Upgrading to a Stillen exhaust system is one of the most rewarding modifications you can make to your Infiniti G37. Not only does it unlock a deeper, more aggressive exhaust note, but it also frees up restriction in the factory exhaust, potentially adding a few horsepower and improving throttle response. This guide provides a thorough, step-by-step walkthrough of the installation process, covering everything from tool selection to final checks, so you can perform the job safely and confidently in your own garage.

Benefits of a Stillen Exhaust on the G37

Before diving into the installation, it's worth understanding what you’re gaining. Stillen, a well-respected name in Nissan/Infiniti performance, engineers its exhaust systems to be a true bolt-on upgrade. The typical Stillen cat-back system for the G37 features mandrel-bent 2.5-inch tubing, a Helmholtz resonator chamber for drone cancellation, and polished stainless-steel mufflers. Compared to the stock exhaust—which is heavy and restrictive with a muted tone—a Stillen system reduces weight, increases exhaust flow, and produces a refined yet sporty sound. Expect a noticeable improvement in mid-range torque and a more linear power delivery, especially when paired with a tune.

Required Tools and Materials

A successful installation begins with proper preparation. Gather the following items before you raise the car. Having everything on hand will prevent frustrating interruptions.

  • Stillen exhaust system – Verify you have all components: mid-pipe, mufflers, clamps, gaskets, and bolts. Lay everything out to inspect for shipping damage.
  • Socket wrench set – Metric sockets: 10mm, 12mm, 14mm, 17mm, and 19mm (depending on bolt heads). Long extensions and a swivel joint are helpful for tight spaces.
  • Jack and jack stands – A low-profile floor jack and two sturdy jack stands (3-ton capacity). Never rely on the jack alone.
  • Penetrating oil – PB Blaster or WD-40 Specialist. Exhaust bolts are often corroded from heat cycles.
  • Torque wrench – A ½-inch drive torque wrench capable of 25–80 ft-lb for precise tightening.
  • Safety goggles and gloves – Protect your eyes from rust and debris; mechanix-style gloves prevent cuts from sharp edges.
  • Rubber mallet or dead-blow hammer – Useful for gently persuading stubborn hangers.
  • Exhaust hanger removal tool (optional) – A specialized tool with hooks makes removing rubber hangers much easier.
  • Ramps (alternative to jack stands) – If you prefer, you can drive onto ramps, but ensure they are rated for your G37’s weight.

Pre-Installation Preparation

Proper preparation ensures a smooth job and reduces the chance of damage to your new exhaust or your vehicle.

1. Find a Safe, Level Workspace

Park your Infiniti G37 on a flat concrete or asphalt surface. Avoid gravel or uneven ground. Engage the parking brake firmly. Chock the front wheels if you’re raising the rear.

2. Raise and Securely Support the Rear

Using a floor jack, lift the rear of the car at the differential or rear subframe jacking point. Place jack stands under the designated lift points on the rear frame rails—never on the exhaust or suspension control arms. Lower the car gently onto the stands. Verify the car is stable before sliding underneath.

3. Apply Penetrating Oil

Spray penetrating oil onto every exhaust flange bolt, hanger bushing, and the rubber isolators. Allow it to soak for at least 10–15 minutes. For cars in the Rust Belt, a soak of 30 minutes or more is advisable. This step alone can save you from stripping bolts.

Removing the Factory Exhaust

The stock G37 exhaust is a one-piece cat-back system from the catalytic converters back to the mufflers, but it is joined by a mid-pipe to axle-back connection. Stillen systems typically replace everything from the catalytic converters rearward, though some variations are axle-back only—verify your kit.

Step 1: Disconnect the Mid-Pipe from the Catalytic Converters

Locate the two flanges where the exhaust connects to the catalytic converters. These are usually 14mm or 17mm bolts. Using your socket wrench with an extension, break them loose. If they are stubborn, use a breaker bar. Remove all bolts and set them aside—some may be reused if Stillen provides new hardware.

Step 2: Unbolt the Mid-Pipe/X-Pipe Connection

On the G37, there is a flange connecting the mid-pipe to the axle-back section (just forward of the rear axle). Remove these bolts as well.

Step 3: Remove the Stock Mufflers

The rear mufflers hang on three or four rubber isolators. Spray them again with penetrating oil. Use your hand or a hanger removal tool to pull the rubber hangers free from the metal tabs on the muffler. Some tabs are tight—wiggle and pull while supporting the muffler. It’s helpful to have a second person to guide the muffler down. Wrap the muffler in a rag to avoid scratching the bumper.

Step 4: Remove the Mid-Pipe

Slide the mid-pipe forward off the rubber hangers and out from under the car. You may need to lower it at an angle to clear the rear suspension brace. Be careful not to damage the oxygen sensor wires or the heat shields.

Pro tip: If the stock exhaust is rusted together, you can cut it with a reciprocating saw to make removal easier—but avoid cutting near fuel lines or brake lines.

Installing the Stillen Exhaust System

Now that the factory system is out, inspect the spare parts. Stillen typically includes new gaskets, bolts, and sometimes a new mid-pipe hanger. Lay the new exhaust out on the ground in order of installation: usually mid-pipe first, then muffler section, then tips.

Step 1: Test Fit the Components (Dry Fit)

Before applying any sealant or tightening bolts, loosely assemble the Stillen exhaust under the car. Hang the mid-pipe on the factory rubber hangers. Connect it to the muffler section loosely—just a few threads on the clamp bolts. This allows you to adjust positions for perfect tip alignment with the bumper cutouts. The G37 bumper openings are rectangular; the Stillen tips should be centered and not touching the bumper. Adjust by sliding the muffler hangers or repositioning the clamps.

