The Rog Journal

Is a cat-back exhaust legal in the UK? What the MOT checks.

6 min read

This article is written for: United Kingdom. For your country: Is a cat-back exhaust legal in California? And in your state?

Updated 30 October 2026.

A cat-back exhaust leaves your factory catalytic converter, oxygen sensors and on-board diagnostics exactly as they are, and with a Rog valved system, valves closed, your car sounds very close to stock, day to day and at the MOT. Valves open, it has the voice you chose for it. If you replace the front section too, our 200-cell sports catalytic converter keeps emissions control. Each system is built from your VIN, from a 3D scan of the chassis and of the original system, and bolts onto the original mounting points with no welding. Free technical documentation for your paperwork, a 3-year warranty and free delivery, with duties and taxes included in the price.

What you get with Rog.

  • The sound you choose: you configure your system (design, material, catalytic converter, valve control), and you open the valves whenever you like, on a clear road or on track.
  • A discreet car when it matters: valves closed, the sound stays very close to stock, in your street and at the MOT.
  • A system made for your car: built from your VIN, from a 3D scan of the chassis and of the original system, checked before production; it bolts onto the original mounting points with no welding, at the garage of your choice.
  • Emissions control kept: a cat-back keeps your factory catalytic converter; as an option, a 200-cell sports catalytic converter keeps emissions control; the catless version is for track use only.
  • Valves controlled by your car's original drive modes or by the Rog remote.
  • The technical documentation for your system, free, on request, for the MOT or for your insurer.
  • 20 working days to build and deliver, free delivery, 3-year warranty, duties and taxes included in the price.

Find the exhaust for your car

Your vehicle.

Choose your model: we show you its exhaust, its options and the lead time.

We check compatibility with your VIN before manufacturing.

Contents 6
  1. At the MOT: how it works.
  2. The rules, in short.
  3. Find the exhaust for your car.
  4. Frequently asked questions.
  5. Write to us.
  6. Sources.

At the MOT: how it works.

  • Noise is judged by ear: during the emissions test, the tester revs the engine to around 2,500 rpm and uses their judgment, comparing your car with a similar vehicle fitted with a standard muffler in average condition. The manual sets no decibel figure. Valves closed, your car goes in sounding very close to stock.
  • Emissions equipment: on a gasoline car first used on or after 1 September 2002, the tester checks that the factory emissions control equipment (catalytic converters, oxygen sensors) is present and not obviously modified or defective (section 8.2.1). A cat-back leaves it untouched.
  • Security: every part of the noise suppression system must be secure. A Rog system bolts onto the original mounting points.
  • How often: first MOT by the third anniversary of registration, then every year.
  • Your V5C: an exhaust is not on the DVLA's list of changes to record in your log book. Your VIN is printed on it: it is all we need to build your system.

The rules, in short.

Rog exhausts carry no type approval: that is a choice, because a system with type approval sounds almost like the original one, and the valves give you both. Regulation 54 of the Road Vehicles (Construction and Use) Regulations 1986 asks for an exhaust and muffler kept in good working order and not altered so as to increase the noise made by the exhaust gases; UN Regulation No. 59, the international standard for replacement mufflers, asks a system with several modes to meet its requirements in each of them. For a sports catalytic converter, as for the noise, it is the MOT tester who decides.

On the road, regulation 97 asks drivers not to make excessive noise that could reasonably be avoided: valves closed in town, your car stays close to stock, and the police officer decides. In Kensington and Chelsea, noise cameras back up a Public Spaces Protection Order that targets driving behavior: engine revving, rapid acceleration and racing. Details in our table of noise cameras in Europe.

Find the exhaust for your car.

Each product page shows the system, its options and its sound; each guide explains the configuration in detail. A few examples:

Your car is not on the list? All our exhausts, by brand.

Frequently asked questions.

Valves closed, is my car discreet?
Yes: valves closed, the sound stays very close to stock, day to day and at the MOT, and you open the valves when you choose. At the MOT, the tester decides.

Does the MOT measure exhaust noise with a meter?
No figure is set: the tester uses their judgment during the emissions test, at around 2,500 rpm, against a similar car with a standard muffler in average condition. The MOT tester decides.

Will the system fit my car?
Yes: it is built from your VIN, from a 3D scan of the chassis and of the original system, and checked before production. It bolts onto the original mounting points with no welding, at the garage of your choice.

What happens to my catalytic converter?
With a cat-back, it stays in place. If you also replace the front section, the 200-cell sports catalytic converter keeps emissions control; the catless version is for track use only. At the MOT, the tester decides.

Does a cat-back change my ULEZ or Clean Air Zone status?
No: TfL enforces the ULEZ on your car's declared emissions standard (Euro 4 for gasoline cars), Clean Air Zones use the same Euro standards, and a cat-back leaves the catalytic converter and the declared standard as they are.

Does Rog provide documents?
Yes: on request, we send you the technical documentation for your system free of charge, describing your configuration, for the MOT or for your insurer, whom you should tell before fitting. At the MOT, the tester decides.

Write to us.

Email us at contact@rogmotorsport.com: we reply in writing, in English, within 24 hours. For instant answers: the Rog Advisor and our FAQ.

As set out in our terms and conditions of sale, it is up to each buyer to check the rules in their country.

Sources.

  1. DVSA, MOT inspection manual for private passenger and light commercial vehicles, section 8 (8.1 noise, 8.2.1 emission control equipment), accessed 29 October 2026: https://www.gov.uk/guidance/mot-inspection-manual-for-private-passenger-and-light-commercial-vehicles/8-nuisance
  2. GOV.UK, "Getting an MOT", accessed 29 October 2026: https://www.gov.uk/getting-an-mot
  3. GOV.UK, "Change vehicle details on a V5C registration certificate", accessed 29 October 2026: https://www.gov.uk/change-vehicle-details-registration-certificate
  4. The Road Vehicles (Construction and Use) Regulations 1986, regulation 54, accessed 29 October 2026: https://www.legislation.gov.uk/uksi/1986/1078/regulation/54
  5. The Road Vehicles (Construction and Use) Regulations 1986, regulation 97, accessed 29 October 2026: https://www.legislation.gov.uk/uksi/1986/1078/regulation/97
  6. UN Regulation No. 59, replacement silencing systems (Official Journal of the EU, L 2025/844), points 6.1.3.2 and 6.2.3, accessed 14 October 2026: https://data.europa.eu/eli/reg/2025/844/oj
  7. Royal Borough of Kensington and Chelsea, "Hundreds fined as noisy drivers hit rock concert volumes", 15 October 2026, accessed 29 October 2026: https://www.rbkc.gov.uk/newsroom/hundreds-fined-noisy-drivers-hit-rock-concert-volumes
  8. Transport for London, ULEZ standards for cars, accessed 29 October 2026: https://tfl.gov.uk/modes/driving/ultra-low-emission-zone/cars
  9. GOV.UK, "Driving in a clean air zone", accessed 29 October 2026: https://www.gov.uk/guidance/driving-in-a-clean-air-zone

The Rog team

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