Introduction: Why Aftermarket Headers and What to Expect

Upgrading your vehicle’s exhaust system with aftermarket headers is one of the most effective ways to unlock horsepower, improve throttle response, and sharpen the engine’s sound. By replacing the restrictive factory exhaust manifolds with free-flowing headers, you allow spent gases to exit the combustion chambers more efficiently. This reduces backpressure, lowers cylinder temperatures, and can yield gains of 10–20 horsepower or more when paired with a proper exhaust system. Two of the most respected names in the header market are Flow Master and Hedman. Both manufacturers offer products that cater to different budgets and performance goals, but their installation procedures share many common principles.

This expanded guide will walk you through every stage of a successful header installation, from tool selection and safety preparation to post-installation checks and long-term maintenance. Whether you are installing a set of Flow Master’s stainless steel long tubes or Hedman’s budget-friendly ceramic-coated shorties, these tips and tricks will help you avoid common pitfalls and achieve a leak-free, reliable setup. Let’s get started.

Tools and Safety Preparation

Having the right tools on hand before you begin will save hours of frustration. Header installation often requires reaching awkward angles and dealing with rusted fasteners. Below is a comprehensive list of what you’ll need, along with reasons why each item matters.

  • Socket set (3/8″ and 1/2″ drive, metric and SAE) – Most header bolts are 5/16″ or 8 mm. A deep socket may be needed for long studs.
  • Combination wrench set – For final tightening in tight spaces. Flex-head gear wrenches are a lifesaver.
  • Torque wrench (½″ drive, 10–100 ft-lb range) – Over-tightening can warp flanges; under-tightening causes leaks. Accurate torque is essential.
  • Gasket scraper – A sharp, sturdy scraper removes old gasket material without gouging the cylinder head surface.
  • Wire brush or drill with wire wheel – Clean bolt holes and studs before installing new headers.
  • Jack and jack stands (or vehicle lift) – Most header installations require working under the vehicle. Never rely on a jack alone.
  • Penetrating oil (e.g., WD-40 or PB Blaster) – Spray exhaust manifold bolts the night before to ease removal.
  • Safety glasses and gloves – Rust, debris, and hot surfaces demand eye and hand protection.
  • Shop rags and a drop cloth – Keep your work area clean and catch any spilled coolant or oil.
  • Anti-seize compound – Apply to header bolts and studs to prevent corrosion and make future removal easier.
  • New header gaskets and bolts (if not supplied) – Many header kits come with gaskets and hardware, but aftermarket high-quality gaskets (e.g., Remflex or Percy’s) can improve sealing.

Before you touch a single bolt, park the vehicle on a level surface, disconnect the negative battery terminal, and allow the engine to cool completely. Hot exhaust components can cause severe burns. If your vehicle has an aftermarket alarm or radio memory, note that the battery may lose settings – a memory saver can help.

Pre-Installation: Removing the Old Manifolds

Removing stock exhaust manifolds is often the most time-consuming part of the job. Rusted bolts break, access is limited, and you may need to remove other components to reach the manifolds.

Step 1: Clear the Work Area

Remove any components that obstruct access to the exhaust manifolds. This commonly includes:

  • Upper and lower air intake tubes
  • Throttle body (if necessary – you may only need to unbolt the intake tube)
  • Spark plugs (on some engines, especially with long-tube headers)
  • Alternator bracket or power steering pump (on tight engine bays)
  • EGR valve and associated tubing

Take photos before disconnecting anything so you know how to reassemble. Label connectors with tape or zip ties.

Step 2: Soak and Remove Bolts

Spray the exhaust manifold bolts with penetrating oil. Wait 15 minutes. Start with the outermost bolts and work inward. Use a six-point socket rather than a twelve-point to avoid rounding. If a bolt feels stubborn, tighten it slightly first to break the rust bond, then loosen. For bolts that still refuse to move, apply heat with a propane torch (be mindful of fuel lines, wiring, and plastic). When a bolt snaps, you’ll need to extract it with a bolt extractor set – this is a common reason header installations take two days instead of one.

Step 3: Clean Mating Surfaces

Once the old manifolds are free, use a gasket scraper and wire brush to remove all old gasket material, carbon deposits, and rust from the cylinder head exhaust ports. The surface must be flat and clean – any debris will cause a leak. Wipe the area with brake cleaner and a lint-free rag. Inspect the head for cracks or warpage (rare but possible).

