Question about decating a WRX
 

Hi all
I,m am after a centre section unresonated to replaced the 3rd cat ( silencer ) on my 04 wrx , I thought I had got one off a fellow member but when it arrived , it was the pipe to replace the 2nd cat and not the centre section ,
My question is , once I have got a centre section and ready to fit it , can I fit this decat pipe and replace the 2nd cat at the same time so it will only have the one cat left , would it need a remap with the one cat left and would it pass a mot with the single cat on .
Don't really want to go down the remap route as its a bit expensive and i not really after power gain just a slightly louder exhaust note so that's why I was just changing the 3rd cat .
Thanks kev

Shouldn't have any issues, did the same to mine. I assume you've decatted the uppipe to? I ended up full decat but you will be fine.

I've not decatted anything yet , which is the up pipe ?
This is the pipe I was sent
http://i425.photobucket.com/albums/p...46ba248c83.jpg

And this is the pipe I am after
http://i425.photobucket.com/albums/p...f07e5499ad.jpg
So can I fit both without a remap and would it be MOT friendly , I not after a full decat so will not be doing the up pipe .

From what I understand the biggest gains are from buying a sports cat for the down pipe rather than sticking with the regular down pipe.

I don't know what you can and can't fit without a remap though.

Like I said I'm not really after power gains just a better exhaust note .

Ok, you can get rid off all the cats bar the one in the downpipe and still be mot friendly. If you remove the cat in the downpipe as well then yes you will need a remap and it won't pass it's mot.

The uppipe goes before the turbo and after the engine, I replaced mine first as the cat in the pipe broke its welds and started rattling, if left it would breakup and possibly destroy the turbo. If I was you, remove the centre section, uppipe and cat pipe. That will leave you with just the downpipe cat and still pass mot, plus more rumble depending on your back box.

Thanks for the info Kedlestone .

Right , I've just found a nice diagram and can finally get my head round it ,

http://i425.photobucket.com/albums/p...bdb1859abb.jpg

Right I have the decat mid pipe with the rear O2 sensor on it and will be getting a centre section without the resonator plus a scorpion backbox ,
So will only be removing the rear cat where the rear O2 sensor is and that leaves the pre- cat and the front cat which is in the down pipe so it will still have 2 cats left.
Would that be ok to do without a remap and it should still be mot friendly .

Bump

+1 here..

have a standard system and wondering how many cats there are, how many i can do away with and still pass MOT and at what point mapping becomes necessary in terms of the ECU supplying the right amount of fuel for the free-er flowing engine (i know even a catback will yield more with a map but thats not what im looking for here).

also does the ECU throw and faults/dash lights up after removing any or all of the cats?

Read my post again, your car will be fine as long as the downpipe hasn't been decatted as that's where the O2 sensor is.

DMcL, yes the ecu light will come on only when the downpipe has been decatted uauslly. All the other cats are fine to remove but yield greater gains with a remap.

I've done all this to my own in the past with no issues.

so i could throw on an aftermarket exhaust manifold (perhaps equal length), retain the cat after the turbo or substitute with a sports cat and then run whatever i want from there back with no CEL's? i know id need tuning for an equal length manifold, probably even for an aftermarket unequal length mani but for not qondering about the cats and what i need to leave in for the time being to avoid CEL's. looks like i should be fine with a catback for now, can deal with tuning if/when i think about going for a manifold/up pipe.

Manifolds are another question. But yes you could get rid of all cats after the downpipe and not have any CEL lights. Not 100% a sports cat wouldn't still throw a CEL up, usually you would map even them to get the best out of them. Best off asking a mapper.

yea i got the jist of mapping these. i come from a mapping background with old BMW's so the general rules apply. as the system in my WRX is newer, a different brand, etc, etc. for no im wanting to do what i can without mapping and without grenading the engine when i put my foot down as im looking into mapping options and heavily considering mapping myself once i have sussed the system out a bit more.

just how many cats are there on the newage WRX in total? (mines an 06 2.5 FWIW)? i was under the impression the DP was the last cat and assumed there may be one before the DP, possibly before the turbo.

if a CEL is thrown up does the car lose any power/go into limp mode or anything that would otherwise stop it from driving normally or is it just an annoying light in the dash until you get it sorted out/turned off.

Cats, 1 in uppipe before turbo, 2nd in downpipe, 3rd in cat pipe then mid section is just silencer and back box silencer.

Yes CEL will cause rough running and cut power, ie limp home mode.

Pretty sure it's catted on the up-pipe, downpipe and centre section, it was on the 2.0 WRX.

Apparently the rear o2 on the 32bit ECU's do have an effect on CL fuel trims, it can pull them down if decatted/removed. I'm not sure if OpenSource can switch this influence off, COBB can, not sure about ECUTek.

I've never heard or seen the P0420(removing CAT) CEL cause limp mode?

I want to decat (prehapes just 2 off. Them) but don't want to remap as I'm not ready for the power increase that comes with so I'll be watching this thread closely as well

Dose anyone know how meny. Cats will get you through the MOT?

By the info in this thread and some others that I have read , it seems you can remove the third cat in the mid pipe with no problems on the mot and I'm not sure but have read that you can change the downpipe to a sports cat like they do for a Ppp upgrade and still pass mot but not 100% on that but I'm sure someone will confirm this if its right or not .

Well iv recently found out since mines an import. It dosent need cats a all as there's no spec in the mot for it.
I'm more worried about the remap anyway

I think to be on the safe side if you fully decat it you need a remap .

Just a update , decat'd mid pipe and centre section and no problems with fault codes ' happy days .

Just made 256bhp and 262.4lbft on my 2.5 WRX with ebay 3" catback and an HKS panel filter :luxhello:

No remap?