kris130

Hi I have just aquired a standard 2004 wrx U.K.
I was thinking of putting a prodrive back box on it and replacing the 1st cat in the exhaust with a decat downpipe.
What knid of power gains should i get ??
Will I have any issues with warning lights and do I need to remap the ecu thanks in advance .

Leaney-g

You'll get around 10 extra horses.

And you won't have to do anything with the ecu just for that.

MrNoisy

iTrader: (28)

If you can see the search mate please use it for questions like this in future, as it's already been asked a billion trillion times before!!!

Ignore the above post too - if you're taking cats out of the equation, you shouldn't "just leave it".
If you're going to have a remap, the best thing you can do is either:
1) Replace the up pipe and centre section with decat versions (the STI up pipe will do), and a Prodrive or other back box, and then a sports cat if you are worried about MOT. OR
2) Go full decat, and replace the lot for more power.

I'd be tempted to go for a full system rather than buying bits - that way you can be sure it'll all slot together nicely. There are plenty of them floating about on here, ebay, Jap Performance Parts etc.

By the way - the up pipe is the first cat in the exhaust, and not the down pipe as you stated (on a WRX that's the second one).
See here

You will need a remap after doing this because you could potentially damage the engine if you run it like that for long without having it remapped.
Best thing to do - get yourself an aftermarket panel filter (such as Green, K&N etc) or an STI filter and bung that in at the same time.

If you go for the lot with the sports cat I reckon you'll see about 270bhp, maybe 280bhp.
With a decat, possibly more.

Mine made 248bhp with a Green panel filter, and the resonator and backbox replaced.

MrNoisy

iTrader: (28)

Double Post

NEILB1

iTrader: (9)

Righ i am confused at this, I HAVE A PRODRIVE rear box afterburner centre ok

Can i remove either the uppipe (pre cat) or the front cat converter with out getting it remapped ?

dynamix

iTrader: (3)

Possibly on a bugeye wrx but a remap will make sure it is safe and optimised (and get more power)

stevie turbo

iTrader: (12)

hi i just bought a bug on a x plate it has all cats removed so fails the mot,i dont know if its been remapped..
question is if i was to put a standard down pipe cat on it would it pass the emmisions test with the downpipe one in place ,

also my second lambda sensor is on the down pipe at the top behind turbo like a classic , arnt they normally on the third cat

dynamix

iTrader: (3)

it would probably pass the mot with the downpipe cat put back on.

They have probably fitted the second lambda there if there wasnt a boss for it lower down. It would throw up a cel code unless remapped or fitted with a resistor to fool it into not coming on.