Step 4: Test Fit the New Headers

Dry-fit each header without gaskets to check clearance. Rotate the engine by hand (using a socket on the crankshaft bolt) to ensure the header tubes do not hit the frame, steering shaft, clutch linkage, or spark plugs. This is critical for long-tube headers. If you see interference, note where material may need to be dented or clearanced – sometimes you can dimple the tube slightly with a hammer and a block of wood (for mild steel headers only). For stainless steel headers, consider using a set of aftermarket spark plug wire separators or angled plug adapters to improve clearance.

Installing Flow Master Headers

Flow Master headers are built in the USA and are known for their mandrel-bent tubing, thick flanges, and clean welds. They offer both long-tube and shorty designs for many popular applications. Here’s a step-by-step installation approach specific to Flow Master.

Step 1: Prepare the Gaskets and Headers

Apply a thin layer of high-temp anti-seize to the header bolts. If your Flow Master kit includes multi-layer steel (MLS) gaskets, install them dry – they rely on compression to seal. If you are using a softer composite gasket, a very light smear of copper spray-a-gasket can help hold it in position during assembly.

Step 2: Position the Driver’s Side Header

Enter from below the vehicle. Guide the header up into the engine bay, rotating the tubes toward the block. Slide the gasket over the studs (if your head uses studs) or hold it against the ports. Bring the header flange flush to the gasket. Hand-start all bolts finger-tight before tightening any single bolt – this prevents the flange from cocking and damaging the gasket.

Step 3: Tighten to Torque Specifications

Using a torque wrench, tighten bolts in a crisscross pattern from the center outward. Flow Master recommends a torque of 20–25 ft-lb for most applications, but always check the included instructions. Never exceed 30 ft-lb – the flange can distort, and the bolts (often 8 mm) can snap. After reaching the final torque, re-check all bolts after a 10-minute wait.

Step 4: Install the Passenger Side Header

The passenger side often has less clearance due to the starter, A/C compressor, and transmission crossmember. You may need to temporarily unbolt the starter or remove the oil dipstick tube. Slide the header into place from below or above (depending on chassis). Use the same gasket and bolt procedure. For some vehicles, lifting the engine slightly with a jack can provide extra clearance.

Step 5: Reconnect Removed Components

Reinstall the starter (apply anti-seize to its bolts), air intake, throttle body, and any other parts you moved. Double-check that spark plug wires or oxygen sensor wires are routed away from the header tubes – use heat-resistant wire separators or wrap the wires with thermal sleeves. Plug in the O2 sensors (if yours are in the new headers) with anti-seize on the threads, torqued to 30 ft-lb.

Installing Hedman Headers

Hedman headers are popular for their affordability and wide application coverage, especially for classic muscle cars and trucks. Many Hedman headers feature a “Hedman Hustler” series with ceramic coating for heat management. The installation process is similar to Flow Master, but there are nuances.

Step 1: Different Bolt Patterns and Gasket Styles

Hedman often uses a traditional three-bolt pattern at the collector (round flange) rather than a four-bolt. This means you’ll need the correct donut gasket or high-flow collector gasket. Inspect the header ports – some Hedman headers have square ports that do not perfectly match oval head ports; you may need to grind a small amount of material from the port edge for alignment. Always check fitment before final assembly.

Step 2: Installation Sequence for Long-Tube vs. Shorty

For long-tube Hedman headers, always install them from underneath the vehicle. Raise the car high enough to give you room to maneuver. On many trucks, the oil filter may interfere – a remote oil filter relocation kit is a worthwhile upgrade if you plan long-tube headers. Shorty headers typically install from above with less drama.

Step 3: Torque and Retorque

Hedman suggests 18–22 ft-lb for header bolts using a 3/8″ drive torque wrench. Because Hedman flanges are often 3/8″ thick (slightly thinner than competition headers), avoid over-torquing. After the first heat cycle (let the engine warm up to operating temperature and then cool completely), re-torque the bolts. This is critical – the expansion of the header tubes can loosen the bolts. Ignoring this step is the number one cause of later leaks.

Step 4: Collector Connection

Attach the collector to the rest of the exhaust system using the supplied gasket and bolts. Apply anti-seize to the bolts. Do not fully tighten until you have verified the entire exhaust system aligns without binding. Use a flexible exhaust hanger or a slight swivel in the exhaust pipe to avoid stressing the header tubes.

