Exhaust options.

[boff]

Just drop it into S as soon as you start it. then you don;t need to wreck any clothes.

But then it is not open all the time.

Really - I thought S was flaps open?

[MikeFish]

Most cars still close the flaps at certain points even when in 'open' mode.

I think this is to pass noise regulations so open at idle then they close them at lower revs then reopen once it starts really revving about 3-4k rpm. I assume the C7 is the same or similar.

Incidentally, it turns out that the disconnection of the exhaust valves creates alarms. No indication on the dash but they are picked up on a scan as I found out at MRC today.

[boff]

Probably one to avoid for now then.

[MikeFish]

It doesn't create any issues Boff, other than when you plug a laptop in it says there are error codes. Car sounds so much better now with my modded exhaust and flaps disconnected. I may even connect the valves back again. I'll see how it is after a few cold starts.
I must say, when it was on the dyno at MRC today it shook the place, i was surprised how loud it was. Then Doug came out and asked me why it was so quiet. I think he is used to all the non res millteks and anything less sounds too quiet.

[boff]

What you mean Doug walked out and said?

Mike why did you waste your money on those exhaust mods, when really you should have come here and paid me millions of pounds for a cheap milltek?

Muhaha muhahhaaaaaaaaaa

[MikeFish]

LOL, he did say if I want any gains I will need an aftermarket exhaust like the milltek.

[boff]

Chuckle - Secretly he was in his office and thought - what the <beep> is that? To save face he came down and gave you some BS about the Milltek and Power Gains....... Audi do not put restrictive exhausts on 600BHp cars.

Therefore it is total BS

and secretly he was impressed which is probably why he came down

[MikeFish]

No there is some truth to it. Max power after remap with OEM exhaust / Milltek cat back is about 50bhp lower than with a Milltek turbo back system i.e. sports cats. So the cat back bit is OK, but the OEM cat seems quite restrictive. Not sure if just removing any pre-cats would make it the same like it did with the B7 though.

[boff]

Hmmm - fair enough Mike. Do you think the tuners hold back on the map for people who have bought the exhaust?

[vestax32]

Mike, so have you now had secondary cats and central resonators removed? What's it like? Any drone at motorway speeds? Is it overly loud, or is it acceptable for daily use?

[MikeFish]

I had the centre resonator removed as well as the 2 boxes in front whatever they are.
It sounds great now. I have the valves disconnected and didn't notice any drone at all. I did nearly 200 miles today but it was all A and B roads, no motorways so there was not much cruising at 90ish bit I did get some speed and didn't notice any. In fact if I shifted into D instead of S (but valves still open) you could barely hear it. Not too loud but it can now be heard inside the car a little bit and much louder pops.

[Leo-RS]

Yes, the tuners have to hold back due to the science behind gas flow. Everything has to fall in line with the EGT limits of the turbo and engine.

EGT's (Exhaust Gas Temps) are lower with a less restrictive exit, with a cat in place, there's a restriction, gas flow slows (lag) and temperature increases. As temperature increases, the ECU protects the engine hardware by pulling out boost and timing and at the same time richens the fuel mixture (lambda/AFR) in order to cool down the EGT's. Runaway EGT would be bad news hence the ECU safe guards in place.

With the exhaust opened up, tuners can better control this EGT limit, add in more boost and timing, increase the spool time and as a result increase torque and power.

The RS6 is a completely different animal with a turbo back exhaust, the sound and response is unreal. I know these are just words written on a forum but an exhaust really does transform the car. Both the sports and standard exhausts are very tame, I was disappointed with the noise the first time I took one for a test drive. Now I can't get enough of it, the pops and crackles are very addictive.

[Surrey Sam]

Not sure if just removing any pre-cats would make it the same like it did with the B7 though.

Thought it was established there were some collectors on the standard system rather than pre cats.

Or have I just sunk too many beverages for this time of the evening

[Andy_W]

How much difference can there be to say a Milltek non res and the OEM sports system with the centre sections taken out from a power / mapping gain point of view? I can't believe there would be that much difference specially with the valves open.

I'm really impressed with the sound of mine now (like Mikes) and glad I gave this a go before spending 1000s on a full aftermarket system. I would be interested to have a ride in one with a Milltek or Akra though to see if there is much difference in sound.

It's loud on boost / accelerating but very refined still crusing. Even cold starts are quite tame compared to the Larini R8 I had. That was crazy!

[MikeFish]

Not sure if just removing any pre-cats would make it the same like it did with the B7 though.

Thought it was established there were some collectors on the standard system rather than pre cats.

Or have I just sunk too many beverages for this time of the evening

You may be right Sam. I tried to find a detsiled explanation of the C7 exhaust system but couldn't find one. I have read various descriptions thoug, some saying precats, others saying primary and secondary cats and now collectors which I'm not sure I fully understand.