john_mchutchison Posted June 19, 2012 Share Posted June 19, 2012 Im thinking of getting a decat centre section for MY55 STI but im worried it might need a trip to Andy Forrest or some other tuner, is this correct? Currently it has the prodrive centre section and an afterburner back box if this matters, cheers for any advice. Hutch Link to comment
adz_wrx Posted June 19, 2012 Share Posted June 19, 2012 I would say so! If nothing else it'll give you a very annoying EML light until you get it mapped for emissions. Link to comment
john_mchutchison Posted June 19, 2012 Author Share Posted June 19, 2012 (edited) The light wont bother me but will it cause any damage or just fail an emmisions test? i had this set up on MY03 WRX without any issues. Edited June 19, 2012 by hutch1973 Link to comment
badbaz Posted June 19, 2012 Share Posted June 19, 2012 Centre cat can be removed without worry John - is the 'prodrive' centre pipe not an upgrade anyway? Link to comment
john_mchutchison Posted June 19, 2012 Author Share Posted June 19, 2012 I would have thought a decat section would be better than the prodrive?? maybe someone can shed some light on this. Link to comment
badbaz Posted June 19, 2012 Share Posted June 19, 2012 What's the reason for remove it John? Link to comment
john_mchutchison Posted June 19, 2012 Author Share Posted June 19, 2012 (edited) More power more noise, isnt that what were all after??? Long plan is for full decat and trip to Andy Forrest for stage 2 remap Edited June 19, 2012 by hutch1973 Link to comment
gus the bus Posted June 19, 2012 Share Posted June 19, 2012 I would have thought a decat section would be better than the prodrive?? maybe someone can shed some light on this. I thought there wasn't a cat in the centre section just a resonator box. the cat is in the "cat pipe" between the centre section and downpipe IIR. In the blobeye the cat pipe used to be replaced by a decat pipe as part of the Prodrive upgrade and just the heatshields refitted. Caught a few folk out at the time Is yours a Hawkeye John? Gus Link to comment
mctwistuk Posted June 19, 2012 Share Posted June 19, 2012 Centre is resonated in blob and hawk eyes and then there is a cat between centre and downpipe then cat in downpipe. Removing cat between centre and downpipe will apparently still pass Mot whilst freeing up a very small increase in power but gives mire of that loved burble. Chris Link to comment
john_mchutchison Posted June 19, 2012 Author Share Posted June 19, 2012 Gus mine is a blob. Looks like there is 4 parts to exhaust, as Gus says no cat in "centre section" only in the part inbetween the centre section and down pipe. So if i want to decat 1 part it has to that part, im glad i didnt oreder centre section. Is the prodrive part in the centre section?? Link to comment
gus the bus Posted June 19, 2012 Share Posted June 19, 2012 Gus mine is a blob. Looks like there is 4 parts to exhaust, as Gus says no cat in "centre section" only in the part inbetween the centre section and down pipe. So if i want to decat 1 part it has to that part, im glad i didnt oreder centre section. Is the prodrive part in the centre section?? John, if you have Prodrive (PPP) then the cat pipe ( bit between the centre section and downpipe) has already been replaced with a straight through pipe and the heat shields refitted. Its this that caught a few folk out thinking it was still standard. If you just want more burble and the original centre section with resonator box is still on then replace it with a straight through (de-resonated) section Link to comment
badbaz Posted June 20, 2012 Share Posted June 20, 2012 Glad we are getting somewhere here - I released a good burble by removing the 2nd cat, fitted a straight through centre and a Ninja II silencer when I got my car way back when You're not gonna notice any power increases unless you get downpipe out and remap etc Link to comment
C_WRX Posted June 20, 2012 Share Posted June 20, 2012 (edited) I remember all this kinda thing when first got my WRX blob too. Fitted centre section first and never got it remapped, no real power difference although car felt a little smoother / free'er. Sure I've still got a centre section decat pipe somewhere from when I got the extra piece of pipework still attached when bought the sportscat dp . Remembered this diagram (which I can't get to copy on here so link with it on it will have to do) http://www.scoobyworld.co.uk/catalog/product_info.php?cPath=24_53&products_id=448 Edited June 20, 2012 by C_WRX Link to comment
