V6 XWD mufflers : the beauty is inside... - Saab 9-3SS Bulletin Board - Saabnet.com
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Quick summary : I was looking for a quick-swapping and cheap "sport" exhaust for my 2008 XWD that I track 5 or 6 times a year (winter and summer). So I bought a used 2011 XWD 4-cyl stock cat-back to replace the 2008 stock unit that is showing some internal wear (a 3 inch perforated pipe came out of one of the mufflers).
Yesterday, I did cut-open the top of both rear stock mufflers. What I found is very interesting.
1- Both of these mufflers are straight trough and they don't have any baffles at all. The mufflers are divided in the middle by a wall. The gas flow comes in the first chamber, where it passes through a perforated pipe surrounded by glass wool. This pipe then passes through the wall but stops there. The gas flow then expand in the second chamber, which is completely empty, and flow to the outlet without any obstruction.
2- Each muffler is different. The driver side unit is divided 50/50 with the wall right in the middle. The passenger side muffler is divided 25/75, with the bigger chamber being the first (front of the car).
3- The driver side unit is bigger in volume, and it is double-walled. And between each layer of stainless steel, there is a thin layer of a white insulating material that looks like paper (but it is not...).
Now I know why the car was sounding strange last summer at the last track day: the left muffler was completely blocked by glass wool as there was no perforated pipe in there anymore. The exhaust flow was pushing against the wool to expel it trough a 2 inch hole in the middle wall. The right muffler was ok.
Sound wise, I don't expect a huge increase in noise with the emptied muffler, but I did connect the inlet and the outlet together with some 2 inch pipes to make them really straight through. The open-top cans are now just there to support the brackets and to look stock from under and behind. If sound is OK, then I will re-weld the tops.
Anybody know the internal construction of the tiny "resonator" where the system splits in two? If it was just a "Y", there is no need for that stainless steel box around it.
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