2013 S8 Exhaust Analysis and Dissection
02-25-2017, 05:49 AM
#1
Audiworld Junior Member
Thread Starter
2013 S8 Exhaust Analysis and Dissection
I thought I would compile what I learned in my quest to liven up the sound of my S8. Sound, for me, is a critical part of the enjoyment of my cars. The relatively simple upgrade described below (hint: muffler delete) is exactly what I was looking for.
The Stock System
https://dl.dropboxusercontent.com/u/...2014.02.59.jpg
After the turbos, you have the close-coupled catalytic converters. Then under the car you have one cylindrical resonator per bank, followed by a large irregular shaped resonator toward the rear. Finally, you have the big mufflers with twin pipes out the back. The muffler is "active" in that an electrically controlled flap can close one of the tailpipes. More on this later.
The stock system is, I imagine, is quite free-flowing. I believe that the first resonators (or are they another set of catalytic converters?) are of a straight-through design, but I didn't take them off to verify this. The large second resonator is, however, strange. I thought it would consist of a long perforated pipe surrounded by sound deadening material. Instead, it is nothing more than an echo chamber (Helmholtz resonator) consisting of solid pipe with a slot cutout that is connected to a long empty dead-end chamber. BTW, just ahead of the resonator is a crossover passage. You will want to preserve this feature for sound and performance reasons.
The muffler is also quite interesting. There are two exhaust gas passages: one narrow one, and one larger one. The electric valve directs all gas through the skinny pipe until it opens at which point the gas can flow through both outlets. My valves were permanently stuck open because the electrical connectors were corroded. Even so, with the valve open the car was quiet. One thing about the stock muffler: I'm not thrilled about how the "large" passage is run right into the perforated plate toward the rear. Cutting it back even just a fraction of an inch would improve flow.
Pipe diameter after the cats is about 2.25" OD but expands to 2.5" after the first resonators. Decent sized for stock or moderately increased power levels.
My New System
Basically, I replaced the mufflers with straight pipe. The car now sounds amazing. At steady cruise, there is a little increase in noise. It might get a little annoying, however, if you were driving up a mountain and had to press the throttle more than with steady cruising. For me, I love it. If you want less noise, a simple straight-through muffler might be all you need.
Pics:
Stock muffler: If anybody wants to modify the stock muffler, go for it. The shell cuts open easily. All you would need to do to get more sound and better flow is cut away some of the perforated pipe, and puncture the perforated mesh a bit. An angle-grinder and/or reciprocating saw is all you need.
https://dl.dropboxusercontent.com/u/...10.45.19-1.jpg
https://dl.dropboxusercontent.com/u/...10.45.38-1.jpg
https://dl.dropboxusercontent.com/u/...10.59.22-1.jpg
https://dl.dropboxusercontent.com/u/...10.59.27-1.jpg
https://dl.dropboxusercontent.com/u/...10.59.38-1.jpg
https://dl.dropboxusercontent.com/u/...11.00.13-1.jpg
https://dl.dropboxusercontent.com/u/...11.00.51-1.jpg
Stock rear resonator: FYI-the slot that is cut into the exhaust pipe is toward the rear of the car.
https://dl.dropboxusercontent.com/u/...2014.02.59.jpg
https://dl.dropboxusercontent.com/u/...2014.13.56.jpg
https://dl.dropboxusercontent.com/u/...2014.14.19.jpg
https://dl.dropboxusercontent.com/u/...2014.14.41.jpg
Front resonators: Mine are brand new from the dealer. They replaced the original ones as part of a fix to deal with vibrations at 1000RPM and 3000RPM.
https://dl.dropboxusercontent.com/u/...2014.03.09.jpg
New Straight Pipes
https://dl.dropboxusercontent.com/u/...2015.20.06.jpg
Mike
The Stock System
https://dl.dropboxusercontent.com/u/...2014.02.59.jpg
After the turbos, you have the close-coupled catalytic converters. Then under the car you have one cylindrical resonator per bank, followed by a large irregular shaped resonator toward the rear. Finally, you have the big mufflers with twin pipes out the back. The muffler is "active" in that an electrically controlled flap can close one of the tailpipes. More on this later.
The stock system is, I imagine, is quite free-flowing. I believe that the first resonators (or are they another set of catalytic converters?) are of a straight-through design, but I didn't take them off to verify this. The large second resonator is, however, strange. I thought it would consist of a long perforated pipe surrounded by sound deadening material. Instead, it is nothing more than an echo chamber (Helmholtz resonator) consisting of solid pipe with a slot cutout that is connected to a long empty dead-end chamber. BTW, just ahead of the resonator is a crossover passage. You will want to preserve this feature for sound and performance reasons.
