Downpipe GM Duramax Diesel L5P 6.6L 2017-2023 3.5 inches

An aftermarket downpipe for the GM Duramax L5P 6.6L diesel engine (2017-2023 Silverado/Sierra 2500/3500 HD). Here’s a detailed breakdown:

Key Features & Benefits:

1. Fitment:

• 2017–2023 Chevrolet Silverado 2500/3500 HD

• 2017–2023 GMC Sierra 2500/3500 HD

• Not compatible with Cab & Chassis models (different exhaust routing).

2. Performance Gains:

• 3.5-inch diameter (vs. restrictive stock downpipe)

• Reduces turbo backpressure, allowing the turbo to spool faster and more efficiently.

• Increases horsepower & torque, especially when paired with a tune.

• Better exhaust flow improves throttle response and reduces EGTs (Exhaust Gas Temperatures).

3. Construction & Design:

• Mandrel-bent tubing for smooth airflow.

• Options available:

  • High-flow catalytic converter (retains some emissions compliance but improves flow).

  • Cat-less (straight pipe) – Maximizes performance but illegal for on-road use.

4. Installation:

• Replaces the restrictive factory downpipe (which often has a small diameter and restrictive catalytic converter).

• May require minor modifications depending on the kit (some are bolt-on).

• Tuning recommended to fully optimize performance (since reduced backpressure can affect turbo efficiency).

Legal & Warranty Considerations:

⚠️ Important:

• EPA & Emissions Compliance:

  • Removing or modifying the catalytic converter is federally illegal for on-road vehicles (Clean Air Act violations).

  • Fines for tampering can be severe (up to $4,819 per violation for individuals, more for shops).

  • Some states (like California) have strict inspections (SMOG checks) that will fail a deleted truck.

• Warranty Impact:

  • GM may void powertrain warranty if they detect aftermarket downpipe modifications.

Alternatives (For Legal Use):

If you need better flow without legal risks, consider:
✔ High-flow catted downpipe – Improves performance while keeping emissions legal.
✔ Factory-style replacement – Less restrictive than stock but still compliant.
✔ Full turbo-back exhaust system – Includes a high-flow downpipe but retains emissions equipment.

Final Thoughts:

• For max performance (off-road/racing): A cat-less downpipe + tune will deliver the biggest gains.

• For street use: A high-flow catted downpipe is the safer choice.

• Always check local laws before deleting emissions components.

Would you like recommendations on specific brands or tuning options?