Downpipes, to cat or not???

[Shadow2]

Hi all, new member/owner here, '13 S6. Anyway I just picked this sled up a week ago, and am already planning upgrades. Im looking at a stage 2 ecu tune and downpipes, question is should I go with or without cats? Whats the power difference between the 2 and can the CEL be coded away in the tune? Car is daily driven with the occasional trip to the drag strip, and at least for the meantime will retain the stock cat back exhaust system. Not too worried about noise either.

[S4Per]

I ran no cats with my RS4 for a year. Stinks like hell, is terrible for this Earth we live on, and not sure if there's data that shows significant perf improvement over high performance cats. I finally went with the latter and couldn't have been happier.

[highPSI-S4]

I think every car I have owned at some point was catless. I grew up around hit he drag strip so many folks were catless for the fact of exhaust sound and performance with race gas.

Also race gas is bad for cats.





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[Shadow2]

Didn't even think about the race gas angle, thats something I was definitely wanting to try out. So AMS or the Russian eBay pipes? Still concerned about emissions though here in NoVa...

[low-profile]

Leaded race gas is bad for cats...and your O2 sensors for that matter.
Unleaded race gas is fine for either.
I would go with catted downpipes if you are concerned about emissions.


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[drivenagain]

Leaded race gas is bad for cats...and your O2 sensors for that matter.
Unleaded race gas is fine for either.
I would go with catted downpipes if you are concerned about emissions.


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^^This^^

[wwhan]

The AMS catted down pipes will work with stock tune, Apr tune or Epl tune.

The Apr down pipes work best with the Apr tune, but not with stock tune or Epl tune (in which case J extensions on the O2 sensor would be needed).

[WhiteDiamond]

Leaded race gas is bad for cats...and your O2 sensors for that matter.
Unleaded race gas is fine for either.
I would go with catted downpipes if you are concerned about emissions.


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Who cars about leaded race gas being bad for cats.......Try running some through injectors. That will end well.

Modern high flow cats are excellent and there really isn't a reason to not go the cat'd route. A few passes down the track are not a reason to go cat-less.
Personally, the AMS or Russian made pipes with the GESI UHO cats is the way to go. I have seen plenty of dyno tests on other forums, not Audi forums, to know there is no HP/TQ to be had going cat-less vs a high flow cat.