The muffler is also quite interesting. There are two exhaust gas passages: one narrow one, and one larger one. The electric valve directs all gas through the skinny pipe until it opens at which point the gas can flow through both outlets. My valves were permanently stuck open because the electrical connectors were corroded. Even so, with the valve open the car was quiet. One thing about the stock muffler: I'm not thrilled about how the "large" passage is run right into the perforated plate toward the rear. Cutting it back even just a fraction of an inch would improve flow.
Pipe diameter after the cats is about 2.25" OD but expands to 2.5" after the first resonators. Decent sized for stock or moderately increased power levels.
My New System
Basically, I replaced the mufflers with straight pipe. The car now sounds amazing. At steady cruise, there is a little increase in noise. It might get a little annoying, however, if you were driving up a mountain and had to press the throttle more than with steady cruising. For me, I love it. If you want less noise, a simple straight-through muffler might be all you need.
Pics:
Stock muffler: If anybody wants to modify the stock muffler, go for it. The shell cuts open easily. All you would need to do to get more sound and better flow is cut away some of the perforated pipe, and puncture the perforated mesh a bit. An angle-grinder and/or reciprocating saw is all you need.
https://dl.dropboxusercontent.com/u/...10.45.19-1.jpg
https://dl.dropboxusercontent.com/u/...10.45.38-1.jpg
https://dl.dropboxusercontent.com/u/...10.59.22-1.jpg
https://dl.dropboxusercontent.com/u/...10.59.27-1.jpg
https://dl.dropboxusercontent.com/u/...10.59.38-1.jpg
https://dl.dropboxusercontent.com/u/...11.00.13-1.jpg
https://dl.dropboxusercontent.com/u/...11.00.51-1.jpg
Stock rear resonator: FYI-the slot that is cut into the exhaust pipe is toward the rear of the car.
https://dl.dropboxusercontent.com/u/...2014.02.59.jpg
https://dl.dropboxusercontent.com/u/...2014.13.56.jpg
https://dl.dropboxusercontent.com/u/...2014.14.19.jpg
https://dl.dropboxusercontent.com/u/...2014.14.41.jpg
Front resonators: Mine are brand new from the dealer. They replaced the original ones as part of a fix to deal with vibrations at 1000RPM and 3000RPM.
https://dl.dropboxusercontent.com/u/...2014.03.09.jpg
New Straight Pipes
https://dl.dropboxusercontent.com/u/...2015.20.06.jpg
Mike
02-25-2017, 08:31 PM
#2
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do you have a pic of the mod of the straight pipes? Also did you take out the irregular shaped resonator in the center and just straight pipe that. I have been looking at doing the same the thing. Not a lot of options for the Audi, otherwise I was think about doing some electric cutouts, but was worried that if I straight pipe it that the electric valves would throw some error codes. Great write up!
02-26-2017, 08:54 AM
#4
AudiWorld Super User
Thanks for posting. As always, little deeper mechanical mod info exists on the D4 type boards and so really helps to see something here.
There have been a variety of posts on the C7 boards I have followed casually in last year or so--4.0T oriented for S6, S7, RS7. The common themes seem to be:
Finally, factory sport exhaust is out now as a US optional fitment with S8 Plus. Not terribly expensive for the three main pieces needed--less than typical performance aftermarket set ups. I think someone recently did the equivalent on an S6 or 7, but haven't seen even discussion for anything D4 about it. Sound wise, might compare to the most simple pull some stuffing/wadding out of rear most cans, which with access to a muffler shop torch costs nothing but some lift and torch time. I have never even honestly run into an S8 Plus on street, let alone parking lot, and no one has ever posted a side by side, first person experience type comparo of factory sport vs. non sport sound AFAIK.
There have been a variety of posts on the C7 boards I have followed casually in last year or so--4.0T oriented for S6, S7, RS7. The common themes seem to be:
Go into the center section and pull out the piece there which also has a (restrictive) cross over function to it. Don't replace it with straight pipes or the separate resonator type stuff because it relies on the crossover for the cylinder on demand function. If the exhaust flap is left in place, it's just like sticking the old banana or egg up the tailpipe joke/prank on one side. Thus replace it with a crossover X (or an H; pics and write-ups seem to be X ones generally). But some of the write ups say it tends to drone some with mods here. I often can't tell in posts for the ones that say no drone if it is legit, or wishful thinking. Drone is a non starter for me from old Audis where it got...old.
