Exhaust system

[mbagge01]

Does anyone know what the diameter of the stock RS6 C5 Exhaust is. I have the SE version. I am considering upgrading to an aftermarket exhaust if the pipes are bigger but i know I will not see much of a performance exhaust unless I also get an upgraded downpipe.

[lswing]

Cleared downpipes will make big difference, you've got two sets of cats in there. Increasing exhaust diameter in general will not result in much. Get those cats out of there so she can breath! Don't you have emissions there though?

I'm assuming you're tuned...

[mbagge01]

Yes we have emissions. If I get a downpipe with high flow cats and use 02 eliminators or code out egt, could I pass emissions that way. Here, there only check obd2 codes for emissions testing.

Cleared downpipes will make big difference, you've got two sets of cats in there. Increasing exhaust diameter in general will not result in much. Get those cats out of there so she can breath! Don't you have emissions there though?

I'm assuming you're tuned...

[mbagge01]

I mean code out secondary 02, not egt

[audiprotn]

By removing secondary cats ( bigger ones) you should not have any cel.
If you remove primary, you would need to code it out, usually tunes already include this option in their software.

[ianh755]

Stock Audi exhaust is 76mm (2.5in). Milltek etc are usually around 2.75in but as lswing mentioned the stock pipe diameter isn't a restriction but the catalytic converters in the downpipe are. If you can remove just the pre-cats (or secondary cats if you call them that) it'll help reduce EGT's, decrease spool up time/revs and sound better.

I think tuning companies sometimes forget that each individual 2.5in pipe is only dealing with 4 cylinders putting out around 225 to 275 flywheel hp depending on average tune (stock to 550hp) so the exhaust diameter is fine which is why I'm surprised at companies selling 3in downpipes which people are putting on a mild tune for example. I mean a 3in exhaust on 4 cylinders is only really needed for 500hp+ meaning a 1000hp RS6 which would be amazing! Yes the turbos will like the slight reduction in back pressure but just removing the cats will have a very similar effect and the actual HP increase from a wider exhaust will be fairly un-noticeable (say 20hp) when you've already got 450+hp anyway.

Anyway, all of that is only in my very limited opinion . I'm not a mechanic but I've owned and tuned a few 400hp+ turbo cars and have seen the results on those cars.

[Beardown1]

I gutted my pre-cats and moved the secondary O2 sensors behind the main cats. Never had a code. The combination of the gutted pre-cats and JB weld sealed IC's resulted in a huge kick in the pants improvement!