Verybumpy

Assuming I'm in Auto, if I accelerate to the 2800 rpm range and beyond, my exhaust gets noticeably loud. If I keep accelerating but on let it dip down to say 2300 rpm on the next upshift, the exhaust awkwardly gets quiet instantly. Then it'll go loud a second later if I accelerate a bit more again. It's constantly switching back and forth between loud and quiet.

Is this normal for the V8 4.0 TFSI or any Audi engine?

MP4.2+6.0

Covered (I think) in the Audi technical documentation for a given motor and engine, and sometimes with a new body intro or similar substantial change.

Short version is it is a combination of RPM and acceleration IIRC, plus driver adjustability in MMI. Thus, mechanically flaps are opening in the exhaust (back at the rear cans if you look). Those are common place these days if you look at other vehicles and can see the exhaust, whether 2.0T's or BMW counterparts or whatever. Simplified, closed for gentle, and open for aggressive or when it just plain needs it for performance (or fuel economy). On top of that, you have the electronics. Here I don't know what an A8 4.0T has specifically, but on an S8 there is what (at least in the VW world) is called the Soundaktor--piped in fake noise through a speaker. On at least VW's it also introduces some (intended) vibration into the sheet metal. On the S8, you can choose in the settings whether to emphasize it or not. Before MMI tuning of it of it, you could disable it or modify the intensity with VCDS, or outright pull the plug on the speaker like I did recently on my last gen Golf R. Further, and again speaking to the S8, there is also active noise cancellation, at least post facelift. That uses the stereo to introduce 180 degree offset sound waves to cancel unwelcome sounds, including from the cylinder deactivation function. If you see little round microphones near the roof grab handles around the car, you have that too.

You don't say what year your 4.0T is. Speaking again to what I know more--the S8--additional sound dampening was introduced with the facelift. Some further sound insulation and a heavier trunk floor. Some A8's have the trunk floor one--I think the ones with the Barcalounger option or something else as an upgrade to the rear seating. Acoustic (double pane) glass makes a difference too, depending on how yours is equipped.

Verybumpy

Hmm...so no definitive parameters.

I wonder if the OBD Eleven has the ability to turn off or better control when this exhaust valve operates?

96gs917

I have had my 2018 SQ5 Prestige for 2 months, and today after washing it, I noticed while at idle the exhaust was only exiting the passenger side.
I stick my hand under the driver side, and nothing. The car was warm. I have the MMI set to individual, with the exhaust set to dynamic.

Is this normal?

MP4.2+6.0

Yes, there may be parameters, but you would have to search the definitive technical materials as I mentioned. Not the sort of info people walk around with in their heads.

Basically, no on the parameter mods. Putting aside whether OBDEleven will have all the functionality of VCDS for a given task, these have never been defeatable or modifiable with VCDS AFAIK. On the earliest ones, you could pull the vacuum lines that drove the valves in order to leave them open all the time and they were spring loaded that way. Later things were changed and the spring loading was toward closed so if you wanted them open all the time you had to use baling or similar wire to do it. By D4 they are now electrically driven, so even the old vacuum or baling wire permanently open (or closed?) mechanical mods are out the window. But, it's an odd situation in that the early threads about this (they started on the D3 W12) were about increasing the sound, while here it is to decrease. There are technical drivers to these too--how they affect performance, fuel economy and emissions warm up. Further complicated by general shift from normally aspirated to turbo/blown. On N/A you typically wanted back pressure at lower RPM's to increase torque, so having them closed was better in that mode, even if the "kids" wanted the sound. Not sure if blown motors really care about that. But for smog, you want the cats to heat as fast as possible. I think that means closed. Also on hybrids you want to keep that exhaust hot for normal run mode, which also means closed--I have them on the 2.0T Q5 hybrid and recall from the materials that is one of the parameters.

MP4.2+6.0

See other reply. First, yes it may be normal in general. At idle I would expect them closed. Near idle and up to about 3K same answer if like on a normally aspirated it provides more back pressure which maybe counterintuitively increases low end torque at least on an N.A. motor. Also depends on how "warm" warm really is. After driving a while, agreed. If still near start up but only to point where heater has kicked in, maybe not enough.

Yes, by the way, the newer systems may have cheaped out more and are cutting out just one whole side. When first implemented on the D3 W12, it also had quad exhaust exits from the final cans like an "S' model. They were buried by some bumper trim though so just looked like dual trapezoidal outlets. On that first design, each side was switched so exhaust still flowed through a somewhat smaller exit port from the cans on each side. On my Gen 1 Q5 Hybrid, it only has duals (not quads) anyway, but it cuts off a whole side when cold and you can see it sometimes.

MP4.2+6.0

FWIW, below are the 4.0T descriptions on this system. Does not get into the parameters still.

mutant9

Has anyone found a way to control the exhaust valve on the D4? Would be great to have it defaulted to open when the car is in Dynamic mode.

spdemon91

I believe you can adjust this setting with VCDS. Also, I have seen someone zip-tie the valves to keep them open but that may have been on a D3.

spdemon91

Here's a video on how to disable via VCDS on an S3... Not sure if this would work on an A8/S8 and I don't have a VCDS yet to try it. Anybody else with experience on this?