You can change the style the forum displays by selecting your preferred style at the bottom left of the site.
We have made an enhancement so that old threads should now link from search results to the correct thread. This is not yet in place for single post links
So what's your advice? I can get a 3" stainless exhaust system for my '93 100 S4 from two different suppliers for a similar price but one includes a fitted race cat and the other comes without a cat fitted but with a small cat that can be fitted for the MOT. Now I don't really mind the thought of putting the cat on and off once a year but is there really any performance advantage in not having a cat fitted? In theory with no cats there should be less restriction but I read somewhere that on a turbo car a cat will actually help straighten the swirling exhaust gases that exit the turbo so therefore having a permanent cat in place would really be the best performance option! What do you reckon?
'93 S4 Avant now back on the road complete with new shiny go faster bits.
If you have a big turbo in the future and go for more hp then a bigger sport/non cats exhaust is needed , for a standard engine , i think its good for start .i changed my exhaust on an standard RS2 and didn,t notticed any power increace {there will be a on the RR}. the sound of the 5 cilinder you will love tho.
I noticed a big difference when I removed my cats.The engine just felt so much more willing.
De cat every time in my book....
Cheers,
Steve.
The Perfectionist
sigpic
Audi Class Concours winner Stoner Park 2014, ADI Concours D'Elegance Class Winner 2008, Runner up 2014. Winner, S2Forum Show'n'Shine Billing 2006 & 2008.
CATs are quite restrictive on turbo engines. For full out performance - especially on bigger turbos they are not recommended. However, to keep legal of course a CAT is needed on all UK cars registered after Sep 1992 (iirc). Some folk like to fit the CAT just in time for MOT or take it places that turn a blind eye if the face fits.
I think the best compromise is to use a race CAT in place of the factory items. The stock CATs on the S2 and UrS4 are restrictive ceramic affairs whereas the motorpsort variety of CATs are a metallic design and are much less restrictive. Such CATs are used on WRC cars putting out silly amounts of torque so they are up to the job from a performance PoV - and you stay legal all year round.
P.S. The exhaust is a little louder without Cats, but sounds fantastic with popping on overrun and a really nice 5 cyl burble..
The Perfectionist
sigpic
Audi Class Concours winner Stoner Park 2014, ADI Concours D'Elegance Class Winner 2008, Runner up 2014. Winner, S2Forum Show'n'Shine Billing 2006 & 2008.
CATs are quite restrictive on turbo engines. For full out performance - especially on bigger turbos they are not recommended. However, to keep legal of course a CAT is needed on all UK cars registered after Sep 1992 (iirc). Some folk like to fit the CAT just in time for MOT or take it places that turn a blind eye if the face fits.
I think the best compromise is to use a race CAT in place of the factory items. The stock CATs on the S2 and UrS4 are restrictive ceramic affairs whereas the motorpsort variety of CATs are a metallic design and are much less restrictive. Such CATs are used on WRC cars putting out silly amounts of torque so they are up to the job from a performance PoV - and you stay legal all year round.
You sure about all that...... I was under the impression that it was a bit more complicated than that!
I thought Pre '92 was just standard emissions requirements
Post Aug '92 they must meet 'CAT' Requirements, but having the actual cats is not mandatory,
Post Aug '94 much more stringent requirements - VERY difficult to pass without an actual CAT being present
CAT test is an unfortunate term which leads many to think that the MOT is testing the Catalytic converter fitted to later vehicles but this is not so.
and from the other big mot website
Originally posted by MOTTESTER.CO.UK
There is no necessity to have a catalytic converter on any vehicle. However, your vehicle will be MOT Tested as if it had one and it is unlikely that it will pass the emissions part of the MOT without the cat. The reason being that the engine and the catalytic converter were all part of the same integral design to meet the emission requirements when the vehicle was manufactured - MOTT.
CAT test is an unfortunate term which leads many to think that the MOT is testing the Catalytic converter fitted to later vehicles but this is not so.
The MOT is testing emissions, so if the emissions from the tailpipe meet the requirements the vehicle passes. Whether a CAT is fitted is irrelevant. The deciding factor is the vehicles date of first registration. A "Cat" may be fitted to a vehicle which only needs to meet the two gas test and if the emissions are satisfactory, it passes. A "Cat" may have been removed and the vehicle is required to meet the "Cat" test standard by virtue of its first registration date. If the emissions meet the standard then it passes.
Many advanced design engines will meet the "Cat" requirements with a standard exhaust but of course may be emitting other pollutants not subject to the MOT.
Fantastic find
Mark
Race Clio RS197
S2 Coupe ABY (Green) - RIP
S2 Coupe ABY (Blue) - Sold
You sure about all that...... I was under the impression that it was a bit more complicated than that!
I thought Pre '92 was just standard emissions requirements
Post Aug '92 they must meet 'CAT' Requirements, but having the actual cats is not mandatory,
Post Aug '94 much more stringent requirements including the actual presence of the CAT.
Yes, if the car is registered after August 31st 1992 and has a cat fitted as standard out of the factory, you cannot legally remove the cat and pass an MOT test. Of course if the car doesn't have a CAT standard then it will pass.
The MOT test is actually dated on the year of the engine and not the year of car.
........ a cat fitted as standard out of the factory, you cannot legally remove the cat and pass an MOT test.
Well that goes against all the info I've found so far ....... I reckon it's just you ABYers getting jealous of our superior firepower and propogating urban myths to make yourselves feel better!
You need a CAT to pass the emissions test from post-92 I think?
Another reason why the 91 3B is superior
With a de-cat and a decent full exhaust, you certainly get a bit more noise, you definitely get more of a "whooshing angry hissing" on full boost, which is nice, and you get a lot more popping and burbling on the overrun, which is lovely. Quite often you get flames
Ex S2 owner, now running around in an A4 Avant quattro...
We process personal data about users of our site, through the use of cookies and other technologies, to deliver our services, personalize advertising, and to analyze site activity. We may share certain information about our users with our advertising and analytics partners. For additional details, refer to our Privacy Policy.
By clicking "I AGREE" below, you agree to our Privacy Policy and our personal data processing and cookie practices as described therein. You also acknowledge that this forum may be hosted outside your country and you consent to the collection, storage, and processing of your data in the country where this forum is hosted.
So what's your advice? I can get a 3" stainless exhaust system for my '93 100 S4 from two different suppliers for a similar price but one includes a fitted race cat and the other comes without a cat fitted but with a small cat that can be fitted for the MOT. Now I don't really mind the thought of putting the cat on and off once a year but is there really any performance advantage in not having a cat fitted? In theory with no cats there should be less restriction but I read somewhere that on a turbo car a cat will actually help straighten the swirling exhaust gases that exit the turbo so therefore having a permanent cat in place would really be the best performance option! What do you reckon? 
If you have a big turbo in the future and go for more hp then a bigger sport/non cats exhaust is needed , for a standard engine , i think its good for start .i changed my exhaust on an standard RS2 and didn,t notticed any power increace {there will be a on the RR}. the sound of the 5 cilinder you will love tho. 
Comment