factory 04 exhaust

[gsxtrip]

might just be a stupid question, but I am in the process of waxing my car when I get to the bumper I look in the exaust opening and see that after the muffler there are two pipes coming into one. One of the pipes looks like it has a butterfly valve that has a linkage coming out of it. I know the RS4 has this on the dual pipes that I think is controlled through the sport mode button. What is mine for, and what controls it to open and close?

[ChronicTeutonic]

The S4 flaps are controlled by engine vacuum. If you get under the bumper you'll see a tube that runs from the flap control to a vacuum line on the bumper. The flaps are there to control the drone under 2000 rpms buy circulating the exhaust gas through the rear muffler. When you romp on it the flaps will open and exhaust will be straight through improving flow.

The S button in the RS4 essentially overrides this feature.

Incidentally this is why aftermarkets systems have the drone issue...

[gsxtrip]

Great info, thanks for your help.

[RAudi Driver]

I actually think that the flap is there to make the car sound meaner at idle and quieter at highway speed.

At anything below 1700 rpm, both tubes are open allowing exhaust gases to exit. When the motor revs above 1700 rpm's, the flap closes down one of the exit pipes to keep the car quieter.

Hope this helps.

[ChronicTeutonic]

From the Audi Training Manual 921603 available on the Bentley site if you subscribe:

Audi RS4 Exhaust Flap Control

A further difference is the layout; one exhaust flap is
located downstream of each of the rear silencers. The
exhaust flaps are fitted to give the engine a sporty sound.
Low-frequency droning noise at low engine RPM is
prevented. At high engine RPM and high exhaust gas flow
rates, flow noise and exhaust back pressure are reduced
by opening the additional cross-section.
The exhaust gas flaps are closed at idle, low engine load
and at low engine RPM.

Function
The exhaust flaps are switched by a vacuum actuator.
Both vacuum units are switched by an electrically
activated solenoid valve. The exhaust flaps are switched
according to a characteristic map.
The factors of engine load, engine RPM, gear selected
and the shift signal from the Sport button are used to
plot the characteristic map.
For example, the exhaust flaps are opened at idle when
the Sport button is pressed.

[CHECKERED]

C6 Z06 Corvettes and 2008+ C6 with factory upgrade exhaust have the same thing…but you can override it with an aftermarket switch, makes the car sound bad ass at low speed cruising

[NYCS4Avant]

Do a search for "exhaust flap mod" in the B6 forum. You'll come across a number of AZers (myself included) who have essentially "plugged the lines" with everything from golf tees to screws. Not sure if its actually done anything noise wise but hey, whats life without a little DIY modding?

[gsxtrip]

thanks guys this is all great stuff.

[gsxtrip]

C6 Z06 Corvettes and 2008+ C6 with factory upgrade exhaust have the same thing…but you can override it with an aftermarket switch, makes the car sound bad ass at low speed cruising

I had a new vette in the shop a couple of weeks ago that had the exhaust mod that was controlled by a wireless fob, amazing how much it changed the sound

[fitzS4]

i disconected my flappers and under hard throttle you get a raspy sound...