Introduction
Whether you’re chasing that extra kick of performance or desire a more resonant growl from your exhaust, an aftermarket downpipe might be on your modifications list.
But a crucial factor to consider before you make that change is whether the downpipe will pass emission tests. After all, a failure on this will mean your car isn’t road legal.
Let’s dive into the details to provide an informed answer.
Catted vs. Catless

Let’s get to know downpipes a little better.
An aftermarket downpipe can be categorised into two types: catted and catless.
Catted Downpipes: Catted downpipes include a catalytic converter (often a high flow sports cat). This device acts as a converter, changing harmful exhaust emissions into less harmful substances. These provide performance gains while remaining road legal.
Catless Downpipes: As the name suggests, catless downpipes do not feature these converters, resulting in a free, unrestricted flow of exhaust gases that enhances performance. However, they don’t cut down on emissions and will always fail an emissions test.
Passing The Emissions Test

If your primary concern is passing your emissions test, a catted downpipe is your best bet.
Catted downpipes, as long as they are of high quality, are designed to reduce emissions effectively and should allow your car to comply with emissions regulations in the vast majority of places.
On the other hand, a catless downpipe will not pass an emissions test. Devoid of any mechanism to reduce harmful emissions output, these downpipes result in an instant fail and are manufactured for track use only.
Get Your Exhaust Hot!

To maximise the chances of passing an emissions test, especially if you have a high flow sports cat in your downpipe, it’s essential to ensure your exhaust system is hot before testing.
A warm catalytic converter is more effective at reducing harmful substances in exhaust gases.
Give the car a good solid drive for 15 minutes or so before the test. Don’t be afraid to rev it out (as long as the engine is up to temperature).
Doing this will ensure borderline catted downpipes that feature 200 cell high flow sports cats should still pass emission testing.
Happy modding!