More noise/ decat


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Jul 31, 2011
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i have a 1.8 turbo a3 with a tip, forge diverter valve & a cat back miltek exhaust, thinking of fitting a decat pipe, just wondering will this result in lights coming up on the dash due to the cat being removed?? & will this make a big difference to the noise of exhaust, any feedback would be great :)
What engine code? I know that on an AGU no EML will come up but others will and need to be mapped out... in my experience the decat gave it a slightly deeper grunt when putting the foot down.
if your cars got one 02 sensor then you want get no lights on the dash. it'll make it a little louder but defo will change the tone of your exhaust. i've got a downpipe and decat on a cat back sebring exhaust and my car sounds exactly like a astra vxr with pops and bangs as well
Basically jus a bit deeper tone on the exhaust. And the only lights i get on my agu is a lil flame at gear changes over 2k revs or bleeping the throttle over 2k :)
On my agu the downpipe and decat worked great and didn't cost the earth unlike my ko4 one I need lol, to me it isn't about sound but freeing up those extra horses in the engine and it's a great mod just keep ur cat, but would help if when u post u write ur engine the year of ur car mate, and also has the car been remapped as it would really benefit from this if u have added all these bits or planning to fit more
mine made a little more turbo noise when fitted, nothing noticeable on the exhaust note tho, that was with a std cat back system,

drove mine for around 1.5kmiles before i had it mapped and did not bring up a light on the dash (aum with 2 sensors)
i did get a fault code when scanned with vagcom though
sorry mate its a 1998, 1.8 turbo 150bhp model, agu engine code i think? the car is not mapped i dont think it will get remapped i just replaced clutch & flywheel & then read up the standard clutch wouldnt cope with remapped power so that wont be getting done lol, thats good i dont want too much noise just a bit more grunt would be good :) Just didnt wanna remove the cat if it was gonna cause lights to come up etc with cat being removed, thanks for all the feedback guys!
This looks like an ideal time for me to jump in with a new question as i have been toying with the idea of new exhausts, decats, sportscats, and downpipes but what i want to know is whats MOT legal as cant be doing with faffing about swapping stuff over just to get thru the test.
Who told u standard clutch can't handle a remap???? Nonsense the standard clutch can handle a great deal of power I'm running stage 2 mate and over 220 bhp and still on the original clutch and will be using it on my ko4 conversion, trust me the clutch can handle it
on the agu the light wont come up, as for the clutch - you should easily be able to handle 180-190bhp from the stage 1 map.
Vrbob the downpipe will be fine and less restrictive then standard but if u don't want the hassle of changing bits over for the mot every year the I suggest u buy a sports cat and downpipe kit perhaps a 200 cel one and ur shouldn't have any problem just be warned if its too cheap then be careful as I have seen issues with cheap sports cats before, miltek do great kits depends on ur budget mate or find a kit on eBay hope this helps I'm running a decat and downpipe and had no issues ever
Cheers Mate looks like your becoming an 8L expert V fast :)

So i could get a bigger downpipe fitted (yeah i know its a b1tch on the S3) and it will be MOT friendly. Is it only if you Decat completly that you would fail then? As could the downpipe be used in conjunction with just a cat back exhaust or does this defeat the purpose of trying to free up flow of gases keeping the cat?

what i am ultimatly trying to work out is if it is possible to go to stage 2 and stay legal and get somewhere towards the 300bhp range on a standard K04. As this might be something i think about in future so i want any modifications i do to be moving in that direction if possible when funds allow.
U can stay legal mate relentless sell a 3" downpipe and decat or if U wish a sports cat fitted for a good price but a decat would be better if u want to hit 300bhp I'm soon to start my ko4 I'm looki g for a good 260 bhp upwards, anything 300bhp and above then will have to change rods and other bits, I'm no expert yet lol just researched alot and listened and chatted to the right people and don't want make any mistakes or see people lose or waste money where they don't need to lol
for the record its 300ftlbs on 300bhp when rods become the weak point, which also depends on engine code..

get a 100 or 200 cell cat, and to be fair swapping the cat once a year for all of a few hours its much loss when you have a nice clean 300hp with a really nice sounding exhuast
So if this is the case whats best to do first? eg best bang for the money

Oh and not looking to push the rods etc in my car so would be happy with a reliable 280ish bhp
Just do the bits u want piece by piece just like u I'm heading down the same route of at least 280bhp, got bits all ready just downpipe and decat left and new intercooler set up as I can't use my forge one !
Well then i think my plan is to go for bargain hunts then and see what i can acquire cheapish as and when.
as mentioned just buy bit by bit if you cant fork out in one go.

im buying fmic and tip first, decat and downpipe and system all made in one go. then remapped
then much later on likley start of next year start building up a bt project to add to what i have, injectors,gt2871r and manifold,
but as the turbo and injectors are the last thing i can have the decat flange change likley to a v band. then remapped to add on to what i have

then hopefully aim for the 300hp mark but keep figures on the lean side because although i have a ajl engine which is same as the aeb still limited to 300ftlb to be reliable. any one know what bhp that corresponds to or is that all down to the tune/fueling/ignition
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