A downpipe is a part of a cars exhaust system that allows the turbo aspect of the engine to be more effective by steering gases away from the turbine, creating more uninterrupted power. Aftermarket downpipes usually feature wider capacities and are less restrictive than the stock option, which allows for greater space for a faster turbo spin. There are two types of aftermarket downpipes: catted and catless. Catted downpipes come with a high-flow catalytic converter, which cleans exhaust gases as they pass through a catalyst, reducing air pollution. On the other hand, catless downpipes come without a catalytic converter, which means that the vehicle will emit a noticeable odor and the exhaust gases wont be cleaned before the vehicle emits them.

While catless downpipes can reduce back pressure to the turbo, making it spool up faster and resulting in higher power output and less turbo-lag, they can also trigger a CEL (check engine light) due to O2 sensor detecting more NO2 and CO than the threshold, which can be removed by most piggyback ECU flash. Catless downpipes are also bad for the environment and can be illegal to drive on normal roads. Catted downpipes, on the other hand, are preferred over the catless configuration on public roads and if you use your vehicle frequently, as they are more environmentally friendly and can provide more space for airflow than stock downpipes from the factory, increasing the overall efficiency.