Sports cat - downpipe or centerpipe?
14 April 2009, 07:56 PM
#1
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Sports cat - downpipe or centerpipe?
Hi,
looking for opinions - which solutions is better - sports fast flow cat in downpipe (100 cells) or in center pipe (100? 200 cells?)
Which is better in terms of power of course, but also to stay legal and have peace of mind with car tests...
cheers
looking for opinions - which solutions is better - sports fast flow cat in downpipe (100 cells) or in center pipe (100? 200 cells?)
Which is better in terms of power of course, but also to stay legal and have peace of mind with car tests...
cheers
14 April 2009, 08:14 PM
#2
The critical post-turbo part of the exhuast system is the area immediately after turbo i.e. the downpipe. The least restrictive this is to airflow, then the greater the gains to be had (this is why decatting is so effective).
So by that rationale, if you intend to keep one of the cats, then keep the centre one. Therefore, replace the downpipe with the 100-cell sports cat.
Scooby World's Ninja one is supposed to work okay...
So by that rationale, if you intend to keep one of the cats, then keep the centre one. Therefore, replace the downpipe with the 100-cell sports cat.
Scooby World's Ninja one is supposed to work okay...
Last edited by joz8968; 14 April 2009 at 08:16 PM.
14 April 2009, 08:34 PM
#3
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A cat works better the hotter it is. By that logic, if you're going to put a cat in, put it where it will do the best work - in the downpipe. Mine sailed through MOTs and it didn't restrict power in the mid 300s.
15 April 2009, 12:12 AM
#6
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Yes that's what I mean. A classic will pass with just a sports cat in the downpipe and nothing else. I know, because I've done it three years in a row, no 'friendly testers' required.
15 April 2009, 10:56 AM
#7
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Of course I understand that it needs to be hot, so I also know that for a test the one in centerpipe should be warmed up a bit - what actually shouldn't be a problem.
Isn't anyway cat in down pipe more restricting, right after turbo, than the one in center pipe? That's the main case
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15 April 2009, 11:07 AM
#8
Sorry Ami, I thought you wanted to keep one of the OEM cats and subs. the other with a 100-cell cat, hence my original advice.
If you want to throw away one of the cats then the logical move would be to totally decat the downpipe and have a 100-cell cat in the centre... BUT... I don't think it'll be big/get hot enough (being further away from the turbo) to get you through the emissions
.
Personally, I'd do as 99gw says and get a 100-cell d/p and run a totally decated centre. The d/p should defo get you through the MOT and is almost as free flowing as a full decat - so you only lose out on a few bhp, anyway (I think).
If you want to throw away one of the cats then the logical move would be to totally decat the downpipe and have a 100-cell cat in the centre... BUT... I don't think it'll be big/get hot enough (being further away from the turbo) to get you through the emissions
.Personally, I'd do as 99gw says and get a 100-cell d/p and run a totally decated centre. The d/p should defo get you through the MOT and is almost as free flowing as a full decat - so you only lose out on a few bhp, anyway (I think).
Last edited by joz8968; 15 April 2009 at 11:08 AM.
15 April 2009, 05:46 PM
#9
Sorry Ami, I thought you wanted to keep one of the OEM cats and subs. the other with a 100-cell cat, hence my original advice.
If you want to throw away one of the cats then the logical move would be to totally decat the downpipe and have a 100-cell cat in the centre... BUT... I don't think it'll be big/get hot enough (being further away from the turbo) to get you through the emissions.
Personally, I'd do as 99gw says and get a 100-cell d/p and run a totally decated centre. The d/p should defo get you through the MOT and is almost as free flowing as a full decat - so you only lose out on a few bhp, anyway (I think).
If you want to throw away one of the cats then the logical move would be to totally decat the downpipe and have a 100-cell cat in the centre... BUT... I don't think it'll be big/get hot enough (being further away from the turbo) to get you through the emissions
.Personally, I'd do as 99gw says and get a 100-cell d/p and run a totally decated centre. The d/p should defo get you through the MOT and is almost as free flowing as a full decat - so you only lose out on a few bhp, anyway (I think).
15 April 2009, 06:11 PM
#10
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my 100 cel aint passed an mot yet
...keep having to swap to ome one but next time am going to put centre cat back in see if it passes, just easier to change..still weary of vosa road side cheaks
...keep having to swap to ome one but next time am going to put centre cat back in see if it passes, just easier to change..still weary of vosa road side cheaks
15 April 2009, 06:16 PM
#11
Sorry Ami, I thought you wanted to keep one of the OEM cats and subs. the other with a 100-cell cat, hence my original advice.
If you want to throw away one of the cats then the logical move would be to totally decat the downpipe and have a 100-cell cat in the centre... BUT... I don't think it'll be big/get hot enough (being further away from the turbo) to get you through the emissions.
Personally, I'd do as 99gw says and get a 100-cell d/p and run a totally decated centre. The d/p should defo get you through the MOT and is almost as free flowing as a full decat - so you only lose out on a few bhp, anyway (I think).
If you want to throw away one of the cats then the logical move would be to totally decat the downpipe and have a 100-cell cat in the centre... BUT... I don't think it'll be big/get hot enough (being further away from the turbo) to get you through the emissions
.Personally, I'd do as 99gw says and get a 100-cell d/p and run a totally decated centre. The d/p should defo get you through the MOT and is almost as free flowing as a full decat - so you only lose out on a few bhp, anyway (I think).
15 April 2009, 06:30 PM
#12
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Yeah, I was actually thinking rather about center pipe, where gas flow is anyway a bit slower.
why btw you say twin-scroll likes a bit of back pressure?
why btw you say twin-scroll likes a bit of back pressure?
15 April 2009, 09:51 PM
#14
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Once you start to modify an 03 WRX you should decat the up pipe anyway. Stops it disintegrating and going through the turbo. I have the TSL Thundercat downpipe, i have had it on for years and have always passed the MOT. Another two weeks and i will hopefully pass another! LOL
15 April 2009, 11:12 PM
#15
That would seriously hack me off. 
That's why I went full decat - I can tolerate the 1/365th of the year the cat is put back on for MOT time...
Has anyone actually had a roadside check?
If it fails, what 'punishment' are the rozzers lawfully bound to dish out?
That's why I went full decat - I can tolerate the 1/365th of the year the cat is put back on for MOT time...Has anyone actually had a roadside check?
If it fails, what 'punishment' are the rozzers lawfully bound to dish out?
16 April 2009, 12:12 AM
#16
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mmmm i dont know wat punishment is but il ask my dad to ask vosa next time they come cheak at bus garage.....and yes it is annoying wen i have to take cat off but just dont work on my car....
mind you some of them road side jobbies use ANPR so if you car lidgit wen it gose past they prob wont pull you in anyway...i see alot of taxis, vans and shoddy looking cars etc ready for being towed away as they do it near were i live often....
....mind you some of them road side jobbies use ANPR so if you car lidgit wen it gose past they prob wont pull you in anyway...i see alot of taxis, vans and shoddy looking cars etc ready for being towed away as they do it near were i live often....
16 April 2009, 05:23 PM
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near halfords on bradford road...old vw garage but recently been knocked down but still...sure seen them on leeds road too, drive a van all day round hudds so see alot
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