Overview of Stillen Exhaust Systems for the Nissan 370Z

The Stillen exhaust system is one of the most popular aftermarket upgrades for the Nissan 370Z, offering a noticeable improvement in both sound and performance. Engineered specifically for the VQ37VHR engine, Stillen offers cat-back and axle-back configurations that feature mandrel-bent 2.5-inch or 3-inch stainless steel tubing, CNC-machined flanges, and high-flow resonators or mufflers. The design reduces backpressure while maintaining a deep, aggressive exhaust note without excessive drone on the highway. According to Stillen, pairing their exhaust with a compatible intake and tuning can yield gains of up to 15 horsepower at the wheels on a stock 370Z. This installation guide will walk you through the entire process, from gathering tools to performing a final test drive, so you can unlock that extra power and enjoy a more thrilling driving experience.

Tools and Materials Needed

Before you begin, ensure you have every item on the list below. Having the right tools on hand will prevent unnecessary interruptions and keep the job moving efficiently. Most of these tools are common in a home garage, but a few specialty items like a torque wrench and penetrating oil are essential for a safe, leak-free installation.

  • Stillen Exhaust System (cat-back or axle-back kit as purchased) – Includes all pipes, mufflers, clamps, gaskets, and hardware. Verify contents against the packing list before starting.
  • Socket set (metric, 10mm to 19mm) – For removing factory bolts and reinstalling new hardware.
  • Wrench set (combination wrenches, 10mm to 19mm) – Useful for tight spaces where sockets cannot reach.
  • Jack and jack stands (rated for 2 tons or more) – The 370Z sits low; lifting the rear end gives you the necessary clearance to work under the car safely.
  • Safety glasses – Protect your eyes from falling debris and penetrating oil spray.
  • Mechanic’s gloves – Prevent cuts from sharp edges and reduce mess from grease and oil.
  • Torque wrench (capable of 30-80 ft-lb) – Critical for tightening flange bolts and hangers to manufacturer specifications.
  • Penetrating oil (e.g., PB Blaster or WD-40 Specialist) – Loosens rusted bolts that are common on older exhaust systems.
  • Rubber mallet – Helps free stuck exhaust hangers without damaging the rubber isolators.
  • Flathead screwdriver or exhaust hanger removal tool – For prying off stubborn rubber isolators.
  • Rags and clean shop towels – For wiping down surfaces and checking for leaks after installation.

Take a moment to lay out all tools and parts. If you are working in a driveway, sweep the area to minimize the chance of losing small nuts or bolts.

Preparation Steps

Proper preparation ensures a safe, efficient installation. Follow each step carefully before you touch a single bolt.

  1. Park on a level, solid surface. Concrete is ideal; avoid gravel or uneven asphalt where jack stands may sink or tip.
  2. Engage the parking brake and chock the front wheels to prevent any rolling. The 370Z’s parking brake works on the rear wheels, so chocking the front provides extra security while the rear is lifted.
  3. Disconnect the negative battery terminal. Use a 10mm socket to loosen the clamp on the negative post. Tuck the cable away from the terminal. This step prevents any accidental short circuits if a wrench touches a live wire, and also resets the ECU, allowing it to adapt to the new exhaust’s airflow changes more quickly after reconnection.
  4. Allow the exhaust to cool completely. If you have just driven the car, wait at least one hour. Hot exhaust components can cause severe burns and make bolts expand, making removal harder.
  5. Raise the rear of the vehicle. Position the jack under the factory rear differential housing (the recommended lifting point for the 370Z). Lift until the rear tires are about six inches off the ground, then place jack stands under the designated lift points on the rear subframe. Never rely on the jack alone. Gently lower the car onto the stands and double-check that they are stable and level.

With the car safely secured, you can now move to the removal phase. Work slowly and methodically; if you encounter a stubborn bolt, don’t force it—apply more penetrating oil and wait a few minutes.

Removing the Stock Exhaust System

The factory exhaust on the 370Z is a single-piece cat-back system that hangs from four rubber isolators and bolts to the catalytic converters using two flanges. Removal is straightforward but requires patience with rusted hardware, especially if you live in a region that uses road salt.

