.4 HEMI Headers Install Guide: Improving Power and Sound on a 2018+ Dodge Charger or Challenger

The 2018+ Dodge Charger and Challenger equipped with the 6.4L naturally aspirated HEMI (392) engine deliver a formidable blend of muscle, style, and daily-driver capability. While the factory exhaust system is tuned for noise compliance and cost efficiency, it leaves measurable performance on the table. Installing aftermarket long-tube or shorty headers is one of the most rewarding modifications you can make. This guide covers the why, the how, and what to expect when upgrading headers on your SRT, Scat Pack, or R/T model, including critical installation steps, tuning considerations, and safety practices.

Why Upgrade to .4 HEMI Headers?

Factory exhaust manifolds on the 6.4L HEMI are heavy, restrictive cast-iron pieces. They dampen airflow, trap heat, and create a muted exhaust note. Upgrading to aftermarket headers brings multiple measurable benefits:

  • Increased Horsepower and Torque: By reducing backpressure and improving scavenging, headers can free 15–30 hp (and similar torque) at the wheels, with the largest gains in the mid-to-high rpm range. Long-tube headers generally produce more peak power, while shorties offer easier installation and maintain smog compliance in most states.
  • Enhanced Sound Character: A free-flowing header changes the exhaust note from a deep hum to a sharper, more aggressive bark, especially above 3,500 rpm. Paired with a cat-back or axle-back system, the result is a clean, muscular sound that turns heads without being obnoxious on the highway.
  • Improved Thermal Management: Headers, especially those with ceramic coatings, reduce underhood temperatures. The 6.4L HEMI runs hot, and cooler intake air temperatures can help maintain consistent power output during extended runs at the track or on mountain roads.
  • Moderate Fuel Economy Gains: While not the primary motivation, improved exhaust efficiency — when combined with a proper tune — can yield 1–2 mpg improvement under steady cruising conditions.

Header Options for the 6.4L HEMI

Before you buy, decide between two primary header designs:

Long-Tube Headers

Long-tube headers replace the entire manifold and extend the primary tubes down to the collector, often eliminating the factory catalytic converters or requiring a high-flow cat setup. They offer the largest power gains (especially above 4,000 rpm) and the most aggressive sound. However, installation is more labor-intensive (lifting the engine or dropping the K-member may be required), and they are not legal on vehicles that require CARB approval unless you retain cats and have a tune that supports them.

Shorty Headers

Shorty headers (also called “short tube” or “bolt-on” headers) are a direct replacement for the factory manifolds, mounting the collector in approximately the same position as the stock outlet. Power gains are smaller (5–12 hp), but installation is far simpler — often doable in a home garage with basic tools. Shorties also keep the factory catalytic converters in their stock location, making them street-legal in all 50 states. They are an excellent first step for enthusiasts who want improved sound and a modest power bump without major drivetrain disassembly.

Popular brands for 6.4L HEMI headers include Kooks, American Racing Headers, Borla, and Stainless Works. Choose 304 stainless steel for longevity and corrosion resistance; ceramic-coated mild steel can be cheaper but is more prone to rust.

Tools and Materials Needed

Completing a header swap on a 2018+ Charger or Challenger requires the right equipment. Below is a comprehensive list. Make sure you have everything within reach before starting.

  • Socket set (standard and deep sockets, 3/8″ and 1/2″ drive) – sizes 8, 10, 13, 15, 18, 21 mm are common
  • Wrench set (combination wrenches up to 21 mm, plus a ratcheting wrench for tight spots)
  • Torque wrench (1/2″ drive, 0–100 ft-lb range)
  • Jack and jack stands (2-ton capacity minimum; four stands recommended for stability)
  • Header gaskets (check manufacturer recommendation; many include gaskets with the headers)
  • New header bolts (often included, but quality aftermarket hardware is worth the extra cost)
  • Oxygen sensor socket (7/8″ or 22 mm for the wideband O2 sensors)
  • Penetrating oil (such as Kroil or PB Blaster) for stubborn bolts
  • Safety glasses and gloves
  • Shop rags and a vacuum to clean debris from the engine bay
  • Optional but helpful: Die grinder with a carbide burr for trimming any clearance issues, and an engine support bar if removing the K-member

Step-by-Step Installation Process

This procedure is written assuming you are installing shorty headers, which do not require lifting the engine or removing the K-member. For long-tube headers, additional steps (such as removing the front sway bar and motor mounts) will be necessary. Consult your header kit’s specific instructions.

1. Prepare Your Vehicle

Park the car on a flat, level surface. Disconnect the negative battery terminal and let the engine cool completely — the exhaust manifolds get extremely hot. Jack up the front of the vehicle using the factory lift points, then place jack stands under the frame rails or the front subframe. Chock the rear wheels. For extra clearance, consider removing the front wheels.

