Well, it seems that my M5 will not pass emmisions with its current Catalytic converter. The Nitrious Oxide level is double what is allowed here in Pennsylvania. My question is, what are the benifits of replacing the stock CAT with a high-flow cat? Has anyone had any experience with this? Also, any one know of a good aftermarket cat to look at? I plan on replacing much of the exhaust system with its European counterpart at some time in the near future, what does this do to my decision? Any and all advice will be greatly appreciated..................

Have good pricing on DEC cats. Worked great for me.

Mark - Thanks... I called discountconverter.com, they seemed to have a couple of differnet cats for my car. Unfortunatly, they new very little about BMWs.... I think I'm going to stick with an OEM Cat, from what I understand its allready high flow....

Discount is just a reseller. If you want to ask about the cat need to contact DEC directly. OEM are supposed to be best but damn expensive. I have had my DEC for 2 yrs ...ok so far.

I can find the oem for only about $100 more than the DEC, so I'll probably just suck it up and go for it.....

Thats great ... I paid $240 for the DEC but the best oem i found was almost $750. Would go oem for $100 if new

David - I have owned an M635 that was federalized, then returned to euro (exhaust) trim, as well as an 88 M5 that I put a euro system in (I'm in Canada). The euro system clearly helps, but if you must have a cat I've found the oem to be very good. I have the oem unit I removed from my M5 at about 50K miles (tested fine for emissions in VA at about 30K) that I would sell for about $250 if you are interested.