Flashark 3.5'' Downpipe Exhaust For 2017-2023 Chevy/GMC Silverado/ Sierra L5P Duramax Diesel 6.6L
The factory downpipe on your L5P 6.6L Duramax is a bottleneck — small diameter, crushed bends, and a restrictive DOC (Diesel Oxidation Catalyst) housing choke the turbo's ability to exhale. The Flashark 3.5" Catless Downpipe eliminates that restriction with a full mandrel-bent T-304 stainless steel flow path, reducing turbo backpressure and improving spool response for 2017-2023 Silverado/Sierra 2500HD/3500HD trucks.
Unlock the full potential of your L5P Duramax 6.6L engine with the Flashark 3.5" Downpipe Exhaust. Designed specifically for the 2017-2023 Chevy and GMC models, this high-flow downpipe improves exhaust flow, reduces turbo lag, and increases horsepower. Made from durable stainless steel with a mirror-polished finish, it optimizes turbocharger efficiency and boosts engine performance. Perfect for those looking to enhance the power, responsiveness, and overall driving experience of their L5P Duramax 6.6L. Whether you're towing or racing, this downpipe is the ideal upgrade for your engine.
⚠️ This is a Catless, off-road-only product. A custom ECM delete tune (PPEI, EZ-Lynk, or DuramaxTuner) is mandatory — stock programming will throw persistent CEL codes and trigger limp-home mode. Expected gains: 15-25 whp with delete tune (downpipe alone), up to 50-100+ whp with full delete package + aggressive tune. Heat wrap included to reduce under-hood radiant heat. Will NOT fit Cab & Chassis models.
Key Features
Catless Design — Maximum Unrestricted Flow — Removes factory DOC restriction from the downpipe section for the highest possible exhaust throughput; ideal for competition trucks running full delete tunes
3.5" Mandrel-Bent T-304 Stainless Steel — 20% greater flow area vs. stock crushed-bend pipe while maintaining optimal exhaust gas velocity for turbo spool on builds under 700 HP
Heat Wrap Included — Lower Engine Bay Temps — Premium fiberglass heat wrap reduces under-hood radiant heat by up to 50%, protecting wiring, intercooler piping, and turbo actuator
4-Bolt Turbo Flange with Pre-Installed Studs — Direct bolt-on to the L5P turbo outlet housing; no welding or adapter required
Requires ECM Delete Tune — Diesel-specific tune (PPEI, EZ-Lynk, or DuramaxTuner) must be installed BEFORE or alongside this downpipe; stock ECM will throw CEL, trigger limp-home mode, and reduce power
Package Includes
1x 3.5" Catless Downpipe
1x Fiberglass Heat Wrap
2x Stainless Steel Clamps
What Does the Downpipe Do for Your L5P Duramax 6.6L Engine?
The downpipe is a critical part of your Duramax 6.6L diesel engine, responsible for channeling exhaust gases from the turbocharger turbine housing into the exhaust system. When upgraded, the downpipe typically features a larger diameter than the factory version, which improves exhaust flow. Some high-performance versions also replace or eliminate the catalytic converter for even better efficiency.
By swapping out the factory downpipe for a high-flow option, you allow your engine to expel exhaust gases more efficiently, reducing turbo lag and increasing horsepower. The stock downpipe can act as a bottleneck, restricting exhaust flow and limiting engine performance. An upgraded L5P downpipe removes this restriction, enabling quicker turbo spool, higher boost levels, and ultimately unlocking more power from your Duramax diesel engine.
Why Choose the Flashark Downpipe?
If you’re looking for a complete, high-performance downpipe for your L5P Duramax 6.6L, the Flashark 3.5" Downpipe is the clear choice. Designed specifically for 2017-2023 Chevy and GMC Silverado and Sierra 2500/3500HD trucks, this kit improves exhaust flow, reduces turbo lag, and increases horsepower—without any extra modifications or tuning.
Whether you call it the Flashark Downpipe, the 3.5" high-flow exhaust, or simply a reliable Duramax performance upgrade, this all-in-one kit is engineered for maximum turbo efficiency, easy installation, and lasting durability, while maintaining compatibility with your emissions system.
What is the L5P Duramax 6.6L Engine?