2. Remove the Old Exhaust Manifolds

Start by unplugging the oxygen sensors from their connectors (typically located near the top of the engine, behind the valve covers). Remove the O2 sensors from the manifolds using the O2 socket — careful not to damage the threads. Next, remove the bolts that hold the exhaust pipes to the manifold flanges; there are usually two spring-loaded bolts per side. With the exhaust pipes free, unbolt the heat shield (if your car has one) and then remove the manifold bolts. On the 6.4L, the manifold bolts are notoriously tight and prone to corrosion. Soak them with penetrating oil 30 minutes beforehand. Use a breaker bar if needed. On the driver’s side, you may need to disconnect the steering shaft intermediate shaft to access the rear manifold bolt — mark its alignment before removal. On the passenger side, the A/C line bracket may need to be unbolted. Carefully pull each manifold straight out; if it sticks, gently tap it with a rubber mallet. Clean the block mounting surface with a gasket scraper and shop rags.

3. Install the New Headers

Apply a thin bead of high-temp RTV or copper spray to the new header gaskets (if not pre-coated). Place the gaskets over the exhaust ports, aligning the bolt holes. Some headers come with a gasket that fits into a recess — follow the kit instructions. Offer up the header from below the car. For shorties, you can slide them into position with the engine still in the stock location. For long-tubes, you may need to remove the motor mount bolts and jack up the engine about 2 inches to clear the tubes. Hand-thread all the header bolts into the heads, then start tightening from the center ports outward, working in a cross pattern. Torque to the manufacturer’s specification (typically 15–20 ft-lb for the header bolts; do not overtighten or you will strip the aluminum heads). Reinstall any brackets that were removed (heat shield, A/C bracket, steering shaft). Attach the O2 sensors to the header bungs. If your kit has them, install the spark plug wire looms that hold the wires away from the header tubes.

4. Reattach the Exhaust System

Lower the car enough to access the exhaust system. For shorty headers, you simply bolt the factory Y-pipe or mid-pipe back onto the header collectors using a new gasket. For long-tubes, you will need to connect the high-flow catalytic converters or a full custom exhaust. Ensure all V-band clamps or flange bolts are torqued to spec. Use anti-seize on all bolts that will be exposed to heat.

5. Reconnect the Battery and Test

Once everything is connected (including O2 sensors), reconnect the battery. Start the engine and let it idle. Listen for exhaust leaks — a ticking sound often indicates a leak at the header-to-head gasket. Re-torque the header bolts after the engine has gone through one heat cycle (run it to operating temperature, let it cool, then re-check torque). Also check for any contact between the header tubes and the chassis, steering shaft, or brake lines. Address any interference immediately.

Post-Installation Tuning and Tuning Considerations

After installing headers, your vehicle’s air-fuel ratio, timing, and throttle response will change. The factory ECU can compensate to some degree via adaptive fuel trims, but for maximum gains and safe operation, a custom tune is highly recommended. A tuner can adjust for the removed catalytic converters (in states where that is legal), increase spark advance, and dial in the wideband O2 sensors. Even with shorty headers, a tune will unlock 5–10 additional horsepower beyond the bolt-on gain.

Popular tuning platforms for the 6.4L HEMI include HP Tuners and DiabloSport. Many shops offer remote tuning via email after you log data. Be aware that removing catalytic converters is illegal in many jurisdictions and can trigger a check engine light (CEL) for catalyst inefficiency. A tune can disable the associated codes, but that does not make the car legal for on-road use. Consult your local laws before choosing long-tube headers.

Common Issues and Troubleshooting

  • Exhaust Leaks: The most common post-install issue. A puffing or ticking sound under acceleration. Solutions: re-torque bolts, replace gaskets with thicker multi-layer steel gaskets, or check for header warping.
  • Header-to-Body Clearance: Long-tube headers on the passenger side often contact the bellhousing or the K-member. Use a grinder for minor clearance, or purchase a set of offset header bolts that allow you to tilt the collector away from the block.
  • Check Engine Light (CEL): Usually caused by O2 sensor readings that fall outside the expected range (lean/rich codes or catalyst efficiency). This almost always requires tuning or installing spark plug non-foulers to move the downstream O2 sensor out of the exhaust stream (illegal for on-road use in many areas).
  • Difficulty Reaching Bolts: The rear bolt on the driver’s side is notoriously tight. Use a flexible socket extension or a universal joint socket. If the bolt snaps, you will need to use a bolt extractor. Always use anti-seize on reinstallation.

Summary and Final Advice

Installing headers on your 2018+ Dodge Charger or Challenger with the 6.4L HEMI is one of the most rewarding upgrades for power and sound. Shorty headers offer an excellent entry point with moderate gains and easier installation, while long-tube headers deliver maximum performance for those who plan to tune and track their vehicles. Whichever route you take, careful preparation, quality components, and a post-install tune will ensure you get the most out of your investment.

Always refer to the manufacturer’s instructions for your specific header kit and vehicle year. If you are not confident in your mechanical ability, a professional installation from a reputable speed shop is money well spent. With the right approach, you will enjoy a stronger, better-sounding HEMI that stands out from the crowd.