Introduction

The Datsun 240Z is more than just a classic sports car; it is a piece of automotive history that continues to captivate driving enthusiasts. With its lightweight body, balanced chassis, and the legendary inline-six engine, the 240Z offers a pure driving experience that few modern cars can match. However, to truly unlock its potential, many owners turn to exhaust system upgrades. A well-designed exhaust not only liberates engine power but also transforms the car’s character. In this guide, we focus on installing a stainless steel Flowmaster exhaust system that can deliver a reliable 15 horsepower gain. Whether you are a seasoned mechanic or a weekend DIY enthusiast, this expanded walkthrough provides the insights needed for a successful upgrade.

Why Upgrade the Exhaust System on a Datsun 240Z

The factory exhaust system on the 240Z was designed for a different era—one where emissions and noise regulations were less stringent, but performance was not the primary focus. Decades later, the original steel pipes are often rusted, restrictive, and tuning inefficient. Upgrading to a modern system offers several quantifiable benefits:

  • Horsepower and Torque Gains: The stock exhaust has narrow piping and numerous bends that create backpressure. Replacing it with a larger-diameter, free-flowing stainless steel system reduces exhaust gas restriction, allowing the engine to breathe more freely. This translates into gains of 10–15 horsepower at the wheels, with a noticeable improvement in mid-range torque.
  • Improved Sound Quality: The characteristic straight-six engine note becomes deeper and more aggressive without being obtrusive. Flowmaster mufflers are known for their distinctive "chambered" sound—a mellow growl at cruising speeds that crackles under hard acceleration.
  • Fuel Efficiency: While not dramatic, a less restrictive exhaust can improve fuel economy by 3–5% under normal driving conditions, as the engine no longer has to work as hard to expel exhaust gases.
  • Weight Reduction: Factory exhaust systems on the 240Z consist of heavy steel and multiple mufflers. A modern stainless steel system shaves off 15–25 pounds, contributing to better acceleration and handling.
  • Durability and Longevity: Stainless steel resists rust and corrosion far better than the original mild steel, ensuring that the system lasts for decades rather than a few years.

Choosing the Right Exhaust System: Stainless Steel & Flowmaster

Stainless Steel vs. Mild Steel

When selecting an exhaust material, the choice often comes down to budget versus longevity. Mild steel is cheaper and easier to weld, but it rusts from the inside out due to moisture in the exhaust gases. Stainless steel, while more expensive, offers virtually indefinite life when properly maintained. For a car as cherished as the 240Z, stainless steel is the clear choice. Most aftermarket systems use 304 or 409 grade stainless; 304 has a brighter finish and better corrosion resistance, while 409 is more affordable but still far superior to mild steel.

Why Flowmaster?

Flowmaster has been a leader in performance exhaust technology for over four decades. Their chambered mufflers use engineered internal baffles to create a specific sound profile while providing optimal flow. For the 240Z, common choices include the Flowmaster 50 Series (moderate sound, good for daily driving) or the 40 Series (louder, more aggressive, ideal for track use). A complete stainless steel system from Flowmaster includes mandrel-bent tubing for smooth flow, polished tips, and all necessary hardware. Reputable sources like Flowmaster’s official website and Z-car specialists such as ZCar Depot offer system kits specifically designed for the 240Z.

Tools and Materials Needed

A proper installation requires preparation. Beyond the basic toolkit, you will need the following:

  • New stainless steel Flowmaster exhaust system (complete with muffler, pipes, clamps, gaskets, and hangers)
  • Socket set (metric sizes: 10mm, 12mm, 14mm, 17mm)
  • Combination wrenches (same sizes)
  • Breaker bar or impact wrench (for stubborn bolts)
  • Penetrating oil (e.g., WD-40 or PB Blaster)
  • Floor jack and two sturdy jack stands
  • Safety glasses and mechanic gloves
  • Angle grinder with cutting wheel (for removing old parts if needed)
  • Exhaust hanger removal tool (or a large screwdriver)
  • Gasket scraper and wire brush
  • Torque wrench (for precise tightening)
  • Rubber mallet (for alignments)

Step-by-Step Installation Guide

1. Vehicle Preparation and Safety

Begin by parking the 240Z on a level, solid surface. Let the engine cool completely if it has been running—exhaust parts can reach skin-burning temperatures. Disconnect the battery negative terminal to prevent accidental electrical shorts. Chock the rear wheels, then lift the rear of the car (using a jack at the differential or frame rails) and support it securely on jack stands. Never rely solely on the jack. For easier access, you may also place ramps under the front wheels, but ensure the rear is elevated.

