Understanding Aftermarket Exhausts for the Rotary Engine

The Mazda RX-7 is a unique sports car that relies on the Wankel rotary engine, which operates on a completely different principle than conventional piston engines. Because rotaries have a high-revving nature and a distinct combustion cycle, the exhaust system plays an even more critical role in performance tuning. Aftermarket exhaust systems for the RX-7 are designed to reduce backpressure, improve scavenging, and unleash the engine's potential. Upgrading the exhaust can yield noticeable gains in horsepower and torque, often with minimal effort. But not all exhaust systems are created equal—choosing the right one requires understanding how the rotary engine breathes and what modifications best complement its characteristics.

Why the RX-7 Benefits from an Exhaust Upgrade

The stock exhaust system on the RX-7 is restrictive, featuring narrow piping, multiple catalytic converters, and mufflers that prioritize noise compliance over flow. For enthusiasts, this restriction robs the engine of top-end power and response. A high-performance cat-back system like the Borla unit replaces the section aft of the catalytic converter with larger-diameter, mandrel-bent tubing and high-flow mufflers. This frees up exhaust gas flow, allowing the rotary to spin more freely and reach higher RPMs with improved efficiency. The 13B and 20B rotary engines, particularly in turbocharged form, respond exceptionally well to reduced backpressure—contrary to some piston-engine myths, rotaries actually need free-flowing exhausts to avoid excessive heat buildup and to maintain proper scavenging at high RPM.

Cat‑Back vs. Axle‑Back vs. Turbo‑Back Systems

Before selecting an aftermarket exhaust, it’s important to understand the different types:

  • Axle‑Back: Replaces only the muffler section behind the rear axle. Minimal performance gain; mostly sound improvement.
  • Cat‑Back: Replaces everything from the catalytic converter back—including mid-pipe, resonator, and mufflers. Offers a good balance of power, sound, and ease of installation.
  • Turbo‑Back: Replaces the exhaust from the turbocharger outlet to the tailpipe, often including a downpipe and high-flow cat or test pipe. Largest gains but more expensive and may require tuning. The Borla Cat‑Back system we focus on here sits in the sweet spot for most RX-7 owners.

Borla Cat‑Back Exhaust System: Overview

Borla has been a trusted name in exhaust engineering for decades. Their cat‑back system for the Mazda RX‑7 (both FD3S and earlier models where applicable) is constructed from T‑304 stainless steel, mandrel‑bent tubing, and features the company’s patented multi‑core muffler technology. Every system comes with a million‑mile warranty, reflecting Borla’s confidence in its durability. The kit includes all necessary hardware and a detailed instruction sheet. Importantly, the Borla system is designed to bolt directly to the factory catalytic converter flanges, making installation straightforward even for a weekend mechanic.

Performance Gains: Up to 20 Horsepower

Borla advertises a gain of up to 20 horsepower at the wheels for naturally aspirated and mildly tuned turbo RX-7s. Independent dyno tests have confirmed these numbers—for example, on a 1993 FD3S with a stock turbo, the Borla cat‑back typically adds 15–18 wheel horsepower, with an extra 10–12 ft‑lbs of torque in the mid‑range. The power increase comes primarily from reduced backpressure; the OEM exhaust on the FD has a reputation for choking the motor above 6000 RPM. With Borla, the engine pulls hard all the way to redline. Even on older FB or FC models, the gains are significant enough to feel seat‑of‑pants.

Cost Savings: Up to $500 Less Than Competitors

High‑end Japanese exhaust brands like HKS, Apexi, and GReddy offer cat‑back systems for the RX‑7, but their prices often exceed $1,200–$1,500. Borla offers comparable—if not superior—T‑304 stainless construction, mandrel bends, and a similar power gain at a typical retail price of $700–$900. That’s a saving of $300–$500 or more, depending on the specific model and retailer. For budget‑conscious enthusiasts who still want quality, Borla represents exceptional value. Additionally, the lifetime warranty means you won’t pay for replacements due to corrosion or weld failure—a common issue with cheaper stainless systems that use 409-grade steel.