arch Posted June 20, 2012 Share Posted June 20, 2012 The following might help with the understanding of how the system works. The diagram below is of a newage WRX inlet and exhaust. The only difference with the STI is it has no cat in the up-pipe. The cat in the uppipe is critical as it causes a significant restriction with the gas flow to the turbine. Given that the speed and flow of gases to the turbine are what determines how quickly the turbine speed increases and how fast it rotates and hence how quickly the turbo spools, its not hard to see that any restriction in the uppipe will have significant effects on spool. The way the gases are delivered to the turbine has to be the single biggest facter affecting spool. This is one reason why the twin scroll set ups and front mounted turbo instal's have superior spool. The image below shows the newage STI PPP which consists of the Prodrive sports cat to remove some of the restriction in the downpipe while remaining MOT friendly. (This is the only cat I have on my blobeye and it passes MOT's with ease). It also has a cat delete pipe for the pipe they term the midpipe, an uprated fuel pump and an ECU remap to reflect the changes. Compare that to the WRX PPP which has only the midpipe cat delete, a silicon intercooler hose and an ECU remap and its easy to see why the WRX PPP is poor value for money. Link to comment
john_mchutchison Posted June 20, 2012 Author Share Posted June 20, 2012 Great info guys and advice, thx a lot. It seems like ill have to save my pennies then and get the full thing decatted and remapped to make any great difference, glad i didnt buy that centre section last night. Hutch Link to comment
fai17 Posted June 21, 2012 Share Posted June 21, 2012 I'm glad that Archie and Gus cleared that up. On a Sti there is just a cat in the down pipe. Best vfm is to save up and decat and straight through system along with a remap to suit. Done it once in a job lot rather than bits here and there. Link to comment
man-with-men Posted June 21, 2012 Share Posted June 21, 2012 Save your money, keep it standard, put better pads on it, drive it harder. The end Link to comment
badbaz Posted June 21, 2012 Share Posted June 21, 2012 On a Sti there is just a cat in the down pipe. Not true Peter - there are two cats, downpipe and next pipe Link to comment
man-with-men Posted June 21, 2012 Share Posted June 21, 2012 peter doesnt know what hes on about Link to comment
badbaz Posted June 21, 2012 Share Posted June 21, 2012 peter doesnt know what hes on about Link to comment
fai17 Posted June 22, 2012 Share Posted June 22, 2012 Not true Peter - there are two cats, downpipe and next pipe I like your description. Next pipe and the after pipe Link to comment
jae Posted June 27, 2012 Share Posted June 27, 2012 Sorry to hijack the thread but just to expand on this question a bit, I have a UK300 which is *just* a WRX however it's been decatted at the centre section and I have the decat for downpipe and up pipe to go on. When these go on I suspect the CEL will be on? Is there, by going from the diagram above, a 02 sensor in the up pipe and if so what do I do with it if the decat doesn't have a boss for it? Will it NEED to be mapped, currently not looking for the extra grunt but a bit more sound. Thanks and sorry for the hijack again. Link to comment
The Don Posted June 27, 2012 Share Posted June 27, 2012 Sorry to hijack the thread but just to expand on this question a bit, I have a UK300 which is *just* a WRX however it's been decatted at the centre section and I have the decat for downpipe and up pipe to go on. When these go on I suspect the CEL will be on? Is there, by going from the diagram above, a 02 sensor in the up pipe and if so what do I do with it if the decat doesn't have a boss for it? Will it NEED to be mapped, currently not looking for the extra grunt but a bit more sound. Thanks and sorry for the hijack again. The A/F sensor (wideband O2) is in the manifold, just before the up pipe. Only item in the up pipe (apart from the pre-cat) is the EGT sensor which if not replaced can be mapped out or you can use the 2.2K ohm resistor fix for cel. Link to comment
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