buying guide
How To Choose Downpipe Diameter For A Diesel Truck
Why 3, 4 and 5 inch downpipes exist and how to match the size to the truck and the rest of the exhaust.
Start With What Is Already On The Truck
The downpipe is the first section after the turbo, so it sets the ceiling for everything downstream. Fitting a 5 inch downpipe ahead of a 3 inch system moves the restriction rather than removing it. Match the downpipe to the exhaust the truck already has, or plan both together.
What The Sizes Are For
Broadly, 3 and 3.5 inch pipes suit trucks kept close to standard where drivability and noise matter. 4 and 5 inch pipes belong on trucks that tow hard or that have been built for higher output, where exhaust gas temperature is the limiting factor. This catalogue lists downpipes at 3, 3.5, 4 and 5 inch depending on the platform.
Fitment Traps
Model years matter more than model names on diesel pickups. Cab and Chassis trucks differ from pickups in the same range, and a part that fits one may not fit the other. Read the exclusions on the product page before you order, and if the truck is a variant, ask before you commit.
Emissions And Local Rules
Downpipe changes touch emissions equipment on many trucks. Rules differ by country and by state, and no part in this catalogue carries an emissions approval claim. Confirm what is legal in the market you sell into before you list a part.
Related categories
Parts covered
Products This Guide Applies To
Answers
Questions On This Topic
Is bigger always better?
No. An oversized pipe ahead of a smaller system gains nothing, and on a lightly modified truck it mostly adds noise.
Which sizes do you stock?
Downpipes are listed at 3, 3.5, 4 and 5 inch across Duramax, Cummins and turbo platforms depending on part number.
Do I need a new gasket?
Plan on a fresh turbo outlet gasket. Reusing a heat cycled gasket is the most common cause of a leak after installation.
Ask Before You Order
A two line email about the vehicle and the job saves a return later.