Stock S2 Back Box what's inside (pic heavy)

[s2_wot]

I decided to explore the internals of the s2 back box to educate myself. Audi had been making exhausts for turbo coupes for 15 odd years before they got to mine so it seemed like a good place to start.

I wanted to see how it was constructed, was it chambered and did it look restrictive etc.

On the ground and after 10-15 minutes with my weapon of choice:


1st layer of steel removed:


2nd layer of steel (stainless this time) removed:


At 1st glimpse we have 2 chambers both packed with dense glass wool type material:










As we get closer to the flow path of the exhaust gasses the material changes to a steel wool type material:


Anywhere there are perforations the steel is wrapped in this type of fibre:


1st Chamber revealed:


2nd chamber all wrapped up, this is 2 individually wrapped perforated tubes:


The chambers are seperated by a 5-10mm gap:




Overview with most of the packing removed:


Inlet Chamber close up:




Outlet Chambers close up:

[Le S2 Audi]

Very Interesting.... Never had one to bits before!!

[Sonic]

Interesting stuff! Not sure i'd have been picking up that wool stuff with my delicate bare hands though

[Error404]

interesting, thanks for sharing.. can see why they're so fooking expensive now!

what is the function of the gap / divider between the first chanber and the outlet chmabers then?

[s2_wot]

interesting, thanks for sharing.. can see why they're so fooking expensive now!

what is the function of the gap / divider between the first chanber and the outlet chmabers then?

Here's my thoughts but would like much imput from others.

Sound waves enter the 1st chamber where a quantity of them go through the perforations in the chamber as the gasses turn through 90 degrees. These waves bounce around in the sound absorbtion material to their hearts content but don't get to the 2nd chamber unless they go back into the path of the exhaust gasses.

When the exhaust gasses pass into the 2nd chamber there's another opportunity for some sound waves to go through the perforations into more sound absorbing material.

The idea with the 2 chambers is it prevents the sound waves from interfering with each other as they are being dampened.

The really interesting thing for me is that it's not very restrictive, that'll be difficult to improve.

Any ideas why there are way fewer perforations in chamber 1 vs chamber 2? That one has me a bit confused.

[newsh]

Have a play with this

http://www.falstad.com/ripple/

[david]

[QUOTE=Error404;540189]interesting, thanks for sharing.. can see why they're so fooking expensive now!

[s2_wot]

Have a play with this

http://www.falstad.com/ripple/

That's too much fun

[newsh]

Yep

[andy10v]

Very interesting. Thanks for sharing.

[pixsaudisex2]

Cool..

[martinws]

interesting to see. Always thought of doing that. I hope that box did not contain asbestos.

[s2_wot]

interesting to see. Always thought of doing that. I hope that box did not contain asbestos.

Ah I don't think so.

I'm going to make a 3.5" OEM+ for the craic in stainless but not double skinned. It has to flow better than any of the generic ones and be more effective.

@newsh, I'm addicted to that software, spent about 2 hours drawing it last night. Exactly how I'm going to form the box into a 3d parabolic curve I don't know

[newsh]

Its amazing how you see the cancellations happen when you change the shape and add holes etc. eh?

[s2_wot]

Click the import / export tab with that program open. Delete the stuff thats shown in the pop up window and then copy & paste the entire contents of this attached document. I think you have to press save / import. When you look at it in 3d it's amazing how much of the noise is cancelled out.

You probably knew that already...