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Are Aftermarket Downpipes Legal In The UK?

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Amidst the thrill and passion for modding your car with an aftermarket downpipe, one question that frequently arises among enthusiasts is about the legality associated with these changes.

Before we delve into the heart of it, let’s establish a quick understanding of aftermarket downpipes and the two main types as this directly affects their legality in the UK.

Breaking Down the Aftermarket Downpipe

A downpipe forms part of your car’s exhaust system and connects directly to the turbocharger. Its main role is to guide exhaust gases away from the turbocharger down to the rest of the exhaust system, thereby reducing backpressure and increasing engine efficiency.

Aftermarket (and often larger) downpipes are frequently installed as a performance mod to improve power and gain some extra sound from the the tailpipes.

There are two main types of downpipes: catted and catless.

Catted Downpipes: These downpipes include a catalytic converter, designed to reduce harmful exhaust emissions by converting pollutants into less harmful substances. A catalytic converter is a legal requirement in the vast majority of places for cars used on the road.

Catless Downpipes: As you might guess, these are downpipes without a catalytic converter, allowing for an even freer flow of exhaust gases, and hence, a slight edge in performance. However, they result in higher emission levels, making them illegal for road use.

The Legalities In The UK

Under the UK law, it is mandatory for all cars to have a catalytic converter fitted. Therefore, using a catless downpipe would be illegal, as it directly contravenes emission regulations outlined under the UK’s MOT test. 

On the other hand, catted downpipes are generally considered legal as long as they meet the emission standards.

If you replace your original downpipe with a high-flow, catted aftermarket downpipe, and your vehicle still passes the MOT emission tests, you are within your legal rights to use it.

Most aftermarket downpipes that are sold for road use will make use of high flow sports cat’s. These improve performance while still remaining compliant for emission testing. Always aim to buy from a reputable and quality brand to ensure the high flow cat fitted in these downpipes will pass emission tests. 

Most catted downpipes are sold with 200 cell cats which are normally okay. To ensure they pass the emissions tests, you may need to get the car up to temperature first and get the exhaust hot. Give it a good, hard drive for 10-15 minutes before the test and you should be golden.

Wider Implications

Apart from the immediate legal implications, it’s vital to consider other repercussions. For instance, any modification to your car needs to be declared to your insurer, including the addition of an aftermarket downpipe. Failing to report such modifications could result in your insurance policy being declared void in case of a claim.

In the UK, there are many fantastic car insurers that specialise in policies catered to modified cars such as Adrian Flux. With these types of insurers, modifications such as a downpipe may have little to no effect on your insurance premiums!

Happy modding!