Fairfax 4.0T

I'm interested in the ability to make the exhaust of my S6 louder in dynamic mode, and return it to stock volume in comfort mode. My hope was find an aftermarket muffler that had movable flaps, like the stock exhaust system, but was louder when the flaps were open.

First, I wanted to learn the control signals on the wires going to the electric motor that controls the exhaust flaps. This is explained in some detail in the Audi 4.0T <a href="http://dl.dropboxusercontent.com/u/74111401/4.0%20engine%20self%20study.pdf">Self Study Guide.</a> Note that the link to the document appears to from one the Audiworld members, thanks!

Basically, the self study manual explains on pages 77-79 that:

Activation of the exhaust flaps is managed through the ECM. The commands “Open actuator” or “Close actuator” are issued using a PWM [Pulse Width Modulated] signal. Diagnosis
of the electric actuator takes place over the same line, also using a PWM signal.

Thus, it's not a simple on/off signal, but a more complex signal that could not be applied to a generic exhaust flap mechanism. I though that this would be OK, because I could still take the control motor off the existing exhaust and put it on an aftermarket exhaust.

Here's a picture from the 4.0 Self Study Guide of the motor that changes the flap position:

<img src="https://lh5.googleusercontent.com/-ERAkXSHJ7Es/UZl4hlHtzrI/AAAAAAAACIw/5ws-sO6857Q/s512/Exhaust%2520Flap%2520Motor.jpg">

According to the self study guide:

Exhaust flap switching is map dependent. The following factors are considered by the ECM when calculating the map:

- Engine load
- Engine speed
- Gear selected
- Vehicle speed

Next I wanted to figure out when the exhaust flaps are opened and closed. I connected my Ross-Tech Vag-Com to the OBD port, went to the engine controller and monitored some parameters as I drove around, including the car speed, flap position, accelerator pedal position, and whether the engine was in 4 cylinder mode. [Note that the the current version 11.XX of the Vag-Com software doesn't really work with the 4.0T, and I had to use the 12.XX beta to read/monitor/log the engine parameters.]

Here is what I found:

4 Cylinder Mode - Exhaust flaps are always closed when the engine is running in the 4 cylinder mode, regardless of whether the exhaust is set to comfort or dynamic.

Parked/Low Speed - Exhaust flaps are always open when the car is stopped or the car is running slow, regardless of whether the exhaust setting is comfort or dynamic.

Dynamic Mode - While I did not do complete testing in every possible situation, it seems like the exhaust flaps are always open when in the dynamic mode, unless the engine is in the 4 cylinder mode.

Comfort Mode - The exhaust flaps move to the closed position at around 65 to 77 Km/hour. When the flaps are closed and the car is coasting to a stop, the flaps open around 25 Km/hour. [Vag-Com displays the units in Km/hour, not mph]

- - - - - -
Conclusion: Even if you could mount the existing S6 Exhaust flap control motors to aftermarket mufflers, you can't get a loud exhaust and set it to a quiet mode using the MMI setting. The best you can do is have the muffler become quiet in 4 cylinder mode, and also in Comfort mode when the speed of the car exceeds about 70 to 75 Km/hour.

Oh well, I'm not going to pursue constructing an exhaust system myself any further, but it was interesting figuring out how the exhaust flap works, and what causes it to change positions.

Jim

RobC

Thanks for taking the time to post the info as well take the VAG data to see when the flap opens and closes.

I'm a little surprised that the signal to control the flap is PWM. It's not like the flap speed needs to be controlled, nor would I expect the flap to be partially open. Therefore a high/low signal seems like it would do the job.

Berto

Hi!
I was looking for info about exhaust flap of other Audi, and saw this post, nice info
what vag-com channels showed the flap position? in my car isn't documented.

TIA

Fairfax 4.0T

You probably need to update to the Ross Tech Vag-Com VCDS Beta software. I can't remember what, but some the non-beta software could not read all of the controllers/parameters.

To determine if the exhaust flap was open, I logged:
Exhaust flap bank 1-Channel 825

I also logged:
Group 554 - Field 0
Time in partial engine operation

to determine if the engine was in 4 cylinder mode.

S6Express

Jim, this was an outstanding post and very informative (at least for me) since I was wondering what made the valves open and close.

I attempted to have new, larger ovals welded on the other day. The ones I bought were quite deep and would have required removal of the valves. I wasn't sure how they worked, so I didn't have the tips installed.

I guess I can unplug them in the open position so that they don't shut and see what difference that makes in terms of sound. Has anyone attempted this with the stock exhaust. I know that the AWE exhaust comes with plugs for the cables and there will be an error code about the valves. But I wonder how different my car will sound with the stock exhaust and the valves removed or in the open position.

Martin89

SportLine is there any chance you can post a video of the sound of your exhaust?

I have removed my front silencers and mid-box with a h-pipe. It sounds awesome but I wonder if modding the rear mufflers will improve the sound greatly

Martin89

Here is my exhaust could not take a video while driving it so here is a stationary one recorded it with my LG G3

Martin89

I will try to find someone to film it for me or maybe setup the camera on some strip of road. The silencer mod which I'm thinking of doing, will it have any drone which you find annoying?

Sport Line

No drone , and as a matter of fact I been surprised to find out that even driving with no mufflers for almost a week there where really no drone either! One simpler mod you can do it's to do a little V shaped cut on each muffler , like a inch long so you can bend that and pull the fiberglass out from the muffler .After you can just straighten that back and have it weld at a shop when you have the chance. Use one of those Dremel EZ Lock discs , you can have it attached to a regular drill , using this will do a very thin cut on the muffler (make shore to stick a patch of a aluminum scotch tape until you have it weld). After doing this there is really not much difference comparing with the bypass I did , you should be happy enough

P.S I just had the x-pipe removed and the front silencers as well! Straight pipes all the way until the mufflers!

Martin89

Thanks Sport Line, great pics and I think I will try and do a bit of DIY myself as I'm sure it will sound better without the fibreglass in the mufflers