. A dealer must prove that the aftermarket part caused the specific failure to deny coverage. A cat-back exhaust alone is very unlikely to cause engine damage, so reasonable warranty claims on unrelated components should remain valid.

Do I need a tune after installing a cat-back exhaust?

No, a tune is not required for a cat-back system. The ECU can adapt fuel trims within a small window. However, a tune will optimize timing and fuel delivery to fully exploit the improved flow, especially if paired with other modifications.

What is the best exhaust for daily driving on the GR86?

For daily driving, a valved system like Armytrix offers the best of both worlds: quiet operation for commuting and open sound for weekend drives. Alternatively, the GReddy Supreme SP provides a moderate sound level that avoids drone while still sounding sporty under acceleration.

Conclusion

The Toyota GR86 responds exceptionally well to exhaust upgrades, and dyno testing proves that brands like GReddy and Armytrix deliver real, measurable horsepower and torque gains. GReddy offers high-quality, reliable gains with a classic sound, while Armytrix brings cutting-edge valvetronic technology that lets you tailor the exhaust note to your mood and environment. Both systems are bolt-on, require no tuning for a cat-back application, and transform the driving experience. Whether you prioritize maximum power or flexible sound control, investing in a dyno-verified exhaust is one of the most satisfying modifications for the GR86. Consult the manufacturers’ official sites and independent dyno charts to confirm the numbers for your specific vehicle configuration, and enjoy the new character your GR86 will gain.