Downpipe: decat or high-flow catalytic converter for your Stage 2?

Decat or high-flow catalytic converter: the difference

A downpipe is the first section of the exhaust, right after the turbine. It comes in two main versions:

• Decat: the catalytic converter is removed. The exhaust flows as freely as possible and the sound is rawer.
• High-flow catalytic converter: the stock catalytic converter is replaced with a less restrictive one that lets exhaust gases flow more freely while still providing emissions control.

Stage 2 and ECU tuning

A downpipe without ECU tuning offers little benefit: it is the ECU map that makes use of the increased flow. A Stage 2 setup generally combines the downpipe, a matching exhaust and a dedicated ECU map. In both cases, the tune must account for the downpipe version chosen, so be sure to specify it when ordering.

O2 sensors

A modern vehicle monitors its catalytic converter with one sensor upstream and one sensor downstream. Without a catalytic converter, the ECU detects that emissions control is no longer taking place and may turn on a warning light or limit engine power. With a high-flow catalytic converter, the ECU receives a signal closer to stock, but an adaptation may still be required depending on the model. In any case, don't just install the part: plan for the matching ECU map.

Vehicle inspection and road use

• Decat: removing the catalytic converter is not compliant on a vehicle used on public roads. It is intended for motorsport use only.
• High-flow catalytic converter: it may be suitable for road use only if the part number is homologated. This is stated in the product description, part number by part number.

Which one to choose?

• Road car: choose a homologated part number with a high-flow catalytic converter.
• Race car: the decat delivers the maximum gain.

Browse downpipes

Browse the Hubshop downpipes category to find part numbers by model. Before ordering, check your engine using your VIN.

Legal notice: removing or modifying the catalytic converter, particulate filter or sensors of a road vehicle is prohibited. Non-homologated downpipes are intended for motorsport use only, on a closed circuit or off public roads.