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What activates "active exhaust"?

18K views 42 replies 22 participants last post by  JTB488 
#1 ·
Went to the track last night. Used the "custom" page for setting up for the strip. Trans on "track" setting, suspension on "street", paddle shift off, traction on "sport". Asked my friends so how does it sound going down the strip. All said quite. Wouldn't the active exhaust be open then?
 
#3 ·
I don't know about what those specific settings would sound like, but I do know that when I put my SRT in Track Mode, there is a noticeable difference in the exhaust note -- it is much louder than the other settings. In addition the steering is much tighter, the acceleration feels quicker, and the ride is much stiffer. At least to my ears. Some people have said there is no sound difference in any of the settings. Others have said that the flaps in the exhaust are open all the time in Track Mode, while others have said that is not true. Like "Fast", everyone has a different opinion as to what constitutes "Loud". I would like to see a complete rundown from an engineer that knows, exactly what each of the settings do, besides the obvious like stiffer ride and tighter steering. BTW, I've read other posts on other sites that claim the Scats and SRTs are quite at the track on their returns -- mostly because they are not being stomped on. I haven't been to the track this year so I can't say.
 
#4 ·
I'm not sure of the specifics of when they open. The only thing I know for sure is that if you have an A8, they'll be closed when MDS (4 cyl) activates. And I know they'll be open at WOT regardless of what mode you are in.

When you say you asked how loud it was when going down the "strip"... if you mean dragstrip, just about any street car is going to sound quiet on the strip after hearing track cars with open exhausts. It's a mental calibration thing. Even if a drag car only runs every 10th time, they are so loud that they raise your threshold when watching races. On the street, I'm convinced it's the loudest production car made (at WOT or even heavy throttle). I've never had a car that sounded this good. I've had Corvettes with Magnaflow and Corsa exhausts and neither sounded this good/loud. In some situations, it's almost too loud because I find there are times that I'd like to step on it a bit but I hold back because I don't want to attract attention.

Mike
 
#6 ·
I know that my car doesn't sound any different at idle in any of the different modes.
Maybe they stay closed at lower RPM's or loading for better back pressure and scavenging.
 
#7 ·
I know that my car doesn't sound any different at idle in any of the different modes.
I thought they stayed open at idle and then close as you start to pull away. Even so, they still allow exhaust thru even when closed.


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#8 ·
The active exhaust is always open in sport mode, or opens automatically in normal mode when you floor it. You can't tell when the butterfly valve is open at idle, it sounds quiet either way. I guess the muffler is doing it's job there. But if you put it in sport mode and give it a little throttle tap, you should be able to hear the difference. The valve also stays open on startup for about 2 minutes. That's what gives it a nice bark when you start it up.
 
#10 ·
Being that this is the SRT forum, I assume we're talking about SRT's. On an SRT, I don't think the valves stay open until you hit Track mode. In Sport mode on an A8 SRT, it still goes into MDS (4 cyl) mode and as I understand it, the valves are always closed when MDS activates. In track mode, MDS is never active so I believe the valves are always open in Track mode. On a Scat Pack, the valves should be open all the time in Sport mode (and MDS deactivated) because Sport is the highest setting on a Scat.

Mike
 
#11 · (Edited)
On my 15 it will still go into 4 cycl. mode in Sport as well.
My exhaust opens for about 30 seconds if the eng is cold and it will open at about half throttle - I'm certain I don't have to go anywhere close to WOT. Actually surprised me one time when I went to pass someone on the freeway. All was quiet just cruising along and then give it a little too much gas to pass someone and it goes into Cookie-Monster mode.
I will try blipping the throttle in all the modes to see if it's louder but at idle it is exactly the same in every mode.
 
#12 ·
I'm a little late to this thread, but can anyone VERIFY that the valves stay open in "all modes above default" or even in Sport mode on the SP? I"m reasonably sure that they open with less throttle in all modes except track, but they are most definitely not all the way open. Start you car, let it warm up all of the way and turn sport on and off... the car will sound the same. At least it is in the SP.

Plenty of throttle opens them up all the way in default on my SP, and less throttle opens them in Sport –But they don't seem to be open all of the time. I want to be able to open them all the way at will, but it looks like there isn't a product for our cars that does that just yet.
 
#14 ·
I'm sure I've read about 90% of threads covering the active exhaust question and I have not seen a definitive answer from anyone. Only...... hearsay

Most logical answer I've seen is that A8 owners are hearing a difference because of the transmission shift points being altered, not because of the valve opening or closing.
 
#22 · (Edited)
You don't think much of our judgement I guess.
Suffice to say you are wrong. The sound of the valves being open are distinctive and are more associated with throttle position and not even eng loading so much. It's not because of something the trans is doing.
Also, we have idled the car in neutral and switched between modes (Track, Sport, Default - there's no "street") and there is no change in tone or volume. We've done this with several people and even backed it up against a wall and it's clear that nothing changes.
A more likely scenario is that manual trans cars have a different algorithm for their operation and that's why people have different perceptions - not because A8 owners don't know what we're listening to.
 
#15 ·
I have an M6. Sport mode, they're open all the time. You don't need to floor it.
Just drive next to a wall in both modes and you'll hear the difference.
 
#16 ·
This is not definitive proof that they are open all of the time. It's pretty obvious at idle that they aren't open all the time (just start the car and immediately put it in sport mode, you'll hear them close). What sport mode does do, it make them open at lower throttle positions. This is part of the "engine" setting for Sport mode.
 
#18 ·
So, basically, no one really has any conclusive knowledge or understanding of how they work. Interesting! I can personally disprove half of the ideas in this thread from basic actual experience (SRT, A8). Maybe the SRT guys can fill us in, didn't they used to come onto the forums sometimes?

The only other way would be to monitor it, which is hard, but you could piggy back on the wires and put in a small light or something to show when its opening or closing.

Does anyone know how fast it opens or closes? As it doesn't need to make a complete seal I guess it could be quick. Other systems I've seen in the past can take 2-3 seconds to go from open to closed or vice versa.

Cheers
 
#21 ·
If its throttle controlled, makes more sense than in track and sport, the valves open sooner. The throttle is much more sensitive... I don't think they physically stay open just by turning on either mode. At idle there's no noise difference, if any of these modes triggered the valve to stay open, it would be really obvious. To me, the car is still pretty quiet in all modes when cruising around. The only thing I do notice is that there's alot more crackling and popping when letting off the throttle in track.
 
#25 ·
Cars at a drag strip can be ridiculously loud to the point that it literally hurts your ears, and everything is relative. In my opinion the SRT exhaust sounds pretty good, but not great for being stock. I don't care much about sound anyway. I'm more worried about bite than I am bark.
 
#29 ·
Yup, those that have tried it report back that it throws a CEL anywhere from same day to a few days later.

I pulled mine anyway this morning... yes, this is exactly how I want my car to sound all of the time. Dangit!
 
#37 ·
There must be a difference with auto vs stick, there is a very clear difference around town at a steady speed and RPMs around 2000 when I press sport vs street. As soon as I hit the button it gets louder and accelerates slightly due to the modified throttle curve.

On the freeway with the cruise set there is zero difference in sound and there's no acceleration when sport is turned on. I wouldn't have expected any acceleration with cruise set anyway since it changes the pedal sensitivity, but no change in exhaust tone tells me that sport doesn't open the valves more just because sport is turned on.
 
#38 ·
I know for sure there's a huge difference in the "tip in" or "trim of the accelerator between the two modes on my car.
1/4 throttle with default mode gets you a nice hard pull from stop but the same in "track" snaps your head back and cooks the tires.
The difference is dramatic.
 
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