3.5'' Downpipe Exhaust For 2017-2025 L5P 6.6L Duramax Diesel | SPELAB

The downpipe on your turbocharged vehicle is directing the exhaust gases out of the turbine housing into the exhaust system. An aftermarket downpipe will typically be larger in diameter and either uses a high-flowing catalytic converter or remove the catalytic converter altogether.

By removing the factory downpipe and replacing it with a high flowing unit you are allowing the turbo to more efficiently move gases away from the turbine which creates more power. Since the factory restrictions are now gone you can increase the boost on the vehicle as the factory downpipe is a choking point for performance.

Key Features

• • 3.5-Inch Large Diameter Design: Features a larger internal diameter than the stock pipe for dramatically increased exhaust flow, reducing turbo lag and enhancing throttle response.
  • Turbo Efficiency Optimization: Accelerates exhaust gas exit from the turbine housing, minimizing backpressure to allow the turbo to spin faster and produce more boost and power.
  • Eliminates Factory Restriction: Directly replaces the restrictive OEM downpipe, solving the exhaust choking point and providing the essential foundation for further performance mods (e.g., tuning, increasing boost levels).
  • Precision Fit and Durability: Constructed from high-quality stainless steel for superior corrosion resistance and long-term reliability under extreme heat.

Product Specifications

• Engine: GM Duramax 6.6L L5P Turbo-Diesel
• Pipe Diameter: 3.5 inch
• Material: Stainless Steel
• Surface: Mirror Polish (raw 304 SS)
• Configuration: Catless
• Flange Type: Bolt-on (4-Bolt) turbo outlet + V-Band clamp
• Weight: 4.10 kg (4100 g)

What's Included

• Downpipe
• Gasket(s)
• V-Band clamp(s)
• O2 sensor bung(s)
• Mounting hardware

Check Before Choosing

• Cab & Chassis exclusion: Will NOT fit Cab & Chassis trucks — only fits pickup models.
• Tune recommended for delete: Yes — a diesel tune is required to clear the CEL/DPF codes and safely manage the increased flow.
• Silver vs Black: Silver is the SPELAB "Best Seller" — exceptional value and time-tested reliability. Black ceramic is premium look with extra heat management.
• Street legality: No — not CARB or EPA certified. Off-road / competition use only.

Vehicle Fitment

Compatible vehicles: Chevrolet Silverado 2500HD, GMC Sierra 2500HD, Chevrolet Silverado 3500HD, and GMC Sierra 3500HD (2017–2025). Will NOT fit Cab & Chassis trucks.

If you would like to purchase the black version, please click the link

Installation Guide

Pre-Installation Checklist

• Confirm your engine code and model year match the fitment list above
• New gaskets and mounting hardware ready
• 22mm slotted O2 sensor socket + PB Blaster on hand
• a diesel tune to clear CEL and DPF codes

Installation Steps

1. Lift the vehicle and secure it on jack stands
2. Soak the O2 sensors and flange bolts with PB Blaster for 30+ minutes
3. Unplug and remove the O2 sensors with the slotted socket
4. Remove the factory downpipe and discard the old gasket
5. Bolt on the new downpipe with a fresh gasket
6. Reinstall and reconnect the O2 sensors
7. Flash your tune to suppress the check engine light

Installation Notes

• Never reuse the old gasket — it will cause an exhaust leak
• Use a slotted O2 socket, not a wrench — the sensor threads strip easily
• A catless downpipe triggers a CEL until the ECU is tuned
• Expect a stronger raw exhaust smell (normal for catless)

FAQ

Does it fit Cab & Chassis trucks?

No — this SKU is for pickup models only.

Silver or Black?

Both fit the same applications — Silver is the time-tested best-value choice; Black is premium with ceramic heat management.

Do I need a tune on the L5P?

Yes — a diesel tune is required to clear the CEL/DPF codes and safely manage increased flow.

Is it street-legal?

No — not CARB or EPA certified. Off-road / competition use only.