GM Duramax L5P 3.5" Down-pipe 2017-2023

This 3.5" turbocharger downpipe (also known as the turbo direct pipe) will remove the DOC and increase exhaust flow out of the turbo, improving performance.  There are other versions of this pipe that start behind the Diesel Oxidation Catalysts, leaving it installed for emissions-on setups but this pipe will fully remove the DOC for the best airflow and power gains.
 
Both DPF delete pipes, and full exhaust systems do not include a DOC delete, this pipe is needed to fully remove your emissions but isn't required for a delete tune.