Duramax diesel hood badge on Chevrolet HD truck

Duramax 6.6 Downpipe and Delete Pipe Fitment FAQ

Duramax fitment questions almost always come back to one thing: the flange on your downpipe. GM changed it more than once on the 6.6L, and the right Polar Diesel delete pipe or exhaust depends on which one your truck has. This FAQ covers 2011-2026 Chevrolet and GMC 6.6L Duramax trucks, from the LML to the current L5P, so you can order the right parts the first time.

Duramax 6.6 delete pipe exhaust

Off-road and competition use only. Polar Diesel delete pipes, downpipes and full exhaust systems are built for off-road and race use. They are not intended for use on public roads or highways, and they require aftermarket tuning. Check the rules where you live before you buy or install.

Which Duramax do I have?

Start here, because the engine code decides everything else:

  • 2011-2015 LML: V-band style downpipe from the factory.
  • 2015.5-2016 LML: Mid-year change to a 3-bolt flange style downpipe.
  • 2017-2026 L5P: OEM style 4-bolt flange off the downpipe.

If you're not sure whether your 2015 or 2016 truck is an early or late build, look at the connection where the downpipe meets the rest of the exhaust. A round clamp means V-band. A flange with three bolts means 3-bolt.

What does the downpipe do?

The downpipe is the first section of exhaust after the turbo. It carries exhaust from the turbo down to the rest of the system, so its flange style decides which delete pipe or exhaust will bolt up behind it.

I have a 2011-2015 LML. What fits?

These trucks already have the V-band style connection, so Polar Diesel 2011-2015 systems bolt up to the factory downpipe:

Muffler versions of the full exhausts are also offered. You can compare everything in the 2011-2016 Duramax exhaust collection.

I have a 2015.5-2016 LML with the 3-bolt downpipe. What are my options?

You have two ways to go:

  1. Keep the factory 3-bolt downpipe and buy a system built for it, like the 2015.5-2016 Duramax 6.6L Polar Delete Pipe, the 2015.5-2016 5" Polar Exhaust or the 5" version with muffler. These are made for 3-bolt trucks only.
  2. Convert to V-band with the 2011-2016 Duramax 6.6L Polar Downpipe (part number PD-1-32328000). It's T304 stainless with billet machined flanges and heat wrap, and it converts 3-bolt 2015.5-2016 trucks to the V-band style. After that, you run the 2011-2015 V-band systems listed above. This downpipe only works with V-band style exhausts.

All of the 2015.5-2016 options are in the 2015.5-2016 Duramax exhaust collection.

Will the LML delete pipe fit my cab and box?

For 2011-2016 delete pipes and full exhausts:

  • Cab and chassis: Will not fit.
  • Regular cab: Fits, but must be modified.
  • Delete pipes: The factory tail section of the exhaust must be cut to length.
  • Full exhausts: Depending on your box and cab, one cut may be needed to set the overall length, and on systems with a muffler.

I have a 2017-2026 L5P. What fits?

L5P trucks use the OEM style 4-bolt flange off the downpipe, and every Polar Diesel L5P system is built around it. Your choices:

Browse them side by side in the 2017-2019 Duramax exhaust collection or the 2020-2023 Duramax exhaust collection.

Will the L5P delete pipe fit my cab and box?

For 2017-2026 L5P delete pipes and full exhausts:

  • OEM style 4-bolt flange off the downpipe: Required. These systems only fit trucks with it.
  • Crew cab, short box, long box and dually: Listed as fitting on the full exhausts.
  • Regular cab: Must be modified.
  • Delete pipe: The factory tail section of the exhaust must be cut to length.
  • Full exhausts: Depending on your box and cab, one cut may be needed to set the overall length, and on systems with a muffler.

Do I need a new downpipe on my L5P?

The L5P delete pipe and exhausts connect at the factory 4-bolt flange, so the product pages don't list the Polar downpipe as required. It's an upgrade over the factory piece if you want a stainless, heat wrapped downpipe that matches the rest of your Polar Diesel system. You'll find it in the 2020-2023 Duramax downpipe collection.

Do I need tuning?

Yes. Delete pipes, downpipes and full exhaust systems on the 6.6L Duramax require aftermarket tuning and modifications to run properly. If you'd rather not piece it together, a Polar Diesel Power Package bundles hard parts with tuning for your year range, such as the 2011-2016, 2017-2019, 2020-2023 and 2024-2026 Duramax 6.6L Power Packages. Many owners also pair exhaust work with an EGR delete, which we cover in Duramax 6.6 EGR cooler problems and why owners delete.

I want to keep my DPF. What should I buy instead?

Go with the 2011-2026 Duramax 6.6L 5" Polar DPF Back Exhaust. It replaces only the section behind the factory aftertreatment, so the DPF stays on the truck, and it fits every 2011-2026 6.6L except cab and chassis models. Our DPF-back exhaust buyer guide explains the options, and the Duramax 6.6 DPF-back install guide walks through the job.

How hard is the install?

Polar Diesel delete pipes, downpipes and exhausts are designed with an easy, hassle-free install in mind, with pre-bent hangers, stainless lap joint clamps and precise flanges. Use the install guide for your year: 2011-2016 Duramax 6.6 exhaust or 2017-2026 Duramax 6.6 exhaust. You can also download the official PDFs from the Polar Diesel installation guides hub. Let the exhaust cool completely before you start.

Quick fitment checklist before you order

  1. Confirm your engine: 2011-2015 LML, 2015.5-2016 LML or 2017-2026 L5P.
  2. On a 2015 or 2016, check your downpipe connection: V-band or 3-bolt.
  3. On a 3-bolt truck, either buy the 2015.5-2016 system or add the V-band conversion downpipe and run a 2011-2015 system.
  4. Confirm your cab and box. Cab and chassis is not supported on LML systems, and regular cab trucks need modification on every year.
  5. Plan your tuning before the parts arrive.

Related reading

Still not sure what fits your truck? Reach out to the Polar Diesel team with your year, cab and box, and we'll point you to the right part.

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