3.5'' Downpipe Exhaust For 2017-2024 L5P 6.6L Duramax Diesel Black| SPELAB

This 3.5" turbocharger downpipe will increase exhaust flow, improving performance.  

Made with mandrel-bent 3.5-inch stainless steel tubing and coated in a ceramic black finish, this SPELAB high-performance L5P downpipe significantly improves airflow, reduces EGTs, and enhances turbocharger response. It’s the ideal component to begin building a full L5P Duramax downpipe delete system.

Whether you're replacing a restrictive stock pipe or upgrading for tuning purposes, this Duramax downpipe delivers the gains you expect in both performance and durability.

Specifications

Application:  Downpipe Exhaust
Material: Stainless Steel
Surface: Mirror Polish

Key Features

• Complete Kit: Includes downpipe, heat wrap, clamps, and precision flanges
• Superior Heat Control: Minimizes heat soak and improves turbo efficiency
• Direct Fit: Designed to replace the 2018 L5P downpipe without cutting or welding
• Ceramic Coating: Sleek finish with high resistance to corrosion and heat

OE vs. SPELAB Downpipe Comparison

What's the Difference Between a Downpipe and an Exhaust?

Upgrading the downpipe = performance and throttle response
Upgrading the exhaust = tone, flow, and backpressure control

• 2017-2024 Chevrolet Silverado & GMC Sierra 2500 & 3500HD 6.6L Duramax pickup trucks.
• Will not fit Cab & Chassis trucks.

What does a downpipe do?

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.

Q1: Is this SPELAB downpipe catless or catted?
A: This is a catless downpipe, meaning it does not contain a catalytic converter. It’s designed for maximum exhaust flow and performance—ideal for off-road and race-use L5P Duramax downpipe delete builds.

Q2: What is the difference between a catted and a catless downpipe?
A: A catted downpipe includes a high-flow catalytic converter and is more emissions-friendly, while a catless downpipe removes restrictions completely for maximum performance. SPELAB’s 3.5-inch downpipe is catless.

Q3: Do I need a tuner after installing this downpipe?
A: If you’re using it as part of an L5P downpipe delete or DPF removal system, a tuner is required to prevent check engine lights and optimize performance.

Q4: Which model years does this downpipe fit?
A: It fits all 2017–2024 L5P 6.6L Duramax trucks, including those needing a 2018 L5P downpipe replacement.

Q5: Can this downpipe work with the stock exhaust?
A: Yes, it is compatible with both OEM mid/tail sections and aftermarket 4” or 5” Duramax exhaust systems.

Q6: Does installation require cutting or welding?
A: No cutting or welding is needed. This is a bolt-on L5P Duramax downpipe that uses factory-style mounting points and flange connections.

Q7: Will this downpipe change my exhaust sound?
A: Slightly. It deepens the tone and improves airflow. Paired with a full exhaust upgrade, the sound becomes much more aggressive.

Q8: What’s the wall thickness and corrosion resistance like?
A: Made from thick 2mm stainless steel with ceramic coating, it provides excellent heat and corrosion resistance in all weather conditions.

Q9: Can I use this as part of a DPF delete system?
A: Yes. It’s commonly used in L5P Duramax downpipe delete setups as the first step in removing stock emissions restrictions. Off-road use only.

Q10: Who should buy this 3.5-inch downpipe from SPELAB?
A: It’s perfect for diesel enthusiasts looking to increase power, reduce turbo lag, and build a performance-tuned L5P truck for off-road or race use.