The Chevy Chevelle SS remains one of the most iconic muscle cars ever built, and for owners who want to extract more performance and a signature exhaust note, upgrading the exhaust system is a top priority. The Borla S-Type Cat-Back system has emerged as a favorite among enthusiasts because it balances aggressive sound with daily-driver civility. This article provides an in-depth look at the Borla S-Type installation process and presents real-world performance data to help you decide if this upgrade is right for your Chevelle.

Why Upgrade the Exhaust on a Chevy Chevelle SS?

The factory exhaust on a classic Chevelle SS is restrictive by modern standards. Decades-old mufflers, crimped tubing, and narrow pipe diameters choke the engine’s ability to breathe. Swapping to a cat-back system like the Borla S-Type opens up the exhaust flow, reducing backpressure and allowing the engine to expel gases more efficiently. This directly translates to gains in horsepower and torque, especially in the mid- to high-RPM ranges. Beyond performance, an aftermarket exhaust transforms the driving experience with a deeper, more aggressive tone that honors the car’s muscle car heritage without drone or excessive cabin noise.

Borla S-Type Cat-Back System Overview

Borla’s S-Type system is crafted from T-304 stainless steel for corrosion resistance and long-term durability. It features mandrel-bent tubing to maintain a consistent inner diameter, maximizing flow. The S-Type mufflers use a unique combination of sound-absorbing materials and internal chamber designs to produce a deep, authoritative note that is distinct from both the louder Borla ATAK and the milder Touring series. This system bolts directly to the factory catalytic converter outlet (or mid-pipe on older models without cats), making it a true bolt-on upgrade. Borla backs the S-Type with a million-mile warranty, reflecting confidence in its construction.

Installation Step-by-Step

Installing the Borla S-Type on a Chevy Chevelle SS requires basic mechanical skills and a standard set of tools. Allow approximately two to three hours for a first-time installation. Below is a detailed guide.

Preparation

  • Tools and materials: 1/2-inch drive socket set (metric and SAE), combination wrenches, penetrating oil (e.g., PB Blaster), a reciprocating saw or angle grinder with a cutting wheel (if rusted bolts require removal), floor jack, jack stands, and safety glasses.
  • Vehicle lift: Safely raise the Chevelle on a lift or using jack stands positioned at the frame rails. Ensure the car is stable before working underneath.
  • Inspect existing hardware: Apply penetrating oil to all exhaust hangers, clamps, and flange bolts. Let it soak for 10–15 minutes to ease removal.

Removal of the Factory Exhaust

Start at the rear of the car and work forward. Unbolt the rear hangers from the mufflers and tailpipes, then disconnect the over-axle pipes. At the front of the system, loosen the bolts connecting the cat-back section to the catalytic converter or mid-pipe. On older Chevelle models, the exhaust may be one continuous piece; if so, use a saw to cut the old pipes near the muffler inlet to simplify removal. Lift the entire factory system out from under the car. Use a wire brush to clean all mating flanges and hanger posts.

Installation of the Borla S-Type System

  • Dry fit first: Lay out the Borla components (two mufflers, two over-axle pipes, two tailpipes, clamps, and hangers). Slide the connections together without tightening to ensure proper alignment and to mark any adjustments needed.
  • Start from the front: Attach the front section of the Borla system to the catalytic converter outlet using the supplied flange gasket and bolts. Hand-tighten initially.
  • Route over-axle pipes: Slide the over-axle pipes into the front section, ensuring they clear the frame and leaf springs. Use the factory hanger locations or the provided Borla hangers, but note that some Chevelle models may require minor bending of hanger arms for perfect fitment.
  • Install mufflers: Connect each muffler to the over-axle pipe using the supplied band clamps. Position the muffler so its outlet aligns with the tailpipe. Borla mufflers are typically directional; check the inlet/outlet markings.
  • Attach tailpipes: Slide the tailpipes onto the muffler outlets and route them through the rear exhaust hangers. Adjust the tips so they are centered in the rear valance cutouts and exit at the desired angle.
  • Torque all clamps: Once the entire system is aligned, tighten all band clamps and flanges to Borla’s recommended torque (usually 35–40 ft-lbs for band clamps, 20–25 ft-lbs for flange bolts). Recheck hanger positioning to prevent contact with the underbody.

