The act of cutting out exhaust restrictions like mufflers, resonators, and catalytic converters to install a continuous steel tube from the exhaust manifold to the tailpipe. Tuners do this to reduce exhaust backpressure and drastically increase engine volume. It makes the vehicle illegal for street use in most jurisdictions due to emissions and noise regulations.
If you straight-pipe that diesel, it's going to drone so loud on the highway you'll need earplugs.
Related terms
Straight-piped
Describing an exhaust system that has been stripped of its mufflers and emissions equipment.
Exhaust system
The piping and components that route spent combustion gases away from the engine.
Muffler
An acoustic chamber in the exhaust system designed to reduce the noise generated by combustion.
Catalytic converter
An exhaust emission control device that reduces toxic gases and pollutants into less harmful compounds.