Upgrading the exhaust system on a Dodge Charger R/T is one of the most effective ways to unlock additional horsepower, improve throttle response, and give the iconic HEMI a more aggressive tone. Among the most popular modifications is installing Flowmaster High Flow Catalytic Converters. These units reduce exhaust backpressure compared to factory catalytic converters, allowing the engine to breathe more freely. This guide covers everything you need to know, from understanding how high-flow cats work to the exact step-by-step installation process, torque specifications, and common pitfalls to avoid.

What Are High Flow Catalytic Converters and Why Upgrade?

Catalytic converters are emission control devices that convert harmful exhaust gases into less toxic pollutants. Factory catalytic converters on the Charger R/T are designed for low cost and broad compliance but often create significant flow restriction. A high-flow catalytic converter uses a less dense catalyst substrate (often a metallic or ceramic core with fewer cells per square inch) to reduce backpressure while still meeting legal emission standards for most applications.

Benefits for the Dodge Charger R/T 5.7L HEMI

  • Increased horsepower and torque: Expect gains of 10–20 hp and similar torque improvements when paired with a cat-back exhaust or tune.
  • Better exhaust scavenging: Reduced restriction helps the V8 expel gases more efficiently, especially at higher RPM.
  • Deepened exhaust note: High-flow cats produce a sharper, louder sound that complements the HEMI’s rumble.
  • Compatibility with performance headers: If you plan to add long-tube headers, high-flow cats are often required to maintain a street-legal setup.

Important Considerations Before You Start

Before ordering parts, understand your local emissions laws. While Flowmaster’s high-flow catalytic converters are designed to be OBD-II compliant (with proper oxygen sensor placement), they are not legal for use on vehicles that must meet CARB standards unless specifically exempted. Always check your state’s requirements. Additionally, installing high-flow cats may trigger a check engine light if the downstream oxygen sensors read incorrect values; you may need spacer devices or a custom tune to maintain closed-loop operation.

Tools and Materials Needed

Having all the right tools and parts on hand before you lift the car saves frustration and prevents mid-job parts runs. Below is a complete list with notes on why each item matters.

Required Components

  • Flowmaster High Flow Catalytic Converters (kit specific to 2006–2023 Dodge Charger R/T): Confirm the kit includes flanges, gaskets, and pipe sections. Part numbers vary by model year and engine size.
  • Exhaust gaskets (2-inch inlet/outlet, if not included): Always use new gaskets to prevent exhaust leaks.
  • Exhaust clamps (band-style or lap-joint): If the kit uses slip-fit connections.
  • Anti-seize compound (copper-based): Apply to all bolts and threaded connections to prevent seizing from heat cycles.

Tool List

  • Socket and ratchet set (3/8" and 1/2" drive): Metric sockets from 10mm to 21mm cover most exhaust fasteners on the Charger.
  • Combination wrenches (metric): For reaching tight spaces where a ratchet won't fit.
  • Breaker bar (24" or longer): Rusted exhaust bolts often require extra leverage.
  • Penetrating oil (e.g., WD-40 Specialist, PB Blaster, Kroil): Soak all bolts 12–24 hours before removal.
  • Jack and jack stands (3-ton capacity minimum): You need enough lift height to work comfortably under the car.
  • Exhaust pipe cutter or reciprocating saw with metal-cutting blade: On many cars, the factory cats are welded in place, so you may need to cut the pipe.
  • Angle grinder with cut-off wheel: Alternative for cutting through stubborn welds.
  • Exhaust hanger removal tool (optional but helpful): Allows you to unhook rubber hangers without damaging them.
  • Safety glasses and mechanic’s gloves: Rust flakes and hot edges are hazards.
  • Floor jack and axle stands (or ramps): Four jack stands for a stable lift if you need to remove the entire exhaust.
  • Torque wrench (ft-lb): To tighten flange bolts to manufacturer specifications without stripping threads.

If you plan to weld instead of using clamps (recommended for a permanent seal), borrow or rent a MIG welder and have a welding helmet and fire extinguisher nearby.

Preparation Steps

Proper preparation ensures a smooth installation and minimizes the risk of injury. Follow these steps carefully.