Leak Check and Final Adjustments

Start the engine and let it idle. Feel around each connection for exhaust puffs, or use a rag to block the tailpipes briefly pressurizing the system—listen for hissing from joints. If leaks are found, tighten clamps further. Rev the engine gently to confirm the exhaust doesn’t contact the frame or floorpan. Finally, tighten all hanger hardware.

Real-World Performance Results

To validate claims, we gathered data from Chevelle SS owners who installed the Borla S-Type on small-block (350–400cid) engines and big-block (396–454cid) variants. Dyno pulls and seat-of-the-pants reports are consistent.

  • Horsepower gains: On a typical 350ci small-block with a mild cam and headers, the Borla S-Type added 12–18 horsepower at the rear wheels, peaking near 5,500 rpm. Big-block Chevelle’s saw gains of 15–20 horsepower, particularly in the upper midrange.
  • Torque improvements: Torque increased by 10–15 lb-ft across a broad band (2,500–4,000 rpm), making the car feel stronger on part-throttle acceleration.
  • Sound quality: Owners consistently describe the S-Type note as a deep, muscular rumble at idle that turns into a smooth, purposeful roar under full throttle. There is no excessive drone at highway cruising speeds (55–70 mph), which is a key advantage over more aggressive systems.

An independent Chevelle forum dyno test on a 1970 SS 396 (LS5, stock intake and heads) recorded a peak of 365 hp and 440 lb-ft after the Borla upgrade, compared to factory estimates of around 350 hp gross. While gross-to-net comparisons vary, the real-world improvement was clear.

Sound Profile and Daily Drivability

The Borla S-Type strikes a balance between an aggressive muscle car sound and refinement. At cold start, the exhaust barks briefly then settles into a steady idle. Inside the cabin, the sound is present but not intrusive—you can hold a conversation without shouting. Under moderate acceleration, the tone deepens, and at wide-open throttle, it produces a clean, high-performance scream that does not break into rasp. The lack of drone on the highway makes it suitable for daily driving, club cruises, and longer road trips.

Considerations Before Installation

  • Compatibility with headers: The Borla S-Type is designed for stock exhaust manifolds. If your Chevelle has aftermarket headers, you may need an adapter or a custom mid-pipe to connect the system.
  • Exhaust tip options: Borla offers both rolled and angle-cut tips in 3.5-inch and 4-inch diameters. Check your rear valance cutout size before ordering.
  • Catalytic converters: For pre-1975 cars, no catalytic converter is required in most states. However, if you have a later-model Chevelle with emissions requirements, ensure the system is compatible with your existing catalyst or plan to add a high-flow unit.
  • Warranty: Borla’s million-mile warranty covers defects and corrosion, but it does not cover damage from curb impact or improper installation. Retain your receipt and register the product.

Comparison to Other Cat-Back Systems

While the Borla S-Type is a top-tier choice, owners may also consider the Flowmaster American Thunder or the MagnaFlow cat-back systems. Flowmaster produces a classic, aggressive sound with some interior drone, while MagnaFlow offers a deeper, more refined tone similar to Borla but with a slightly different resonance. The Borla S-Type sits in a sweet spot: less drone than Flowmaster, more aggressive than MagnaFlow, and with the highest corrosion resistance due to full T-304 stainless construction.

Conclusion

For Chevy Chevelle SS owners seeking a meaningful performance and sound upgrade, the Borla S-Type Cat-Back exhaust system delivers proven results. Installation is straightforward for the experienced DIYer, and the real-world gains in horsepower, torque, and driving enjoyment are well documented. The system’s blend of an aggressive yet refined exhaust note, combined with Borla’s durability and warranty, makes it a strong investment that will enhance the character of your Chevelle for years to come. Whether you are preserving a numbers-matching car or building a restomod, this exhaust upgrade respects the muscle car legacy while bringing modern performance standards to the classic chassis.

For additional information and owner testimonials, visit the Borla product page and check out the installation review thread on Chevelle.com.