3.5” High-Flow Stainless Downpipe for 2004.5+ Duramax 6.6L (LLY/LBZ/LMM/LML/L5P)
Upgrade your Duramax exhaust system with SPETUNER’s high-flow 3.5” downpipe, designed to maximize performance on all 2004.5+ Chevrolet and GMC 2500HD/3500HD diesel trucks. Crafted from durable stainless steel, this turbo downpipe delivers faster spool-up, reduced backpressure, and cooler exhaust gas temperatures—ideal for tuned and deleted builds.
Fitment:
| Year |
Make |
Engine |
| 2004.5–2010 |
Chevrolet/GMC 2500HD/3500HD |
LLY / LBZ / LMM |
| 2011–2016 |
Chevrolet/GMC 2500HD/3500HD |
LML |
| 2017+ |
Chevrolet/GMC 2500HD/3500HD |
L5P |
Will not fit cab and chassis trucks.
Key Features
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Mandrel-bent 3.5” tubing for optimal exhaust flow
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Material: for 2004.5-2016 models, use 201 stainless steel, for 2017+ models, use 409 stainless steel – strength + cost efficiency
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Direct bolt-on installation – no modifications needed
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Compatible with most EGR/DPF delete kits
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Supports higher boost and tuned diesel applications
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Optional ceramic coating for enhanced heat control
Why 409 Stainless Steel?
409 stainless steel offers exceptional durability and heat resistance, making it ideal for high-performance diesel exhaust systems. It provides better longevity than aluminized steel, at a more affordable price than 304 stainless.
Performance Benefits
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Faster turbo response
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Lower exhaust gas temperatures (EGTs)
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Increased exhaust velocity
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Gains in horsepower and torque
What does a downpipe do?
The downpipe channels exhaust gases from the turbo into the exhaust system. A restrictive factory downpipe creates a bottleneck, especially after tuning. Upgrading to a high-flow downpipe improves:
Why Choose SPETUNER?
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North American Duramax experts
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Fast shipping from USA & Canada
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Premium materials, performance-tested parts
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Trusted by 10,000+ diesel enthusiasts