Quote:
Originally Posted by Used2be
If you look through the Exhaust System Database at the beginning of this part of the forum you should find all the variables available to mix and match exhaust system parts. BMW does make sleeve clamps so we're able to cut the stock one-piece exhaust to replace some parts of it. I've also read that primary/secondary stock cats are in the downpipe, but have never seen a cutaway image to prove that. You'd think they'd want both cats between the sensors to have an accurate sample of the exhaust gasses, so I believe they are in the downpipe.
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From my visual examination of my car it seems there's only one set of cats.
I cant be sure if primaries and secondaries are mated together but I can tell you I only see a single set, the downpipe.