Peron downpipes

[Rsben]

As above anyone running these, or know the quality of fitment

Ben

https://peron-automotive.co.uk/products ... rs6-c6-v10

[Stiggles]

They look like a great bit of kit, I'm not sure what any other downpipes look like but I'll be getting a set soon

These might be a contender, and they actually look like the ones I saw fitted to a car on the lift at MRC a few months back

[cammmy]

These cars have 4 cats? Two primary and two secondary? I've read that you can remove the secondaries and still pass MOT but is the same true if you remove the primaries and leave the secondaries in?

There's also these but they're seriously expensive:

https://www.kwe-racing.de/Audi/Audi-S6- ... anguage=en

You can tell by the shape of the cats that they're well designed though.

[welwynnick]

Did you mean to link these downpipes instead? These are the expensive ones that do have cats.

https://www.kwe-racing.de/Audi/Audi-S6- ... ::850.html

Nick

[Per_S]

The KWE downpipes are known not to fit. You can expect to spend quite some time adapting them to your car.

[cammmy]

Did you mean to link these downpipes instead? These are the expensive ones that do have cats.

https://www.kwe-racing.de/Audi/Audi-S6- ... ::850.html

Nick

Thanks, most likely. The site is blocked at work so I copied it from the google results.

[cammmy]

The KWE downpipes are known not to fit. You can expect to spend quite some time adapting them to your car.

Wow. Given the cost, you would expect them to be bolt on.

[welwynnick]

These cars have 4 cats? Two primary and two secondary? I've read that you can remove the secondaries and still pass MOT but is the same true if you remove the primaries and leave the secondaries in?

Best not to think in terms of primary and secondary cats, because the cats do different jobs.

The front cats are reduction catalytic convertors, because they use the CO in the exhaust to reduce the oxides of nitrogen to nitrogen and carbon dioxide.

The rear cats are oxidation catalytic convertors, because they use the O2 in the exhaust to oxide the CO and the unburnt hydrocarbons to CO2 and water.

Both cats are needed for type approval, but only the oxidation cats are essential for MOT tests because nitrogen oxides aren't tested.

That's why people often say you can get away with "primary" cat delete.

In many cars the two cats are integrated into one unit. You can spot those by the lambda sensor sticking out of the middle of the cat.

Nick

[Rsben]

So basically I can delete the primary cats in the downpipes and keep the secondary cats which will be ok for mot testing

Ben

[cammmy]

Thanks, that's great info.

[Toady1]

Not so true, I had primary cats only in my stg2 MRC car, secondary cats removed. It still passed MOT emission testing. But removing the primary cats with bigger DP's will definitely fail!

[IanH755]

That's why people often say you can get away with "primary" cat delete.

Hi Nick, just to clear up the confusion here with what owners are describing as primary and Secondary cats -

Primary Cat - Quite small and situated at the top of the downpipes right next to the turbo (within cm's of the turbine). Very rarely removed, normally just get de-cat downpipes instead and it WILL fail an MOT with these removed.

Secondary Cat - Much bigger and looks more like a "traditional" cat and is fitted right at the bottom of the downpipe where the exhaust bolts on. These are what people remove all the time on C6 RS6 and it WILL still pass the MOT with these removed.



That is how owners usually describe which Cat they are talking about and why you'll here "secondary Cat delete" mentioned so much. Hope that clears this up.

[welwynnick]

Hi Ian,
Now I'm really confused. I researched this a few years ago, and there are some facts of which of I'm certain, and some less so.
The certain ones first. For over 30 years, all new European and American petrol cars have used three way catalytic convertors.
3 way means there are 3 pollutant types that are converted - carbon monoxide CO, unburnt hydrocarbons HC and various oxides of nitrogen NOx.
The cat is actually two cats - a reducing cat and an oxidizing cat, though they're usually integrated into one unit.
A few fast cars like RS4, RS5, RS6 & some M3 have two separate units per bank.
The reducing cat reduces N0x to N2 and CO2, and the oxidizing cat oxidizes CO and HC to CO2 and H20.
The ECU oscillates the mixture strength either side of stochiometric in order to release both CO for the reducer to use, and O2 for the oxidizer to use.
That's straightforward - now the uncertain bit.
To the best of my knowledge, the exhaust goes into the reducing cat first, and then the oxidizing cat.
It's not generally well known, even by tuners, but try doing a google picture search for "oxidizing catalytic convertor".
You'll see some pictures that show integrated cats where the exhaust flows into the reducing cat first, and then into the oxidizing cat.
Maybe it could be done the other way round, but reducing first makes sense.
The reducer releases oxygen which can be used by the oxidizer, but the oxidizer doesn't release CO for the reducer to use (it would oxidize it instead).
Therefore I think it's reducer first, oxidizer second, and I've never found any exceptions to that. The reducer is usually smaller than the oxidizer.
Therefore while I'm not CERTAIN, I believe the RS6 front cats are reducers, and the big rear ones are oxidizers.
The MoT test measures CO and HC, but not NOx, therefore the reducing cat can be removed and still allow the car to pass the MoT, but NOx emissions will be high.
By the way, the picture above shows the KWE catalyst downpipes, and I think the bends at the front are just that - bends, not primary cats. You can tell because there are no lambda sensor bosses in front of the bends, and the primary lambda sensor is ALWAYS in front the cat, so it can measure the actual oxygen content in the exhaust gas.

Never mind all that, how's YOUR car doing?

Nick

[IanH755]

That's being a bit too literal on the pic there Nick, it was just a generic C6 image I found in Google that I used to show which cats are located in which area of the OEM exhaust, not this specific decatted downpipes KWE one.

As for mine, I'm not back in the UK til April. Currently the GB should be in/out soon and all the DRC refresh parts have finally arrived after a 6 month delay in getting parts from Audi Germany. There's also a few TLC fixes along with general housekeeping like new discs, oil, fluids etc being done too.

[c3nturi0n]

That's being a bit too literal on the pic there Nick, it was just a generic C6 image I found in Google that I used to show which cats are located in which area of the OEM exhaust, not this specific decatted downpipes KWE one.

As for mine, I'm not back in the UK til April. Currently the GB should be in/out soon and all the DRC refresh parts have finally arrived after a 6 month delay in getting parts from Audi Germany. There's also a few TLC fixes along with general housekeeping like new discs, oil, fluids etc being done too.

hey Ian,

and thx for your input... what do you consider by DRC refresh?

ps. i had my DRC system flushed last year as part or rear shock replacement.


Cheers, D