2. Remove the Old Exhaust System

Start by spraying penetrating oil on all flange bolts, particularly the manifold-to-headpipe connection, the muffler flange bolts, and the hanger rubber grommets. Allow five minutes for the oil to work. Using a breaker bar or impact wrench, loosen and remove the nuts. On a 240Z, the stock system is attached with four bolts at the manifold, two flanged connections mid-system, and a series of rubber hangers. If bolts are seized and rounding, use a grinder to cut them off—but be careful not to damage the manifold studs. Once free, lower the old system from the car. It may come out in two or three sections. An assistant can help maneuver the heavy steel out from under the car.

3. Prepare the Manifold and New Components

With the old system removed, clean the exhaust manifold flange using a gasket scraper and wire brush. Remove any remnants of the old gasket. Inspect the manifold for cracks or warping—this is a common issue on early 240Z heads. If the manifold is cracked, now is the time to replace it with a header or a quality OEM piece. Apply a new exhaust gasket (usually included with the kit) to the manifold. Do not use grease or sealant on the gasket; it seals when the bolts are torqued.

4. Install the New Flowmaster System

Begin by loosely attaching the header pipe (downpipe) to the manifold using the supplied bolts and copper anti-seize compound (prevents future seizing). Leave the bolts finger-tight. Next, hang the first section of tubing leading to the muffler, using the new rubber hangers provided. Slide the muffler into position; it typically mounts in the original location behind the rear axle. Connect all sections using the band clamps or flange bolts. Ensure that pipes have at least 1 inch of clearance from the floor pan, brake lines, and fuel lines. Do not tighten anything fully until all pieces are loosely aligned.

5. Align and Tighten

Adjust the muffler tips so they are centered in the vehicle cutouts (if applicable). On a 240Z, the exhaust usually exits under the rear bumper on the driver side. Rotate each pipe section to avoid contact with the rear sway bar and the differential. Once satisfied, tighten all clamps and bolts to the manufacturer's specified torque. A good rule of thumb is 25–35 ft-lbs for flange bolts, and enough clamp torque to prevent leaks but not distort the pipes. Use a torque wrench for accuracy.

6. Check for Leaks and Final Inspection

Before lowering the car, start the engine (make sure the battery is reconnected). Listen for any hissing or ticking sounds at each joint. A small leak can be felt by holding your hand near the connection (be careful of hot surfaces). If you detect a leak, tighten that clamp or bolt slightly. Once satisfied, temporarily plug the exhaust tailpipe with a rag to create backpressure and listen for leaks. Then remove the rag. Rev the engine gently to 2000 RPM and confirm no drone or rattles. If everything is quiet, lower the car.

7. Post-Installation Drive and Break-In

Drive the car for 20 minutes to heat cycle the new system. Then park and re-tighten the clamps while the system is still warm (but not hot). This ensures metal-to-metal seal as everything expands. Re-check after 100 miles. Some settling is normal.

Performance Results and Dyno Verification

Many enthusiasts have verified the 15 horsepower claim on both stock and slightly modified L-series engines. A standard 240Z with a free-flowing exhaust, a K&N air filter, and a mild distributor tune can see wheel horsepower jump from 95 to 110. The gains are most pronounced between 3000 and 5000 RPM, where the engine delivers peak torque. On the dyno, the Flowmaster 40 Series muffler showed a maximum gain of 15.2 HP at 5200 RPM compared to the stock muffler (source: independent club tests). The sound also drops 2–3 decibels at idle but becomes more aggressive under throttle. For those seeking even more power, pairing the exhaust with a Z Therapy carburetor rebuild or a header can push total gains past 25 horsepower.

For further dyno data, check out ZCar.com forums where users have posted before/after sheets, or refer to Datsun Parts for verified test results.

Maintenance Tips for Your Stainless Steel Exhaust

  • Clean the Tips: Use a stainless steel polish and fine steel wool to maintain the shine. Avoid abrasive pads that can scratch.
  • Inspect Hangers: Rubber hangers can deteriorate from heat and oil. Replace them every 3–5 years to prevent sagging.
  • Watch for Rattles: Over time, pipes may shift and contact the chassis. Use spacer clamps or heat shields to silence any vibration.
  • Check Gaskets: The manifold-to-downpipe gasket is the most common failure point. If you hear a ticking at idle, replace it.

Conclusion

Upgrading your Datsun 240Z with a stainless steel Flowmaster exhaust system is one of the smartest performance modifications you can make. With a direct 15 horsepower gain, a richer sound, and added longevity, this weekend project yields daily driving enjoyment for years. The combination of improved flow, reduced weight, and proper tuning transforms the classic Z into a car that keeps pace with modern traffic while retaining its retro soul. Whether you choose the moderate 50 Series or the aggressive 40 Series, the result is a more responsive, more exciting 240Z. Gather your tools, order your Flowmaster kit from a trusted supplier, and give your Japanese legend the exhaust system it deserves.