Discussion
Guys, bit the bullet and purchased a sports cat down pipe for my 2005 WRX wagon. It's a 3inch system. I have a Prodrive back box, so now needing a centre section.
Now I suspect my back box is 2.5 inch, so if I dropped to a 2.5 centre section would this mate to my 3 inch down pipe?
Been looking at some cat back systems on the bay, 3 inch and reasonably priced. However some of the 2.5 inch centre sects are fairly cheap.
Also, what's your thoughts on mapping with a sports CAT, does it need mapped, is it likely to det? I know a map would release the potential, and will no doubt go down that route, but maybe not right away.
Decisions decisions.
Now I suspect my back box is 2.5 inch, so if I dropped to a 2.5 centre section would this mate to my 3 inch down pipe?
Been looking at some cat back systems on the bay, 3 inch and reasonably priced. However some of the 2.5 inch centre sects are fairly cheap.
Also, what's your thoughts on mapping with a sports CAT, does it need mapped, is it likely to det? I know a map would release the potential, and will no doubt go down that route, but maybe not right away.
Decisions decisions.
IMHO a Prodrive sports cat or the factory cat is the way forward for emissions. Aftermarket sports cats are usually 100cell-200cell density. I have a 100cell cat on mine and it's a pile of rubbish!! Completely useless for emissions purposes. You should maybe have left the factory downpipe on and just decatted the uppipe and scrubber pipe with stainless steel items. That's enough to squeeze the max from a TD04 turbo
As far as stainless steel exhausts are concerned sticking to the OE diameter would have been the easiest way forward. Still makes a lovely sound and releases all the power you're ever going to make from the standard turbo but crucially mates up to the factory downpipe without issues.
Hayward & Scott or Miltek 2.5/8" diameter exhausts are manufactured to match factory systems in diameter and flange positioning. The only way you're going mate 3" to factory piping is with an adapter or cut and weld a 3" flange to your factory pipe like i did for my GrpN backbox.
As for mapping.....You will see overboost from exhaust mods. That in turn could cause detting if there is too much overboost. Mapping doesn't just release power from your mods but makes sure it all runs as it should.
As far as stainless steel exhausts are concerned sticking to the OE diameter would have been the easiest way forward. Still makes a lovely sound and releases all the power you're ever going to make from the standard turbo but crucially mates up to the factory downpipe without issues.
Hayward & Scott or Miltek 2.5/8" diameter exhausts are manufactured to match factory systems in diameter and flange positioning. The only way you're going mate 3" to factory piping is with an adapter or cut and weld a 3" flange to your factory pipe like i did for my GrpN backbox.
As for mapping.....You will see overboost from exhaust mods. That in turn could cause detting if there is too much overboost. Mapping doesn't just release power from your mods but makes sure it all runs as it should.
I got the sports cat fairly cheap. Was not fussed one way or the other with a 2.5 or 3 inch ! Had a full 3 inch on my WRX several years ago, and could not find fault with it.
Not looking for big power either, as I have my supercharged Elise for that, would just be looking for smooth running and a bit more oomph than I have the now. 260-270 would suffice.
Looking like a full 3 inch now then.
Not looking for big power either, as I have my supercharged Elise for that, would just be looking for smooth running and a bit more oomph than I have the now. 260-270 would suffice.
Looking like a full 3 inch now then.
DC5TEG said:
Francis. Is it likely to pass an emissions test with 100 cel sports cat and the remaining cat left?
Many years ago when I had my first decatted scoob, the consensus was that it would get through the emissions with the one cat? Is this rubbish?
In my experience not with a 100Cell cat. The one on mine is useless and may as well be decat so i'm going to be chopping my downpipe and replacing the cat with a straight through bit of SS 3" pipe. It would be more effective to stuff an old pair of underpants up there..lol..Many years ago when I had my first decatted scoob, the consensus was that it would get through the emissions with the one cat? Is this rubbish?
So 100Cell Cats are a waste of time. If you can find one that works good luck to you. I'd have said you need something like a 300+cell cat to get through emissions. I've no idea what the Prodrive Cat density is, all i know is it works.
You could just say fudge it and go completely decat. Keep your old exhaust system so when it comes to MOT time you can just swap it back temporarily.
I have a 100cell cat on mine and it flew through its first MOT when it was new but like all cats it will deteriorate over time and it is getting more difficult to get through emission’s these days. Watching the countdown on the clock makes me sweat. I have been lucky so far but it may not go through next time.
If its new I would say you would be ok the first 1-2 mots but after that it will be a matter of luck I think!
If its new I would say you would be ok the first 1-2 mots but after that it will be a matter of luck I think!
allsop83 said:
I would reccomend you stick with 2.5" system- 3" is too big unless you are planning a 400bhp build, it won't do your spool any favours.
Totally disagree. As above, I had a full 3 inch system on my WRX back in 2004, spool up was fantastic comparing with standard, and the car was totally transformed. And that was running 257bhp before the remap. I done a load of SIDC / Scoobynet runs back then and plenty of the guys were running 3inch systems with under 300 ponies. So are you talking from a personal experience or what someone said on a forum.?A lot of people go for the 3" because the bigger diameter pipe makes a bigger noise and it sounds better when you say you have 3". 
That's really all you're getting over a standard OEM diameter exhaust pipe which will be good for 350bhp anyway. When you go the next step with a bigger turbo, injectors etc...then get a bigger diameter system.
Same for the standard headers and uppipe. With a bit of porting of the headers, porting your heads exhaust ports (making the ports concentric because they aren't as standard), and welding and porting of the standard uppipe(STi) makes it all good for 350bhp and will promote early/quick spoolup. Also best setup for maximising torque on the standard turbo setup.
Change to a bigger diameter uppipe and swap to tubular headers on something like a VF35 and you will see slower and later spooling making for a laggy feeling turbo. VF35's aren't laggy on the standard piping so why introduce lag.
Bigger isn't always best.
That's really all you're getting over a standard OEM diameter exhaust pipe which will be good for 350bhp anyway. When you go the next step with a bigger turbo, injectors etc...then get a bigger diameter system.
Same for the standard headers and uppipe. With a bit of porting of the headers, porting your heads exhaust ports (making the ports concentric because they aren't as standard), and welding and porting of the standard uppipe(STi) makes it all good for 350bhp and will promote early/quick spoolup. Also best setup for maximising torque on the standard turbo setup.
Change to a bigger diameter uppipe and swap to tubular headers on something like a VF35 and you will see slower and later spooling making for a laggy feeling turbo. VF35's aren't laggy on the standard piping so why introduce lag.
Bigger isn't always best.
Thread revival.
Just for information for fellow PHs, my remapped scoob with 100 cel sports cat, flew through emissions at MOT. I was quite worried about it getting through, but results were spot on!
Rear struts/springs also done, then got called away to work. So fronts and alignment to be carried out shortly. Managed to drill out my snapped strut top mount bolt, replaced with a fresh, worked out fine.
Car sits nice 30mm lower.
Just for information for fellow PHs, my remapped scoob with 100 cel sports cat, flew through emissions at MOT. I was quite worried about it getting through, but results were spot on!
Rear struts/springs also done, then got called away to work. So fronts and alignment to be carried out shortly. Managed to drill out my snapped strut top mount bolt, replaced with a fresh, worked out fine.
Car sits nice 30mm lower.
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