De-Cat Vs Sport Vs Bashing The Internals Out?

[James Trendall]

As the titles suggests. I'd like to either run a sports cat or decat the entire exhaust on my IS200 (52 plate) To be honest i really don't want to be messing around each year swapping the decat and original exhaust over.

What would be the better option?

£150+ on getting a sports cat manifold?

£0+ Elbow grease bashing out the cat's internals?

Would the O2 sensor start throwing problems at me if i remove the internals of the cat? Would it develop a nasty raspy sound from the engine due to the flow bouncing around the now hollow cat?

My exhaust is already nice and shiny from lots of grinding and polishing so no need for looks etc...

Anyone ran their IS200 decat or bashed out the internals etc..?

Also how likely will it fail on emissions without a cat? Would i be looking at a good service before hand or adding a more restrictive muffler at the end for the mot?

Thanks in advance.

[Cracksta]

My understanding is, if you remove the cat then your emissions would be too high so would fail on MOT, this is the same as bashing the cat internals in too? Meaning you'll need to put in your OEM one to pass.

Sport cats are designed to be more free flowing but lets you pass MOT too.

Best speak to an exhaust expert, I'm guessing it sound you want since performance mods doesnt make much difference on these cars.

[Stuno1]

If you completely decat the exhaust you will fail a mot and will most certainly throw a cel. A sports cat has a lower cell count so flows more freely than a stock car and will pass an mot. If you just remove the second cat and maintain the primary cars you may pass an mot but I can't be sure but a specialist may be able to advise you.

A decat pipe will be the same diameter as your current pipes so will not cause and gas flow issues with back pressure. If you gut your cat then the bore will be a different size to the rest of your system and will reduce back pressure and torque.

Either get a sports cat or a decat pipe and check it can pass an mot.

Stu

[andyk134]

Is there anyone here who has actually done exhaust mods who would like to comment fully? As I understand it the exhaust is a pipe within a pipe so there is a bit of restriction there. A few months back I changed the back box for a powerflow one and the pipes for the rear section were just one pipe with no internal restriction. There was a noticeable difference in performance, I know many here say it makes no difference. I had had my car 6 years and know it well, but changing the back box did make a difference, so their are improvements to be had if you do it right. Is there some one out there who has changed everything from manifold backwards who can give their input on performance?

With the cats out it will fail the MOT, that's the point of them, so you either need a sports cat that will pass, a decat and change it once a year (not really a big job) or a friendly garage to get it through......

[James Trendall]

Cheer's for the replies.

I'm after sound and a less restrictive exhaust as i'm slowly sourcing the parts to supercharge my IS.

I started to flirt with the idea of getting a second manifold and sliding a bit of pipe through the cat to create a decat pipe. I guess i could chuck it in for a free emissions test just to see how bad it would fail the mot. This was the back pressure should still remain as the pipe would go from a 2" to 1.5" back to 2" after the cat.

I'll give this a try first and report back with the emissions test showing if it passed/failed and how good/bad it was. Just the manifold from a breakers is pretty cheap anyway. Thanks again for the replies guy's fingers crossed on the emissions.

[Felix200]

Hi James,

You made any progress/got an outcome on this yet?