ok folks a quick question iv got a 1999 civic coupe em1 with a cat back system on it and ive just bought a de cat pipe what gains will that give me and will it make the exhaust louder?
thanks for any input
A de-cat is not worth the hastle of having to swap it out come MOT time either. You're just destroying the planet for 1hp. Maybe. A high flow cat will still give you a gain (it's clean for starters) and keep things clean and you'll pass your MOT without messing about with a de-cat also.
If you have a proper intake, a good header and a good exhaust you might see up to 8whp if you're lucky, you'll need to spend some cash to get 'real' gains however.