  1. Locate and spray all exhaust bolts and nuts with penetrating oil. Pay special attention to the two flange bolts where the mid-pipe meets the catalytic converters (17mm or 18mm head), and the nuts on the exhaust hangers (10mm). Let the oil soak for at least five minutes.
  2. Remove the rear O2 sensor if your 370Z has one downstream of the catalytic converters. On later model years the sensor is mounted in the catalytic converter itself, so you may not need to touch it. However, if your exhaust setup requires removing the sensor, use an O2 sensor socket (22mm) and carefully unscrew it. Keep the sensor clean and set it aside.
  3. Unbolt the flanges at the catalytic converter. Using a socket and breaker bar (or ratchet), loosen the two nuts (or bolts) that hold the mid-pipe to the converter flanges. If they are extremely tight, apply additional penetrating oil and use a long-handled wrench for leverage. Once loose, remove them by hand and set them aside.
  4. Support the stock exhaust with a jack or a helper. The factory exhaust weighs approximately 25-30 pounds. Place a jack with a block of wood under the mid-pipe or have an assistant hold it. This prevents the weight from tearing the rubber hangers.
  5. Detach the exhaust hangers. There are four rubber isolators: two near the mid-pipe and two near the mufflers. Use a flathead screwdriver or a dedicated hanger removal tool to pry the metal rod out of the rubber isolator. Alternatively, apply a small amount of soapy water to the rubber to help the rod slide out. Work from front to back, supporting the exhaust as you go.
  6. Carefully lower the stock exhaust system. Once all hangers are free, slide the exhaust out from under the car. It may be necessary to rotate the pipes slightly to clear the rear axle or control arms. Take your time to avoid scratching the undercarriage or damaging the heat shields.
  7. Inspect the removed exhaust for any unusual wear. Look for rust holes, broken welds, or collapsed baffles that may have been restricting flow. This inspection can give you a clue about the condition of your drivetrain before you install the performance part.

Pro tip: If the flange bolts shear off (common on older cars), you may need to drill out the studs and replace them with new hardware. A set of stainless steel bolts and nuts from a hardware store can save future headaches. Stillen’s kit often includes new hardware, but keep the original bolts as backups.

Installing the Stillen Exhaust System

With the factory exhaust removed, take a moment to clean the flange surfaces on the catalytic converters using a wire brush. Any leftover gasket material or rust will prevent a proper seal and cause exhaust leaks. Now you are ready to install the Stillen system.

  1. Lay out the Stillen exhaust components. Most Stillen cat-back kits consist of a mid-pipe section Y-pipe (or two separate pipes) and a muffler section. Identify each part and loosely test-fit the connections before applying any gaskets or hardware.
  2. Apply the supplied gaskets to the catalytic converter flanges. Stillen typically provides metal-substrate gaskets that seal better than paper. Place them over the studs (or align them with bolt holes) on each catalytic converter. Do not use sealant here; the gasket alone is sufficient when properly torqued.
  3. Mount the mid-pipe section. Starting from the front, lift the mid-pipe into position and slide the flanges over the studs. Finger-tighten the nuts (usually 14mm or 17mm) before moving to the back. This allows for some adjustment as you align the entire system.
  4. Attach the rear muffler section. Connect the mid-pipe to the muffler section using the supplied band clamp or flanges. Again, hand-tighten only. The rubber hangers should be installed on the metal rods at this stage. Lubricate the rubber isolators with a small amount of dish soap and push them onto the hanger rods. Use a rubber mallet if needed to seat them fully.
  5. Check tip alignment and clearance. View the exhaust tips from behind the car. The tips should be centered in the bumper cutouts and sit at an even height. If they are crooked, loosen the mid-pipe flange and muffler clamps and adjust the position. A common cause of misalignment is twisting the mid-pipe when tightening. Have an assistant hold the tips in place while you tighten.
  6. Torque all bolts to specification. Use your torque wrench to tighten the catalytic converter flange nuts to 30-35 ft-lb (follow Stillen’s instructions if they differ). For band clamps, consult the supplied manual; typical values are 15-25 ft-lb. Avoid overtightening band clamps, as this can deform the pipe or strip the threads. Recheck hanger isolators to ensure they are fully seated.

