Downpipe

On many turbo engines it contains the catalytic converter. It runs from the engine bay down to under the car. It is a frequent target for performance modifications. On cars with emissions testing, any replacement must keep a type-approved catalytic converter in place. Fitting is often harder than expected because of seized bolts near the hot turbo.

Exhaust gases flow from the turbine through the downpipe into the main exhaust.

Replacing it with one without a catalytic converter breaks emission rules. Its gaskets and joints can leak and cause a ticking noise.