3.5'' Downpipe Exhaust For 2017-2023 Chevy/GMC Silverado/ Sierra L5P Duramax Diesel 6.6L

Fitment:

• 2017-2023 Chevrolet Silverado 2500 & 3500HD - L5P Duramax Diesel 6.6L Pickup Trucks
• 2017-2023 GMC Sierra 2500 & 3500HD - L5P Duramax Diesel 6.6L Pickup Trucks

Note: Will not fit Cab & Chassis trucks.

Q1: What trucks does the L5P downpipe fit?

A1: This downpipe is designed for the 2017-2023 GM Duramax L5P 6.6L diesel engines found in the Chevrolet Silverado 2500/3500 HD and GMC Sierra 2500/3500 HD. The L5P was introduced in 2017 and carries through the 2023 model year before the L5P was discontinued. If you have a 2016 or earlier Duramax, or a 2024+ model with the L5P or new diesel, this isn't your part. The 2017 refresh introduced a new turbo housing that requires the L5P-specific downpipe.

Q2: Do I need a tune after installing the L5P downpipe?

A2: Yes, almost definitely. The factory ECU sees the DPF and DOC as part of the exhaust system backpressure parameters. Remove them and you need to either tune around it or you'll get check engine lights and reduced performance. A quality tune from vendors like PPE, EZ-Lynk, or DuramaxTuner will recalibrate the fueling and tell the ECM to ignore the missing emissions equipment. Without a tune, you're basically telling your truck something's wrong and it will try to protect itself.

Q3: How much power does the duramax downpipe add?

A3: On a completely stock truck, you might not even feel it until you add a tune. The real gains come when you stack the downpipe with intake, exhaust, and proper tuning. Expect 50-100 extra horsepower and 100-150 lb-ft of torque with a full delete package and aggressive tune. The L5P already makes decent power from the factory, so the downpipe really unlocks what the turbo could already be making if it wasn't choked by the restrictive stock exhaust.

Q4: Is the L5P downpipe street legal?

A4: No. Removing the DPF, DOC, and other emissions equipment violates federal emissions laws in the United States. The Clean Air Act prohibits tampering with emissions control devices. California, New York, and states that follow CARB standards are especially strict. You risk fines, failed inspections, and potential legal issues. This downpipe is designed for off-road use, race trucks, and vehicles registered in states without emissions testing. If you're daily driving and need to pass inspections, this isn't the route to go.

Q5: What's the difference between 3.5 inch and 4 inch downpipe for L5P?

A5: The 3.5 inch is the most common upgrade that balances flow with keeping the exhaust velocity high enough for proper turbo spool. The 4 inch option provides maximum flow for heavily modified trucks pushing serious power. For most builds, 3.5 inch is plenty. Going 4 inch only makes sense if you're running bigger injectors, a bigger turbo, and making over 700 horsepower. The larger pipe can actually hurt spool on lighter builds because exhaust gas velocity drops too much.

Q6: What does DPF delete mean and why do people do it?

A6: DPF stands for Diesel Particulate Filter. It's a honeycomb ceramic filter that captures soot from the exhaust. Over time it fills up and the truck burns it off through regeneration cycles. Problems arise when the DPF gets clogged, the regeneration fails, or you need to replace a $2000+ filter. A DPF delete removes this component entirely, along with the related sensors and ECM parameters. The trade-off is better fuel economy, more power, and no DPF-related headaches, but you lose emissions compliance and typically void the powertrain warranty.

Q7: Will this downpipe void my duramax warranty?

A7: GM can deny warranty claims if they determine your modification caused the failure. They'll look for any excuse, especially if you have a check engine light related to the emissions delete. However, many owners run deleted trucks for years without issues. The EPA and FTC have rules about warranty discrimination for parts that don't directly cause failures, but GM's legal team is aggressive. If your truck is still under factory warranty, think carefully about the consequences.

Q8: Can I install the L5P downpipe myself?

A8: If you're comfortable with mechanical work, it's doable but plan for 4-6 hours. The biggest challenge is removing the old downpipe bolts, which are often seized or rounded from heat cycles. You'll need a lift or ramps, basic hand tools, and penetrating oil. The turbo to downpipe connection is the tightest area to work in. Take pictures before disassembly so you remember sensor placements. Don't forget to transfer the downpipe temperature sensor to the new pipe.

Q9: Do I need to delete the EGR too with the downpipe?

A9: Not necessarily, but most guys who delete the DPF also delete the EGR (Exhaust Gas Recirculation) for a few reasons. The EGR cooler is known for failures on the L5P and can cause coolant contamination. Removing it eliminates that problem and adds more power since you're not recirculating exhaust gas. It's usually sold as a kit with the downpipe. The tuning takes care of both deletions. Doing just one without the other can cause driveability issues.

Q10: How does the L5P downpipe affect fuel economy?

A10: The delete itself doesn't guarantee better MPG. What changes fuel economy is the tuning that comes with it. Most delete tunes are optimized for power and torque, which can lean toward the opposite of fuel economy. However, many owners report better real-world MPG because the truck doesn't work as hard to maintain speed with less exhaust restriction. You'll see the biggest gains on the highway. In town with heavy towing, you might actually use more fuel if you're getting into the power you're paying for.

Q11: What's the turbo elbow and why does it matter?

A11: The turbo elbow is the first bend after the turbo outlet. On the L5P, the stock elbow is a restrictive cast-iron piece that creates turbulence and backpressure. An aftermarket turbo elbow (often included with quality downpipes) has smoother bends and better transitions to the downpipe. This matters because the turbo has to push against whatever resistance is downstream. A better elbow reduces turbo stress, improves spool, and allows the turbo to breathe more efficiently.

Q12: Can I run this with stock programming if I don't tune?

A12: Technically yes, but you'll probably get constant check engine lights. The ECM monitors the DPF pressure differential sensor and will throw codes when it sees abnormal readings. Some people run unplugged sensors with stock tuning, but this causes limp-home mode and reduced power. If you're spending money on a downpipe, budget for a tune too. The tune is what makes the whole system work properly. Without it, you're just ticking time bombs on sensors and potentially hurting your turbo.