Why Upgrade Your NA Miata Exhaust?

The Mazda MX-5 Miata (NA chassis, 1989–1997) earned its reputation as the world’s most popular two-seat roadster through lightweight construction, near-perfect 50:50 weight distribution, and a chassis that rewards driver input. The 1.6L and later 1.8L inline-four engines are willing but choked by the factory exhaust system—a convoluted cast-iron manifold, restrictive catalytic converter, and a muffler designed more for silence than flow. Swapping in a high-quality aftermarket exhaust addresses three areas: it reduces backpressure for modest horsepower gains, drops significant weight (the stock system is heavy), and most importantly, it transforms the acoustic experience. For many owners, the sound of a properly tuned exhaust is as integral to the Miata’s personality as the steering feel.

Choosing between MagnaFlow and Borla often comes down to budget, build quality, and tonal preference. Both brands have decades of experience and offer bolt-on kits for the NA Miata. However, installation costs, power gains, and long-term reliability differ enough to warrant a detailed comparison. Below we break down each system, discuss real-world dyno results, and provide honest guidance on what to expect when you open your wallet.

Understanding the NA Miata Exhaust Layout

Before comparing specific brands, it helps to know what a “cat-back” or “axle-back” system means for an NA. The stock exhaust consists of a four-into-one header (or a factory cast manifold), a downpipe, a front pipe with a catalytic converter, a resonator (on some years), and a muffler. Most aftermarket exhausts for the NA Miata are sold as cat-back systems—they replace everything from the catalytic converter back to the tailpipe. Many enthusiasts also replace the header and midpipe separately, but this article focuses on the cat-back portion since that is the most common entry-level upgrade and where MagnaFlow and Borla directly compete.

Both brands offer systems that feature mandrel-bent stainless steel tubing, which eliminates the crimping found in factory crush-bent pipes. That smooth inner surface reduces turbulence and improves exhaust velocity—one of the reasons even a cat-back swap can free up horsepower on these small-displacement engines.

MagnaFlow Exhaust Systems for the NA Miata

MagnaFlow has been manufacturing exhaust components since the mid-1990s and is known for its “straight-through” perforated-core muffler design. Unlike chambered mufflers that force gases to bounce through baffles, a straight-through design relies on acoustic absorption material (usually stainless steel wool) wrapped around a perforated tube. This architecture minimizes backpressure while still knocking down harsh frequencies.

MagnaFlow offers two primary options for the NA Miata: the 16228 (a universal-style cat-back) and the 15630 (a direct-fit system, though availability varies by year). Both use T-304 stainless steel and carry a limited lifetime warranty against corrosion and defects. The 15630 is designed to bolt up to the factory catalytic converter location, making installation straightforward for a home mechanic with basic tools.

Installation Costs: MagnaFlow

Professional installation for a MagnaFlow cat-back system typically ranges from $200 to $400 in labor, depending on your region and the shop’s hourly rate. Expect to pay more if the existing hardware is rusted—fasteners on 30-year-old Miatas often require torch work or cutting. Parts alone cost between $350 and $600 (retail), so the total installed price lands somewhere between $550 and $1,000. If you are handy with a jack and socket set, you can do the job in 1–2 hours in your driveway. MagnaFlow provides a template and instructions, but note that the hanger positioning on the universal kit may require minor tweaking with a rubber mallet or an extra exhaust hanger.

Performance Results: MagnaFlow

On a stock 1.8L NA Miata (1994–1997), dyno tests from enthusiast forums and shops like Flyin’ Miata show a peak gain of roughly 5–8 horsepower and 6–9 lb-ft of torque from a cat-back swap. Gains are concentrated in the mid-range (3,000–5,000 RPM) where the car is most often driven on the street. Throttle response sharpens noticeably—the engine feels less strained when pulling from 2,500 RPM. The sound is deep and aggressive without being obnoxious; MagnaFlow’s straight-through design produces a pronounced burble on overrun. Some owners note a slight drone at highway speeds (around 3,500–4,000 RPM), which can be mitigated with a resonated midpipe.

Sound Profile and Materials

MagnaFlow’s tone is often described as “muscular.” It emphasizes low-frequency bass, making the Miata sound like a larger-displacement engine. The 304 stainless steel construction resists rust and discoloration better than aluminized steel, but the outer shell can develop a golden heat tint near the muffler body after extended use. This is cosmetic only and does not affect performance.

Borla Exhaust Systems for the NA Miata

Borla Performance Industries has been in the aftermarket exhaust business since 1978, earning a reputation for durability and a distinctive “Borla sound” that avoids the raspy edge of some competitors. Borla’s patented “Aircraft-Quality T-304 Stainless Steel” and multi-core muffler design are hallmarks. For the NA Miata, Borla offers the 140019 (cat-back system for 1990–1997 models). It features a dual-exit outlet—two 3.5-inch polished tips that fill the factory bumper cutouts—and incorporates a large center resonator to control drone.

Borla’s muffler technology uses a combination of absorption and reflection chambers. Gases pass through a perforated core while sound waves are tuned by internal partitions. The result is a refined, slightly metallic tone that many describe as “European sports car” rather than “American V8.”

Installation Costs: Borla

Because the Borla 140019 is a direct-fit system, professional labor costs align closely with MagnaFlow—typically $250 to $450 for installation. The parts themselves are slightly more expensive, retailing between $450 and $700. Total installed cost often lands between $700 and $1,150. Borla gaskets and clamps are included, but you may need to reuse the factory hanger isolators if they are still pliable. DIY installation is rated as moderate difficulty; the main challenge is aligning the dual tips evenly in the bumper opening, which may require loosening the entire system and adjusting hanger positions.

