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Sports Cats 100 Cell Vs 200 Cell on S4 B6 - Anyone have any experience with emissions and the law?

Les.Tansey Dec 7, 2020


What Cell Sports Cat for Audi S4 B6 can I get away with?

Poll closed Feb 7, 2021.
  1. 100 Cell

    0 vote(s)
  2. 200 Cell

    0 vote(s)
Multiple votes are allowed.
  1. Les.Tansey

    Les.Tansey New Member

    Hi All,

    So I've just fitted a Milltek Non Resonated Cat Back exhaust to my B6 S4 Avant. It sounds good, but I did just want a little more volume and rasp. So naturally my first option was to look at Milltek decat downpipes, but it's my daily, and I don't want to be getting pulled over for excessive noise and smell and not having cats fitted to my car - for me this would somewhat spoil my enjoyment of the car.

    However, if I was pulled over and inspected for being loud and smelly but I could just get by because I have cats futted and I just fall within the emissions guidlines for the car, then it wouldn't bother me so much. I can be like 'search me, its all Kosher' and then I can crack on with my day without any further bother.

    So naturally, I like the idea of 100 cell catalytic convertors so I can try and have the best of both worlds. So I would love to know; has anyone ran 100 cell cats on there S4 B6? And did your car pass the emissions tests/mot?

    I've heard that 100 cell cats are more for the track, but yet I have seen them sold as 'Road Legal' too from half reputable looking companies? I just wondered if anyone has already tried and tested this combination with success? Or if I could get any tips on this?

    Does anyone know how many cell the standard S4 B6 cats are out of interest? 400 cell? 600 cell even?

    I want maximum exhaust flow, whilst just keeping within the law. I want the extra growl and the miniscule power increase too, but also a very very light overrun crackle mapping into the car. So based on the advise of the mapper I'm most likely using (Unicorn Motor Developments, in Stockport), the lower the cell rating of the cat, the more durable it will be in conjunction with the overrun (which will only be subtle anyway, like on the C7 RS6).

    Any info would really help guys, so any responses sould be hugely appreciated.

    Many thanks,

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  3. ShaunS3

    ShaunS3 Yorkshire & Humber Rep. Regional Rep VCDS Map User

    Most of the R&D for the S4 B6 is done over in America so that's where the info is.

    There's a tuning company called JHM / JH Motorsports who do all things S4 V8... they use a company called Fast Intentions for bespoke exhaust fabrication of their branded system.

    From what i know, that custom system uses 2x 200 cell sports cats which should be safe for UK mot regulations.

    I will be going down a similar route to the fast intentions setup by having it custom made here in the UK.

    I am already running the miltek downpipes which removes the oem impossible to get to cats and as an easier alternative, 2x 200 cell cats will be fitted at the bottom like most oe cat locations.... saves hassle for mot and if they ever need replacing, easy access.

    Hope that helps?

    Sent from my SM-G920F using Tapatalk
  4. ven

    ven Active Member

    From what i have read up on, 100 cell is a bit hit/miss for passing. 200 cell would be a better choice as mentioned. I too am looking into my options, mine being an auto/tip makes it more tricky(expensive to). Or simply do away with the pre cats.

    i dont know why you want raspy, you need deep growl. Raspy is for scooters! . I think the none resonated miltek is louder than you think. It does sound a little underwhelming at times, but outside the car is a different matter. When mine was in for MOT a few week back, you could hear it from 200yrds down the road. Its just well insulated in the cabin. But there are times when i want a little louder. But i also dont want MOT head aches to.

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