03 JDM STI exhaust question
 

Hi all. I have a jdm sti my03 with an afterburner centre section and back box. If im going decat then do I need just one down pipe or does it come in two sections or is it just one like on a classic. I've seen diagrams which show two cats: one in the down pipe and one in the mid pipe. Is this still the same in my jdm?

Thanks.

You only have a cat in the down pipe.

There's two mate. there's the downpipe and then the cat pipe. They both have cat's in them. I used to have a fully decated afterburner system.

It's a nice loud system

http://www.scoobyworld.co.uk/catalog...roducts_id=447

http://www.scoobyworld.co.uk/catalog...roducts_id=179

I've got the cat pipe decated left for sale mate. PM me if interested, I'll do it half price.

There's two mate, I've still got my old subaru ones in the garage and they've defo got cats in them. I also changed my pipes in stages and both times gain a fair bit of power etc

Have a look at the scoobyworld links. Afterburner is their own brand

I think the JDM's just have a cat in the downpipe and UK models have 2 but don't quote me on it

Sorry guys, my bad. I'd didn't read the JDM part :brickwall

I can only say for UK versions

You have the longer centre section as found on classics, ensure the downpipe will fit ;)

Tony:)

Thanks guys. next question- when I go fully decat I'm pretty sure that It will be too loud (motorways etc) if that is the case then can I swap out the back box for something quieter, say a prodrive one, without losing power?

When I had a fully decated afterburner system it was really loud. I never really went over 70 cruising just due to noise. I was at 105db at 5k revs. I had an sti backbox spare that I was gonna swap over for track days.

It's a very loud system. I loved it, sounded great but was a bit too much if I was gonna do a lot of motorway miles. I only changed to a milltek because of track noise restrictions

Ok, time to go quieter. Can I just swap the back box then?

Tony, slightly confused. Is the after burner centre section longer meaning that I need a classic fitment down pipe?

Thanks guys

IMHO I would if you're gonna do motorway miles, it's too loud. You can just swap the back box, no problem. My original plan was to keep the afterburner system and just change the backbox for track days.

You could go full afterburner decate system and use a STI or prodrive backbox to bring the noise right down

Ok thanks. I want a little more noise than standard so was thinking ninja2 or miltek backbox after a decat. Still too loud for motorway miles?

I had a look under the car and it seems that I have a down pipe and then a short pipe before the central afterburner section. Do they both have cats in on a JDM?

You will need to remap the car if you go decat, if you go sports cat you will also need to remap the car, so its a no win situation, its best just leaving the standard cat on, saves lots of hassle come mot time ;)

Tony:)

Thanks Tony,

I'm pretty set on the remap anyway so the decat seems logical. I'm not worried about the MOT. I just need to know if there are 2 cats or just one in the downpipe?

What do other people call the other pipe- is it a mid pipe?

Just want to say thanks, you've ended up answering a lot of my JDM questions so far and now I'm a very happy owner of a great JDM STI 03. its such a different car to my uk classic I cant quite believe it. Grinning from ear to ear.:luxhello:

You only have one in the down pipe AFAIK. I also have a jdm sti and love the extras like the rear wiper and folding mirrors. If your changing the exhaust you might as well swap the whole lot for a 3" system anyway, this will future proof you for inevitable "Im going for 400+" lol

My car was running 420bhp / 406ft lbs with the cat in the down pipes, no restriction caused, to quieten it down we cut the tail section 3" pipe off (108db @ 4,800rpm > track days where a :nono: ) and installed a 2.5" tail section, now running at 102db & no loss of power at all :D

Keep the cat & concentrate on the tail section to take care of the noise :thumb:

Alright mate!
The factory downpipe is two sections with one or two cats in it but a decat downpipe will be one section and replace both bits so it doesn't matter how many cats you had, you will be left catless.
http://img154.imageshack.us/img154/8...iagram22nd.gif

Oh and the backbox has hardly any effect on power

Hi Toffee,

I'm afraid that I don't understand what you mean by no restriction being caused. Almost everything I have read (not taking it all as gospel) and looked at suggest that the cats will cause a restriction due to the exhaust gas not being able to flow as easily. I've no doubt that you have a sweet ride (420bhp / 406ft lbs) but for me I would gain more power by removing the cats and having a remap no?:freak3::wonder:

Ok, thanks dude, that makes sense. Wasn't sure if I would have to buy two pipes or just the one. Right who wants to sell me a down pipe then??

What's the retail on a second hand one then. Should I look afterburner so that it fits with my centre pipe?:)

Your centre section is a probably 2.5" so any bellmouth to 2.5" down pipe will do the job.
I got a Japspeed one on ebay for £60 new.
Might as well get some new gaskets while your at it.

yup, 2.5. 60 quid!! awesome. I just need a buyer for that apexi and its remap time.

nice

Sorry i meant i got mine off ebay for £60. I don't have one for sale at the moment but there are shed loads out there.


Oh and you should change your avatar now to an sti :thumb:

didn't think you had one. That's a great price. I'm gonna check out ebay more carefully but they look double the price.

I'll try with the avatar. Hmmm

Toffee failed to mention that he has sport cats.... not OE cats which is what you're referring to. ;)

Removing the OE cats on the JDM is a great way to unleash more go go. The choice is simple imo, either remove the OE cat's (decat) or fit a sports cat.

If you are replacing the whole exhaust why not go 3".
This one on ebay is for 3" but its only on £18 with 4 hours to go:
http://www.ebay.co.uk/itm/GD-SUBARU-...item2c6079c1a4

Probably not a good idea as its not twin scroll ;)

Tony:)

no need for 3 inch. Only if its cheaper but then don't I have to find a 3" back box to match it to or can I get some sort of 2.5 to 3 adapter.

Thanks Tony. Does the down pipe have to be specifically twin scroll? How is it different? I know you said leave it but I'd appreciate the help.

John

The dp for a Newage Twinscroll JDM MUST BE a twinscroll dp. The UK ones for the same year are single scroll and the shape of the flange to the turbo is totally different and won't fit.

Thanks Shaun, needed to know that. Any idea on makes or brands? I'd prefer to pick up a cheaper second hand one if I can but I guess they might be quite rare.

oops yeah sorry mate. forgot about about your twinscrollyness.