Q: Can I take the cat off my car (de-cat) to improve performance? A: Removing the cat (Catalytic converter) from any exhaust system will often improve a cars performance due to the increase in exhaust gas flow it allows. You should however consider it seriously before going down this route. There are a few myths that surround the legality of cat removal in the UK and a few things worth noting if you do remove it. Myths: a) Removing the cat is illegal. This is simply not true, you are perfectly entitled to remove the CAT from your car and fit a de-cat (straight through) pipe as long it will still pass the relevant MOT emissions test. b) If you remove the cat it WILL fail the MOT emissions tests. Again this may not be the case. The Japanese car industry had far stricter emissions requirements than the UK and cat's were fitted to home market Japanese cars for a long time prior to them becoming a requirement in the UK. In most cases you can quite easily remove the cat from any Japanese grey import car that was first registered on, or before, 31st July 1995 (M-reg or earlier) and still pass the less stringent UK MOT emissions test. Removing a cat from a more modern car will almost definitely mean failure of the later more stringent emissions limits. It is worth noting that some tuned Evo's with an aftermarket ECU can pass the later emissions test even with the cat removed. Please note that in the UK, new roadside emissions testing is being introduced for passenger cars. If your car fails the test and it is found that you have removed the cat then it will be very probable that you will be fined. The fines depend on the part of the country you are in, some councils being stricter than others with even 4 and 5 figure sums being mentioned, with cars being impounded until the fine is paid. You have been warned! As with any modification, always tell your insurer. Back to question page