Vehicle Position and Safety

  1. Park the Dodge Charger R/T on a level concrete surface. Engage the parking brake and chock the rear wheels.
  2. Disconnect the negative terminal of the battery. This prevents accidental starting and protects the ECU during O2 sensor disconnection.
  3. Allow the exhaust system to cool completely if the vehicle has been driven. Catalytic converters run at 500–900°F; contact can cause severe burns.

Lifting the Vehicle

You need enough clearance to slide under the car and access the full exhaust length. Use a floor jack at the front crossmember jacking point, then place jack stands under the pinch welds (use rubber pads to prevent damage). Lift the rear similarly if you need to remove the entire cat-back section later. Ensure the car is stable before crawling underneath.

Inspect the Existing Exhaust

Spray penetrating oil on every bolt, fastener, and O2 sensor that you will remove. This includes the bolts connecting the catalytic converters to the exhaust manifolds/headers and the bolts at the junction to the mid-pipe. While the oil soaks, inspect the rubber hangers for cracks or wear. If any hangers are brittle, replace them now to avoid breaking during the installation.

Removing the Old Catalytic Converters

On most Dodge Charger R/T models, the catalytic converters are located directly behind the exhaust manifolds, one per cylinder bank. The easiest removal method depends on whether your car has flanged or welded connections. Factory Charger R/Ts often have flanged connections at the manifold but welded connections near the resonator or mid-pipe. We cover both scenarios.

Step 1: Remove Downstream Oxygen Sensors

Use an O2 sensor socket (22mm) to unthread the downstream sensors from the catalytic converters. Do not damage the wiring. Place the sensors in a clean location—you will reinstall them into the new converters unless you are using include bungs that are already threaded. If the sensors are stuck, apply more penetrating oil and carefully use a wrench. Heat from the car can help; run the engine briefly (if safe) to warm the metal, but be cautious of hot exhaust.

Step 2: Unbolt the Converters from the Manifolds

Locate the flange bolts connecting each converter to the exhaust manifold. Use a socket and ratchet with a breaker bar. If bolts are rusted, apply heat with a propane torch (if safe) to break the bond. Remove the bolts and any integrated spring bolts. On some years, the manifold-to-converter connection uses a donut gasket—inspect it and replace if damaged.

Step 3: Cut or Unbolt the Rear End of the Converters

If the converter outlet pipe is welded to the mid-pipe (common), you will need to cut the pipe. Use a reciprocating saw with a 10-inch bi-metal blade or an angle grinder. Measure carefully: cut about 1–2 inches behind the converter body so you have enough pipe length to attach the new converter. If the connection is flanged, simply unbolt it. For the best seal later, ensure the cut is square.

Step 4: Remove the Converters

Work each converter out from the bottom of the car. You may need to drop the exhaust slightly by unhooking the rubber hangers. Loosen the hangers at the rear of the mid-pipe to give a few inches of movement. If the converter is stuck on hangers, use a pick to release the rubber grommets. Remove the old gaskets and inspect the manifold flanges for warping or cracks.

Installing the Flowmaster High Flow Catalytic Converters

With the old cats removed, you can now install the Flowmaster units. Follow the instructions included with your kit, but the general process is below.

Step 1: Dry Fit the New Converters

Position each converter into place without tightening anything. Check that the inlet flange aligns with the manifold outlet and that the outlet pipe aligns with the existing mid-pipe. If the pipe connections are slip-fit, slide the converter onto the mid-pipe far enough to ensure a 2–3 inch overlap. Use the supplied clamp to mark where the clamp will sit. If the kit requires welding, mark the overlap with a paint pen.

Step 2: Install New Gaskets and Apply Anti-Seize

Place new gaskets on the manifold flanges. Apply a thin layer of anti-seize to the threads of all bolts and nuts. This prevents galling and makes future removal easier. For slip-fit connections, apply a small amount of exhaust system sealant to the pipe joint (optional—many choose to rely on clamps only).

Step 3: Bolt the Converters to the Manifolds

Thread the bolts (or studs with nuts) through the flanges. Tighten evenly in a star pattern. Torque to the manufacturer’s specification: typically 25–35 ft-lb for 10mm bolts, but check your kit. Over-tightening can warp the flange or strip threads.

Step 4: Secure the Outlet Connections

If using clamps: position the clamp over the slip joint, then tighten the clamp to 30–40 ft-lb, depending on clamp size. Do not overtighten or you may crush the pipe. If welding: tack weld the joint in a few spots, then remove the converter to finish welding the full seam (to avoid heat damage to the catalyst). A continuous weld is best for preventing leaks. After welding, allow the weld to cool before reinstallation.