Step 2: Install New Gaskets and Sealant

Use the provided gaskets (graphite or metal) at each flange. If there is no gasket for the slip-fit connections, apply a thin layer of high-temp exhaust sealant around the male end. This ensures a leak-free joint even under thermal expansion.

Step 3: Tighten All Connections

Starting from the front: tighten the flange bolts at the catalytic converters. Torque to 30–35 ft-lb (verify Stillen’s specs; never exceed). Then move to the mid-pipe to muffler connection. If using a band clamp, tighten gradually and alternately to compress the gasket evenly. Finally, tighten the hangers and ensure the muffler is not bouncing against the underbody. Recheck tip alignment before the final torque on all clamps.

Step 4: Attach Exhaust Tips

Stillen exhausts often come with separate polished tips that slide over the muffler pipes and are secured with set screws. Adjust them to the exact depth you prefer (flush or slightly protruding) and tighten the set screws. Do not overtighten or you may strip the threads.

Post-Installation Checks and Adjustments

After everything is bolted in, it’s time to verify the work is safe and sound.

1. Clearance Check

Crawl under the car (it should still be on jack stands) and inspect for any contact between the exhaust and the underbody, driveshaft, sway bar, or frame. A rattle here will be amplified when driving. Gently push the exhaust pipes away from any metal surfaces. If clearance is tight, you may need to loosen and reposition.

2. Torque All Fasteners to Spec

Using a torque wrench, go over every bolt and clamp. Typical values: flange bolts 30–35 ft-lb, exhaust manifold-to-cat bolts 25–30 ft-lb (if applicable), band clamps 40–50 ft-lb. Over-tightening can cause flange warping or strip threads. Under-tightening leads to leaks.

3. Check for Leaks

Start the engine and let it idle. With a gloved hand or a piece of tissue, feel around each joint for any air leaks. Alternatively, listen for hissing sounds. A small leak can cause a high-pitched whistle and affect emissions. Tighten any leaking connections. If a flange gasket is damaged, replace it.

4. Test Drive and Listen

Lower the car from the jack stands. Take a short test drive with the windows down. Listen for drone at highway speeds (Stillen’s Helmholtz chamber should minimize it) and any rattles over bumps. Note that the exhaust may smell a bit “hot” for the first few heat cycles—this is normal as oils burn off.

5. Re-Torque After Heat Cycles

After your first drive (approximately 50–100 miles), the gaskets will have compressed. With the exhaust cold, re-tighten all clamps and bolts. This step is often overlooked but critical to preventing leaks later on.

Common Installation Challenges and Troubleshooting

Even with careful preparation, you might encounter a few issues. Here’s how to handle them:

  • Rust-seized bolts: Use a propane torch to heat the bolt head (avoid flames near fuel lines). Let it cool and hit it with penetrating oil again. An impact wrench can also help.
  • Hanger removal is too difficult: Spray silicone lubricant on the rubber isolators, then use the hanger tool. A flathead screwdriver can pry them off, but be careful not to tear the rubber.
  • Exhaust tips are crooked: Loosen the muffler clamps and rotate the muffler canisters slightly. Adjust the hangers by bending the metal tabs (if they are adjustable) or shimming with washers.
  • Persistent drone: Stillen systems are known to be relatively drone-free, but if you experience resonance at certain RPMs, check that the Helmholtz chamber is not blocked or that the exhaust is not contacting the underbody.
  • Check engine light: Aftermarket exhausts rarely trigger a CEL because they retain the catalytic converters. If a light appears, check for leaks or an incorrectly routed O2 sensor. A mild tune can also disable downstream O2 monitors.

Performance Tuning After Exhaust Installation

Your Stillen exhaust is now installed, but to maximize the gains, consider complementary upgrades. An aftermarket intake (such as Stillen’s own dual intake system) reduces restriction on the intake side. A professional dyno tune or an off-the-shelf ECU flash (like from Ecutek or UpRev) will adjust air-fuel ratios and timing to take advantage of the improved flow. Many G37 owners report 10–15 horsepower gains from the exhaust alone, and another 10–15 from a tune. Furthermore, consider replacing the stock y-pipe with an HFC (high-flow catalytic converter) or test pipe for even more aggressive sound and flow, though this may affect emissions compliance.

Maintaining Your Stillen Exhaust

Stainless steel exhausts require little maintenance, but a few practices keep them looking pristine:

  • Clean the tips regularly with non-abrasive metal polish to prevent pitting from road salt.
  • Inspect hangers and clamps every oil change for signs of corrosion or loosening.
  • Avoid deep water crossings—waterlogged exhaust can crack warped flanges if hot.
  • If you live in a snowy region, consider applying a light anti-seize compound on the slip joints to prevent them from fusing over time.

Conclusion

Installing a Stillen exhaust on your Infiniti G37 is a project that rewards you with immediate auditory and performance satisfaction. By following this detailed guide—preparing your workspace, removing the factory system methodically, dry-fitting and adjusting the new components, and performing thorough post-installation checks—you can achieve a professional-level result in your own driveway. The aggressive growl at startup and the crisp note as you climb the RPMs will remind you every day that this was a worthwhile upgrade. For additional resources, refer to the Stillen official website for product specifics, and browse enthusiast forums like MyG37 for installation tips and owner experiences. If you encounter any stubborn technical issues, consult a professional technician—your car and your ears will thank you.