Common Issues and Troubleshooting

Even experienced mechanics encounter problems. Here are solutions to the most frequent headaches.

Header Bolt Keeps Loosening

Use a high-quality locking mechanism such as Stage 8 locking header bolts, which have a crossover clip that prevents rotation. Alternatively, apply a small dab of high-temp threadlocker to the bolts, but be aware that this makes future removal harder.

Gasket Blowout or Leak

A leaking gasket usually results from uneven torque, a dirty surface, or a damaged gasket. Remove the header, inspect the gasket for crushing, and check the head surface for flatness. Use a straightedge across all ports. If the head is warped, you may need a thicker “dead-soft” aluminum gasket that conforms better. Popular choice: Remflex gaskets, which compress to 50% and fill gaps.

Header Tubes Hitting the Steering Shaft

On many Ford and GM vehicles, the steering shaft passes near the driver’s side header. If contact occurs, you can dimple the tube (if mild steel) with a round-ended pry bar. For stainless steel, consider a steering shaft upgrade (collapsible or universal joint type). Never force the header – it can crack.

Broken Exhaust Manifold Bolt

If a bolt broke off in the cylinder head, you have several options: drill out with left-hand drill bits and use an extractor; weld a nut onto the broken stud; or remove the head and have the stud extracted at a machine shop. For stubborn broken bolts in aluminum heads, heat the head around the bolt with a heat gun (not a torch!) and use an extractor carefully.

Excessive Noise After Installation

If the engine sounds much louder than expected, check the collector flange connection – a gap here acts like an open pipe. Also verify that the O2 sensor is properly seated (an air leak in the exhaust stream can cause a loud ticking sound). Finally, ensure nothing is touching the header tubes (like a spark plug wire or brake line) that could cause vibration rattle.

Post-Installation Checks and Break-In

After the headers are fully installed and all components are back in place, perform these checks before starting the engine:

  • Fluid levels – Check coolant and oil. If you disconnected cooling lines or removed the alternator bracket, ensure clamps are tight.
  • Battery reconnected – Reattach the negative terminal. Turn the key to the “on” position without starting, listen for fuel pump priming, and verify the check engine light is not on (if it is, check O2 sensor connections).
  • Initial start – Start the engine and let it idle. Listen for exhaust leaks – a ticking sound that changes with engine speed indicates a gasket leak. Spray a bit of soapy water around the header ports; bubbles reveal leaks.
  • Warm-up cycle – Allow the engine to reach full operating temperature (coolant temp around 195°F). This expands the headers and can cause bolts to loosen. After the engine cools to room temperature, re-torque all header bolts to spec.
  • Test drive – Take a short drive varying engine speed. After returning, check for leaks, check that no wires or hoses are melting against the headers, and listen for metallic rattles. If your check engine light comes on, scan for codes – a lean condition may indicate a vacuum leak or exhaust leak.

Performance Gains and Long-Term Maintenance

Properly installed headers will improve your vehicle’s power output, especially in the mid-to-high RPM range. You should notice a more aggressive exhaust note and quicker engine response. To maintain these gains, follow a few simple rules:

  • Re-torque bolts after the first 500 miles. Thermal cycling can work bolts loose.
  • Inspect for rust. Ceramic-coated headers resist corrosion, but bare steel headers will rust over time. A periodic light coat of high-temp paint or a professional ceramic coating can extend life.
  • Check collector gaskets annually. They see high heat and may deteriorate.
  • Keep the engine tuned. Headers change exhaust flow – you may need to adjust the air/fuel ratio or oxygen sensor placement for optimal performance. A dyno tune is recommended after major exhaust mods.

For more detailed technical information, refer to the manufacturer resources: Flow Master Official Site and Hedman Performance Headers. A comprehensive Summit Racing guide on header fitment basics can also help troubleshoot specific vehicle combinations. For community advice, the ThirdGen.org forum has thousands of header installation threads with real-world tips.

Conclusion: The Rewards of a Well-Executed Header Swap

Installing Flow Master or Hedman headers is a rewarding project that can transform your driving experience. While the process requires patience, the right tools, and attention to detail, the results – more power, better sound, and improved efficiency – are well worth the effort. By following the steps outlined in this guide, cleaning surfaces meticulously, torquing bolts to spec, and rechecking after heat cycles, you can achieve a leak-free installation that performs reliably for years. Remember to enjoy the process and respect safety protocols. Happy wrenching.