What a downpipe is, how much performance it gains and whether it is legal

On a turbo engine, the downpipe is the first section of the exhaust: the pipe that leaves the turbine and runs down to the rest of the system. On most factory cars it houses the main catalytic converter and is one of the narrowest points of the whole exhaust.

Why it gains power

A turbo works on the pressure difference before and after the turbine. The more freely the gas flows out, the sooner the turbo spools and the less the engine has to push. That is why a larger downpipe with a less restrictive catalyst is the exhaust part that frees up the most performance on turbo engines, especially together with a remap that takes advantage of that flow. The exact gain depends on the engine and the software: when the manufacturer publishes dyno figures, you will see them on the product page.

With or without a catalyst

• With a sports catalyst: keeps exhaust treatment with a higher-flow cell. The option for a road car.
• Without a catalyst: intended for track use. Removing the catalytic converter is not legal for road use in Spain and in most of Europe.

What else to bear in mind

A downpipe can trigger the engine warning light if the ECU reads different values at the rear sensor, so it is usually fitted together with a remap. And since it modifies the exhaust system, check its road approval for your car before buying.