Go into back cans with even just a small slit and extract some of the wadding and then weld back up. Deepens sound and little other consequence.
Implicit, but I'm suspicious of anything that eliminates the rear flaps. Wasn't completely sure (skimming post so far and not delving into photo links) what was done or not w/ these here. Turbos are different than normally aspirated like D3, but on NA motors those are designed intentionally to increase back pressure at lower RPM's. You want back pressure on an NA for better low end torque. Flaps are best of both worlds for that since they open up with mid to high RPM's. But, I haven't seen much on how flaps interact with turbos and back pressure concepts. IIRC D4 flaps are only on one side now too? On D3 they were on both, but only one of two outlets per side. If true, on a D4 why in turn you dont want to omit the crossover function further forward but leave flaps in place. Apparently it sounds crappy in COD mode without flaps too, or at least that seems implicit in a variety of other posts from the C7 owners. That all distills down to leave flaps for COD, but need crossover of some type in mid area, whether X or combined can like factory or whatever.
Anyway, some info from other posts I have tried to condense conceptually. For OP, any feedback on these?Go into back cans with even just a small slit and extract some of the wadding and then weld back up. Deepens sound and little other consequence.
Implicit, but I'm suspicious of anything that eliminates the rear flaps. Wasn't completely sure (skimming post so far and not delving into photo links) what was done or not w/ these here. Turbos are different than normally aspirated like D3, but on NA motors those are designed intentionally to increase back pressure at lower RPM's. You want back pressure on an NA for better low end torque. Flaps are best of both worlds for that since they open up with mid to high RPM's. But, I haven't seen much on how flaps interact with turbos and back pressure concepts. IIRC D4 flaps are only on one side now too? On D3 they were on both, but only one of two outlets per side. If true, on a D4 why in turn you dont want to omit the crossover function further forward but leave flaps in place. Apparently it sounds crappy in COD mode without flaps too, or at least that seems implicit in a variety of other posts from the C7 owners. That all distills down to leave flaps for COD, but need crossover of some type in mid area, whether X or combined can like factory or whatever.
Finally, factory sport exhaust is out now as a US optional fitment with S8 Plus. Not terribly expensive for the three main pieces needed--less than typical performance aftermarket set ups. I think someone recently did the equivalent on an S6 or 7, but haven't seen even discussion for anything D4 about it. Sound wise, might compare to the most simple pull some stuffing/wadding out of rear most cans, which with access to a muffler shop torch costs nothing but some lift and torch time. I have never even honestly run into an S8 Plus on street, let alone parking lot, and no one has ever posted a side by side, first person experience type comparo of factory sport vs. non sport sound AFAIK.
Last edited by MP4.2+6.0; 02-26-2017 at 01:24 PM.
02-26-2017, 06:46 PM
#5
Audiworld Junior Member
Thread Starter
Replies and comments:
- The resonator was put back after I realized that it was not a restriction (because it was basically a straight pipe already. I didn't look at the crossover pipe just ahead of the resonator because I didn't see how that could be a restriction unless Audi really got sloppy.
- The "need" for back pressure myth has got to die! No internal combustion engine benefits from back pressure. Exhaust velocity, yes, but not back pressure.
- Each muffler was replaced with a mildly S-shaped mandrel bent stainless pipe. Each pipe tee-ed into twin tailpipes.
Mike
- The resonator was put back after I realized that it was not a restriction (because it was basically a straight pipe already. I didn't look at the crossover pipe just ahead of the resonator because I didn't see how that could be a restriction unless Audi really got sloppy.
- The "need" for back pressure myth has got to die! No internal combustion engine benefits from back pressure. Exhaust velocity, yes, but not back pressure.
- Each muffler was replaced with a mildly S-shaped mandrel bent stainless pipe. Each pipe tee-ed into twin tailpipes.
Mike
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aTOMic (09-24-2019)
03-01-2017, 02:31 PM
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thanks e-racer great info for me i've been researching this for a month now lol...i was actually going to remove the mid resonator now I'm not since it doesn't make any sense, i just want to tone up i little bit the sound before going to the track this friday
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03-02-2017, 12:14 PM
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by any chance anybody knows if 2014 audi s8 brings any type of launch control I'm trying with my left foot braking but i get it to 2k and then looses boost i think....any tip on that department will be highly appreciated since I'm used to superchargers or strokers but not turbos lol