Important: If your Stillen system came with a replacement Y-pipe, you may need to reuse the factory heat shields. Ensure the heat shields are reinstalled and not touching any part of the new exhaust, which could cause rattles or heat damage.

Final Inspection and Test Drive

Once the entire exhaust is bolted down and the tips are properly aligned, follow these steps to complete the installation.

  • Reconnect the negative battery terminal. Tighten the clamp securely. This resets the ECU, which will start the fuel trim learning process with the reduced backpressure.
  • Start the engine and let it idle. Listen for any immediate ticking sounds that indicate a leak at the flanges. If you hear a ticking that speeds up with RPM, shut off the engine and re-torque the flange nuts. A small puff of smoke or condensation near the joints is normal initially.
  • Check for exhaust leaks. While the engine is idling, use a rag or glove to block the tailpipe tips momentarily. This pressurizes the system and makes leaks more audible. Walk around the car and listen near each connection. If you hear a hiss, tighten the corresponding clamp or bolt. A helper can assist by revving the engine slightly.
  • Lower the car. Carefully raise the vehicle to remove the jack stands, then lower it back to the ground. Re-torque the wheel lug nuts to 80 ft-lb if you disturbed the wheelnuts during the process.
  • Take a short test drive. Drive for 10-15 minutes at varying speeds (city and highway) to let the exhaust settle and the ECU adapt. Pay attention to the following:
    • Sound quality: The Stillen exhaust should deepen at idle and become aggressive under throttle, but should not drone excessively at cruising speeds (around 2,000-3,000 rpm). If drone is bothersome, check that all hangers are properly installed and that the system is not touching the underbody.
    • Performance feel: The 370Z should feel more responsive, especially in the mid-range (3,500-6,000 rpm). The claimed 15-horsepower gain is typically realized with the intake and tune, but even a standalone cat-back will noticeably improve throttle response.
    • No rattles or vibrations: After driving, park again and inspect underneath for any signs of contact with the chassis, driveshaft, or suspension components. Adjust clearance if necessary.

Allow the exhaust to cool completely before performing a final torque check on all bolts after the first 100 miles. Heat cycles can cause nuts to loosen; a quick re-torque ensures long-term reliability.

Maintenance and Care Tips for Your Stillen Exhaust

Stainless steel exhausts are durable, but they still require some basic care to maintain their appearance and function for years.

  • Clean the tips regularly. Use a non-abrasive metal polish (e.g., Mother’s Mag & Aluminum Polish) to remove dirt and prevent pitting. Wipe down after every wash to keep the burnt-blue or polished finish looking fresh.
  • Inspect hangers and clamps every oil change. Over time, rubber isolators can crack and metal clamps can corrode. Replace any worn parts immediately to prevent the exhaust from sagging.
  • Watch for rust on flange bolts. Even with stainless hardware, exposure to road salt can cause galvanic corrosion. Apply a thin coat of anti-seize compound to bolts when reinstalling if you live in a snowy climate.

By following these simple steps, your Stillen exhaust will continue to deliver that deep VQ note and performance advantage for the lifespan of your 370Z.

Conclusion

Installing a Stillen exhaust system on your Nissan 370Z is a rewarding project that yields an immediate, satisfying improvement in sound and a measurable gain in horsepower. The task is well within the reach of an intermediate DIY mechanic, especially when equipped with the right tools and a clear step-by-step plan. By carefully removing the factory exhaust, properly aligning the Stillen components, and performing a thorough leak check, you’ll enjoy a professional-grade installation that enhances both the driving experience and the resale value of your car. For further reading, explore the official Stillen product page for warranty details and additional tuning options. You can also join dedicated 370Z owner forums such as The370Z.com for community tips and dyno results from other members who have performed the same upgrade.