Installation Guide: Doing It Yourself

Installing a Borla cat‑back is a satisfying afternoon project that requires only basic hand tools. Follow these expanded steps for a leak‑free result:

  1. Preparation: Safely lift the rear of the car using jack stands on the frame rails. Apply penetrating oil to all exhaust hanger bolts and flange nuts a few hours ahead.
  2. Remove the Stock System: Unbolt the flange at the catalytic converter (two nuts, usually 14mm). Support the exhaust, then remove the rubber hangers from the mounting pegs with a pair of pliers or a hanger removal tool. Lower the factory exhaust carefully—it can be heavy and unwieldy.
  3. Test Fit the Borla Setup: Before final assembly, lay out all the Borla components—mid‑pipe, resonator section, muffler, clamps, and hangers. Make sure nothing is bent from shipping. Slide the hanger isolators onto the new pipe’s rods.
  4. Install the New System: Start at the catalytic converter end. Apply a thin bead of high‑temp exhaust sealant on the flange face (optional but recommended). Bolt the mid‑pipe to the cat, tightening to 30–35 ft‑lbs. Work rearward, connecting each section with the supplied band clamps. Do not tighten fully until everything is aligned.
  5. Adjustment: Once all sections are loosely assembled, check that the exhaust tips are centered in the bumper cutout and that there are no contact points with the underbody (especially around the rear differential and control arms). Then tighten all clamps to the specified torque (typically 40–50 ft‑lbs).
  6. Final Check: Start the engine and listen for leaks. A small puff of smoke at startup is normal from the sealant, but steady hissing means a loose clamp. Rev the engine and inspect the hangers for excessive movement. Take a short drive, then re-torque the clamps once the system has heat‑cycled.

Sound and Driveability

One of the most subjective aspects of an exhaust is the sound. The Borla cat‑back delivers a deep, aggressive note without being obtrusive at highway speeds. The patented multi‑core muffler cancels certain frequencies, reducing drone—a common complaint with straight‑through designs. Inside the cabin, you’ll hear a refined growl under acceleration, but conversation and radio volume remain comfortable. Outside, the exhaust announces your presence with authority, making the RX-7 sound like the sports car it is. On turbo models, the spool of the twin‑scroll turbo becomes more audible, adding to the driving experience.

Maintenance and Longevity

Borla uses #T‑304 aircraft‑grade stainless steel, which offers excellent resistance to rust and corrosion. In regions where roads are salted, the system will outlast most aftermarket competitors. However, it’s wise to periodically inspect the clamps and hangers for tightness; thermal expansion can cause them to loosen over time. The muffler packing material inside Borla’s stainless‑steel housing is rated for many thousands of miles, and because there are no fiberglass wraps to degrade, you won’t experience the “sound getting raspy” issue common with budget mufflers. Cleaning the tips with a stainless polish a few times a year will keep the system looking like new.

Comparison to Other Aftermarket Options

While Borla is an excellent choice, it’s worth understanding how it stacks up against other popular systems:

  • HKS Hi-Power: Known for its large, polished tip and deep tone. Similar performance but often $1,100+. HKS uses 409 stainless on some models—less corrosion resistant.
  • Apexi N1: Straight‑through design, loud and aggressive. Slightly lighter than Borla but can be droney. Requires more frequent tightening of slip‑joints.
  • Racing Beat: Another top contender, especially for NA rotaries. Racing Beat’s presilencer design is quieter but results in slightly less top‑end power. Price comparable to Borla but warranty is shorter.
  • MagnaFlow: Budget option, often around $500, but uses 409 stainless and can rust in salt‑belt states. Sound is more muted, and power gains are lower.

Performance Testing: Before and After

To verify the gains from a Borla cat‑back, we recommend a before‑and‑after dyno test. Many local tuning shops offer a three‑pull session for around $100. On a stock FD3S, you can expect baseline numbers around 220 whp (with manual transmission). After installing the Borla, a typical result is 235–240 whp—a gain of 15–20 horsepower. If you also upgrade the downpipe and intake, the exhaust will allow the engine to breathe even more freely, synergizing with those mods. Remember that dyno results vary with temperature, fuel, and engine condition, but the trend is consistently positive. For a seat‑of‑pants test, take your RX‑7 to an empty stretch of road in third gear at 2,500 RPM; hammer the throttle and note how quickly the tach climbs. After the swap, you’ll feel a sharper pull as the engine spins up.

Conclusion

Upgrading your Mazda RX‑7 with the Borla Cat‑Back Exhaust System is one of the smartest performance investments you can make. You gain up to 20 horsepower, save $400–$500 compared to other brands with similar power, and enjoy a deep, refined exhaust note that enhances the rotary experience. With a million‑mile warranty and simple bolt‑on installation, the Borla system offers unbeatable value for any RX‑7 enthusiast. Whether you drive an FB, FC, or FD, this exhaust will unlock the hidden potential of your rotary engine while keeping your wallet happy. For more information, check out Borla’s official product page, read real owner experiences on RX-7 Club forums, or find detailed dyno results at Rotary Engine Performance.