Performance Results: Borla

Dyno results from Good-Win Racing and independent owners indicate Borla cat-back systems deliver 7–12 horsepower and 8–12 lb-ft of torque on a stock NA 1.8L. The torque curve is notably flatter than stock, with peak torque arriving slightly earlier—around 3,200 RPM versus the stock 4,000 RPM. This makes the car feel more responsive in everyday driving and helps maintain momentum in tight corners. Borla’s sound is smoother at idle and under light throttle, but it opens up with a clean, sporty note when you get on the gas. Minimal drone is reported because of the center resonator.

Build Quality and Warranty

Borla uses heavy-gauge T-304 stainless steel (typically 16-gauge) that feels substantial. The polished tips are mirror-finished and hold their shine longer than MagnaFlow’s brushed or satin finishes. Borla backs their systems with a limited lifetime warranty that covers defects in materials and workmanship but not rust-through if the car is driven in road-salt climates. Both brands offer similar corrosion resistance, but Borla’s thicker tubing adds a few pounds—approximately 18–20 lbs for the full system versus 14–16 lbs for MagnaFlow.

Head-to-Head Comparison: MagnaFlow vs. Borla

Choosing the right exhaust involves trade-offs. Below we highlight the key differences across four categories: cost, power, sound, and installation difficulty.

  • Installation Costs: MagnaFlow is generally cheaper to buy and install. Expect a total difference of roughly $150–$250 in favor of MagnaFlow. However, Borla’s near-perfect fitment can save time and frustration for the DIY crowd.
  • Power Gains: Borla consistently shows a 2–4 horsepower advantage over MagnaFlow on the same dyno. This is likely due to Borla’s lower restriction muffler design and slightly larger tube diameter (2.25″ vs. MagnaFlow’s 2.0″ on the NA). The torque curve is also broader with Borla.
  • Sound Quality: This is subjective. MagnaFlow is deeper and more aggressive—ideal if you want the car to sound “mean.” Borla is smoother and more refined, better suited for daily drivers who value comfort and minimal drone. If you plan to add a turbo or supercharger later, the Borla system’s smoother flow may handle forced induction better, though both brands work well with boost.
  • Weight: MagnaFlow saves about 6–8 lbs over Borla, primarily because of the thinner-wall tubing and smaller muffler case. Weight savings matter on a lightweight car like the Miata, but the difference is marginal in real-world driving.

Long-Term Reliability and Maintenance

Both systems are made from high-quality stainless steel, so corrosion is minimal. However, the packing material inside MagnaFlow’s straight-through muffler can eventually degrade (blow out) after 50,000–80,000 miles, causing the exhaust to become louder and raspier. Re-packing is not possible—you must replace the muffler section. Borla’s chambered design uses no packing material, so it never “blows out.” The tone stays consistent for the life of the vehicle. This is a significant advantage for owners who plan to keep their Miata for many years.

DIY vs. Professional Installation: What You Need to Know

Installing a cat-back exhaust on a 1990s Miata is one of the easiest aftermarket upgrades you can do. With the car on jack stands, you unbolt the old muffler assembly from the catalytic converter (two nuts and one stud), slide out the hangers, and reverse the procedure. Most systems weigh under 20 lbs and can be handled by one person. The only common hurdle is rusted bolts—soak them overnight in penetrating oil and use a breaker bar. If the stud breaks, you will need to drill and tap, which may push you toward a professional.

Professional installation is recommended if you lack a garage, tools, or mechanical confidence. Many shops will also inspect the rest of the exhaust system, recommend gasket replacements, and ensure proper alignment to prevent rattling against the chassis. Expect the labor charge to cover 1–1.5 hours of work. Alignment of the tailpipes is especially important for the Borla dual-exit system—if one tip sits higher than the other, it will look unfinished and may vibrate against the bumper.

Considerations Before You Buy

While the exhaust upgrade yields immediate satisfaction, you should also consider whether your emissions equipment is intact. In some regions, removing the catalytic converter or replacing it with a test pipe is illegal. Both MagnaFlow and Borla systems are designed to work with a stock catalytic converter. If you have already upgraded to a high-flow cat or a header, the gains from a cat-back will be additive. For example, pairing a MagnaFlow cat-back with a Racing Beat header has been shown to produce 14–18 whp on a properly tuned 1.8L.

Also, think about your driving use. If track days and autocross are your focus, the Borla’s broader torque curve helps you exit corners faster. If you primarily cruise on weekends and want the loudest, most aggressive sound for the dollar, MagnaFlow delivers more bang for the buck.

External Resources

For real-world owner reviews and dyno charts, visit these trusted communities and vendors:

  • MiataTurbo.net – Extensive build threads with dyno results for both brands.
  • Flyin’ Miata – Professional Miata tuner that sells and installs MagnaFlow and Borla systems.
  • Good-Win Racing – Independent dyno testing and exhaust comparison charts.

Final Thoughts

Upgrading the exhaust on your NA Miata is one of the best modifications you can make for the money—it improves power, reduces weight, and gives the car a personality it lacks from the factory. MagnaFlow offers a deeper, more aggressive tone at a lower price point, making it a solid choice for budget-conscious enthusiasts who want immediate character. Borla costs more but delivers slightly better power gains, a more refined soundtrack, and a muffler that will not degrade over time. Either choice is a significant step up from the stock system. The right decision depends on your priorities: if you want the best value and a raw sound, go MagnaFlow; if you want premium build quality and a sophisticated note that lasts forever, Borla is worth the premium.