Step 5: Reattach Hangers and Reconnect Oxygen Sensors

Rehook the rubber hangers to support the exhaust. Reinstall the downstream O2 sensors into the new converters’ bungs. Apply a small amount of anti-seize to the sensor threads (not the sensor tip). Tighten to 25–30 ft-lb. For upstream sensors (if they were removed), reinstall them into the manifold bungs.

If your new converters have different O2 sensor port placement than stock, you may need O2 sensor extensions or spacer devices (often called “defoulers”). These help push the sensor out of the direct exhaust stream to avoid a rich/lean code. Many Flowmaster kits include angled bungs to position sensors appropriately, but verify before finalizing.

Reconnecting the Exhaust System

Once both converters are installed, reconnect any sections of the exhaust you disassembled. For a simple cat upgrade, this typically means reconnecting the mid-pipe to the converters and then to the cat-back system (if removed). Ensure the mid-pipe hanger is seated correctly. Tighten all remaining flange bolts and clamps.

Final Checks Under the Car

  • Verify that no part of the exhaust contacts the underbody, frame, or driveline. Clearance should be at least 1 inch everywhere.
  • Check that O2 sensor wires are not routed near hot pipes or moving components. Use zip ties to secure loose wiring.
  • Hand-tighten all clamps and bolts one last time; use the torque wrench on critical fasteners.

Testing and Post-Installation Steps

Before lowering the car, perform a preliminary leak check.

Leak Detection

  1. With the car still on jack stands, start the engine. Listen for hissing, ticking, or exhaust pulses at every joint. Use a rag or paper towel to feel for leaks—your hand will sense puffs of exhaust air.
  2. If you hear a leak, pinpoint the location. Common leak points include manifold flanges and slip joints. Tighten clamps slightly more (do not exceed clamp rating) or re-torque flange bolts.
  3. For stubborn leaks, use a can of smoke test fluid or a soapy water spray (bubbles will appear at leak points).

Cold Start and O2 Sensor Operation

The engine may run a bit rough initially as the oxygen sensors recalibrate. Let the engine idle until it reaches operating temperature (fan comes on). Monitor the check engine light: if it stays on, read the codes with an OBD-II scanner. Common codes (P0420, P0430) indicate catalytic converter efficiency below threshold. This can happen if the downstream sensors are not receiving the correct airflow or if the cats need to heat up. Drive the car for 30–50 miles to allow the ECU to relearn. If the light persists, you may need a spacer on the downstream sensors or a custom ECM tune.

Test Drive

  1. Lower the vehicle and remove jack stands.
  2. Take the car for a gentle 15-minute drive, varying RPMs. Listen for changes in exhaust tone and any rattles.
  3. Accelerate moderately and let off the throttle to check for drone or vibration. The Flowmaster high-flow cats should produce a deeper note without excessive cabin drone.
  4. After the drive, park on level ground and check for any new leaks or loose hardware as the system cools.

Maintenance and Long-Term Care

High-flow catalytic converters require no regular maintenance, but you should inspect the system annually:

  • Check for rust, especially at clamp areas and welds.
  • Listen for rattling (a sign of internal catalyst degradation).
  • Re-torque flange bolts after the first heat cycle (100 miles).
  • If you drive in severe weather, consider applying a high-temperature anti-corrosion coating to the converters and pipes.

Additional Resources

For more information on Dodge Charger R/T exhaust upgrades, consult Flowmaster’s official website for part compatibility and technical support. For community insights and install tips, visit dedicated forums such as Charger Forumz. To understand emission legalities, review the EPA guidelines on aftermarket catalytic converters.

Conclusion

Installing Flowmaster High Flow Catalytic Converters on your Dodge Charger R/T is a rewarding upgrade that improves both performance and sound. By following this detailed guide, you can complete the installation in a single day with basic mechanical skills. The key to success lies in thorough preparation, careful removal of rusted fasteners, and ensuring leak-free connections. Once done, you will immediately notice a freer-revving HEMI and a more aggressive exhaust note. For maximum gains, pair the high-flow cats with a cold air intake and a professional dyno tune. Enjoy the open road with your enhanced Charger R/T.