H2o-uk

iTrader: (1)

Hi guys,

As always I'm banking on your knowledge to help me through this difficult decision . My modification list on my MY03 Blob WRX is slowly growing see below :

Green Panel Air Filter
Prodrive Backbox
De resonated Rear pipe

Just bought a Silicon Intercooler Y-Pipe to be fitted

Now obviously im not expecting much from any of these mods, maybe 5bhp or so, so I was also looking at replacing the centre section with a decat pipe. What kind of figure would I be expecting from my car after ?

Does this then take it over the threshold where a remap is required, as I'd rather not have to do that just yet.

As always thanks for any advice.

Fat Boy

Nope

Decat all the way though and/or induction kit make major changes to air flow, before that with the sort of mods you're talking about no real need.

BTW the exhaust post turbo is 3 bits - downpipe, centre section and back box so not sure what you mean by de resonated rear pipe - I assume you mean centre section, if so all you have left to "decat" post turbo is the downpipe catalyst (which makes the single biggest difference).

mickywrx

iTrader: (29)

Cat in the up-pipe also IIRC on newage WRX's.

H2o-uk

iTrader: (1)

Yer, the Newage exhaust is in 4 sections I believe, Upipe with cat, Downpipe with cat, Centre section with cat, then theres a rear pipe and a backbox. There's normally a small resonator box on the rear pipe before the back box but mine hasn't got one just a straight through.

gus sti8

iTrader: (5)

does a 03 sti have a cat in theup pipe?

H2o-uk

iTrader: (1)

I believe so, and a sports cat in the downpipe. Im no expert, but I've asked a lot of questions on this subject over the last couple of weeks and I think thats one of the answers I had. If im wrong somoene will update with the correct answer im sure

Meallbhan

iTrader: (3)

Just to be oposite, I always heard that the STI had a straight through up pipe with no cat but the WRX had the cat. Not saying I'm right though.

Wulsey

iTrader: (1)

H2o-uk have a look at the link below it will keep you right.

http://www.andyforrestperformance.co.uk/58901.html

The sti has no cat in the up pipe as i replaced the up pipe in my old wrx bugeye with a sti up pipe along with sti tmic,sti pink injectors,vf34 turbo,air flow delete elbow before remaping and jumped from 283bhp after the first map to 340bhp/340lbft.

Fat Boy

That's why all my comments said 3 parts post (after) the turbo.

To be exact the exhaust system is 5 parts in total - manifold/headers, up pipe (with cat in newage), [turbo], downpipe, centre section, and back box ( which consists of a one piece combined backbox and a couple of feet of pipe)

H2o-uk

iTrader: (1)

Fat Boy I see what you are getting at, but on my exhaust system, after the visible cat underneath the car, there is a long peice of pipe about 3 ft long, then a flange and then then 2ft of pipe and backbox.

Meallbhan

iTrader: (3)

I think the only difference with the STI is thats theres no cat pre-turbo (up pipe).

H2o-uk

iTrader: (1)

Meallbhan, thats a good picture , ive seen it before but couldnt find it. The REAR PIPE as its called on there on my car has no resonator. All my cats are still in place currently.

53

iTrader: (41)

Green Panel Air Filter
Any other backbox
De resonated centre pipe
Second Decat 'short centre pipe'
Silicone Intercooler Y-Pipe

I would stop there for the time being.

You could silicone replace other bits and bobs but it's pretty unecessary atm.

H2o-uk

iTrader: (1)

Thanks for the response, that's great I kind of expected it. I suppose theres no point going further unless I'm prepared to replace the downpipe and then I'll need a remap for sure I would guess. Onto the brakes and suspension next my bank account hates me lol.

Thanks for all your help with this.

Norman Dog

iTrader: (1)

I replaced the downpipe on mine with a Sports cat and removed the up-pipe and centre pipe cat. I ran the car like this for about 4 months before remapping with no issues other than a couple of CEL's for cat below efficiency. You will instantly notice the difference in spool up/throttle response even before remapping too.

Fat Boy

Fair enough mate- and that drawing shows the same as you say, although the pic of the exhaust is how I understood it to be. Anyhoo no remap needed while the main cat is still in place

Cheers

FB