I'm trying to delete my cats with probably the supersprints replacement pipes... I wanted to know if this could be done with the stock headers intact... I've spoken to a few people who informed me that the cats are built into the headers and, so therefore. replacement of headers will be in order as well.... Others have said that just the pipes would be sufficient... Also I'm trying not to get a Check Engine light so i could pass inspections... Has anybody ever done this mod yet... Any performance gains(please say HELL YES)??? Is Eissanmann better?? :help

If you have a US-spec M3 the cats are part of the headers, so you will need to replace the headers. If you replace them you will get a CEL unless you run software that disables post-cat O2 sensor monitoring.

well im not positive on this as im more in tune with the E36 world, but you probably wont get any gains out of it. BMW makes their exhaust systems pretty well, so im sure deleting the cats themself wont provide much if any power. the other pipes however should provide gains...but i wouldnt look for anything HUGE

In the E46 M3, there are gains to be made since the US headers are different than the Euro headers. Double digit gains are not unheard of.

The very first E46 M3 in America to break 300 rwhp was a guy who put euro headers and euro cats in, and custom software. Euro headers fatten the power band up quite a bit, plus it gives the exhaust a beautiful sound. I think the gain at peak is only 15-18lb-ft, but the peak gain is more like 30lb-ft.

The exhaust isn't made by BMW, its made by Arvin Meritor, a subcontractor. The only reason the US headers have cats in them is so the cats heat up quickly and reduce cold start emissions. If it didn't have a noticeable effect on power, BMW AG wouldn't have had a seperate design for euro-spec cars.

I had euro headers and cats on my 2002 M3, and my new 2005 is going to get Evosport headers with no cats.