The L5P Duramax is a turbocharged diesel engine introduced by GM for their 2017-2023 Chevy and GMC trucks. Known for its impressive power output of up to 445 horsepower and 910 lb-ft of torque, the L5P engine is a significant upgrade over its predecessors. With improved fuel efficiency, enhanced emissions control, and a more robust design, the L5P provides optimal performance for both everyday driving and heavy-duty applications. The engine also features advanced turbocharging technology that benefits greatly from high-flow aftermarket components, such as the Flashark Downpipe.
| Years |
Make |
Model |
Engine |
| 2017-2023 |
Chevrolet |
Silverado 2500HD / 3500HD |
L5P Duramax 6.6L V8 Diesel |
| 2017-2023 |
GMC |
Sierra 2500HD / 3500HD |
L5P Duramax 6.6L V8 Diesel |
Q: What trucks does this L5P downpipe fit?
A: This Catless downpipe is designed exclusively for 2017-2023 Chevrolet Silverado 2500HD/3500HD and GMC Sierra 2500HD/3500HD equipped with the L5P Duramax 6.6L V8 diesel engine. The L5P was introduced in the 2017 model year and carries through 2023 for HD pickup trucks. It will NOT fit: 2016 or earlier Duramax (LML, LMM, LB7, LBZ, LLY — completely different turbo architecture), 2024+ HD trucks (turbo/downpipe configuration may have changed — verify before ordering), Cab & Chassis models (different turbo housing and downpipe interface), or 1500-series Silverado/Sierra. Check your door jamb sticker for the RPO code L5P before ordering.
Q: Do I need a tune after installing this Catless downpipe?
A: Yes — a tune is mandatory, not optional. The factory ECM monitors DOC/DPF pressure differential sensors as part of exhaust backpressure parameters. When you remove emissions equipment with a Catless downpipe, the ECM will throw persistent check engine lights (CEL), trigger limp-home mode (reduced power, limited RPM), and attempt to "protect" the engine by derating performance. A quality delete tune from PPEI, EZ-Lynk, or DuramaxTuner will recalibrate fueling maps, disable emissions monitors, and allow the ECM to properly manage the modified exhaust system. Do not install this downpipe without budgeting for a tune — it's part of the total cost of ownership.
Q: How much power does this Catless downpipe add?
A: Power gains depend on your complete setup:
- Downpipe only + delete tune: ~15-25 whp / 30-50 lb-ft torque — primarily improved mid-range spool response and throttle feel
- Full delete package (downpipe + DPF delete + EGR delete + aggressive tune): ~50-100+ whp / 100-150+ lb-ft torque — these larger numbers reflect the entire system working together
The downpipe alone is not a magic power adder — it removes the restriction so the turbo can breathe, but the tune is what actually unlocks the fueling and boost to capitalize on that improved flow. Stacking downpipe + DPF delete + EGR delete + tune = the real power package.
Q: Is this Catless downpipe street legal?
A: No. This product is for off-road and competition use only. Removing the DOC (Diesel Oxidation Catalyst) and/or DPF from a highway-registered vehicle violates the Clean Air Act (42 U.S.C. § 7412). States that follow CARB standards (California, New York, Colorado, etc.) are especially strict — you risk EPA civil fines (up to $44,539 per violation), state inspection failures, a voided powertrain warranty, and potential criminal penalties for repeat offenders. This Catless downpipe is designed for race trucks, competition vehicles, and trucks registered in jurisdictions without emissions testing. If you daily-drive and need to pass inspections, this product is NOT for you.
Q: What's the difference between a 3.5" and 4" downpipe for the L5P?
A: The 3.5" is the optimal choice for 95% of L5P owners:
- 3.5" — Balances significantly increased flow with maintained exhaust gas velocity for proper turbo spool. Ideal for builds from stock to ~650 HP. This is what most tuners recommend.
- 4" — Maximum flow capacity for heavily modified trucks pushing 700+ HP with upgraded injectors, larger turbo, and aggressive fueling. On moderate builds, 4" can actually hurt spool because exhaust gas velocity drops too low.
Rule of thumb: If you're not planning a 700+ HP build, stick with 3.5". Bigger isn't always better for turbo response.
Q: What does "DPF delete" mean, and why do people do it?
A: DPF = Diesel Particulate Filter, a honeycomb ceramic filter that captures exhaust soot. It regenerates periodically by burning off accumulated particulate at high temperatures. Common reasons for DPF deletion: Clogged/failed DPF (replacement costs $2,000+; delete eliminates the failure point), Better fuel economy (reduced exhaust restriction means the engine works less hard), More power (DPF creates significant backpressure that limits turbo efficiency), No regeneration cycles (eliminates the fuel-wasting regen process). Trade-offs: You lose emissions compliance, void the powertrain warranty, and cannot register the vehicle in emissions-testing states. DPF delete is only legal for off-road/competition vehicles.
Q: Will this Catless downpipe void my Duramax warranty?
A: Almost certainly, yes. GM can and will deny warranty claims related to any failure they determine was caused or exacerbated by emissions-delete modifications. The Magnuson-Moss Warranty Act protects consumers from blanket warranty denial, but GM's legal team aggressively argues that emissions tampering directly causes downstream failures (especially turbo and fuel system issues). If your truck is still under the 5-year/100,000-mile powertrain warranty, think very carefully before installing any delete equipment.
Q: Can I install this Catless downpipe myself?
A: If you're comfortable with mechanical work, yes — but plan for 4-6 hours and have a lift or ramps. Key challenges: Seized turbo bolts (years of heat cycles corrode the bolts; soak with penetrating oil overnight before attempting removal), Tight turbo area (the turbo-to-downpipe connection is the hardest working space on the truck), Sensor transfer (move the factory EGT sensor from the old pipe to the pre-drilled bung on the new downpipe — don't skip this), Photo documentation (take pictures before disassembly so you remember sensor and bracket placement). Tip: Don't forget to install your tune BEFORE or at the same time as the downpipe. Don't drive on stock programming with emissions equipment removed.
Q: Should I delete the EGR too with this downpipe?
A: Most L5P owners who install a Catless downpipe also delete the EGR for these reasons: The EGR cooler is a known failure point on the L5P — it can crack and contaminate coolant with exhaust gases. Deleting the EGR eliminates recirculating exhaust into the intake, improving combustion efficiency. The delete tune handles both DPF and EGR parameters simultaneously — doing one without the other can cause drivability issues. The Downpipe + EGR Delete Kit variant ($387) is the most cost-effective way to address both. Recommendation: If you're already investing in a tune (which you must), do the EGR delete at the same time. One tune covers everything; one installation session saves labor.
Q: How does this downpipe affect fuel economy?
A: The downpipe itself doesn't directly affect MPG — it's the tune that determines fuel economy. Most delete tunes are optimized for power and torque, which can lean toward richer fueling — not necessarily better economy. However, many owners report improved real-world highway MPG because the engine doesn't work as hard to maintain speed with reduced exhaust restriction. Heavy towing in-town may actually use more fuel if you're regularly accessing the extra power the tune provides. Realistic expectation: Highway MPG may improve 1-2 MPG; city/towing MPG stays roughly the same or slightly increases. Don't buy this product expecting dramatic fuel savings.
Q: What's the turbo elbow and why does it matter?
A: The turbo elbow is the first curved section right after the turbo outlet. On the L5P, the factory elbow is a restrictive cast-iron component with poor internal flow geometry, which creates turbulence and backpressure. Quality aftermarket downpipes (like the Flashark) feature smoother mandrel-bent transitions from the turbo flange into the main downpipe body. This matters because the turbo has to push exhaust against whatever resistance is downstream. A smoother elbow reduces turbo workload, improves spool time, and allows more efficient boost delivery. Combined with the 3.5" pipe diameter, it's the complete flow improvement from turbo to mid-pipe.
Q: Can I run this Catless downpipe on stock programming with no tune?
A: Technically it bolts on, but practically it's a bad idea. Without a tune, the ECM will immediately throw codes for missing DOC/DPF parameters. The truck will enter limp-home mode (significantly reduced power and a limited RPM range). DPF regeneration attempts will fail, potentially causing fuel system issues. You're spending money on a performance part that your truck's computer is actively fighting. Bottom line: If you're buying this downpipe, budget $500- $ 800 for a quality tune. The tune is what makes the entire system work. Without it, you're just creating problems.
Easy Return Policy
Every order comes with a 14-day free return, provided the item is brand new, uninstalled, and in its original packaging. We cover return shipping for quality issues. Refunds are processed within 3-5 business days. Click for Return Policy
