Thanks for pointing that out RB. I've been looking at headers for a while and the 02 ports were something I havent even thought of.

^If I didn't have emissions testing I'd definitely fit them, but by the time I get cats welded in (they'd have to be small) and everything else I hate staring at CEL's - I haven't read from anyone who fitted cats onto these headers and were CEL free

Yup, I would prefer an install with no CEL too.

I do get tempted when people post their installs though!

You just need to get the right aftermarket cats for the application, and weld in O2 bungs after the cats for your post-cat O2 sensors. Alternatively you can leave the post-cat O2 sensors physically before your aftermarket cats in the exhaust flow, but add spacers so that they're further from the exhaust stream and thus see lower values. It's definitely possible to do headers without a CEL.

What is "cel"???

Check Engine Light

If the goal is better sound why not just change out the muffler, resonator and/or add an X pipe? Headers will change the sound some but not near as much as downstream exhaust work.

Installing headers even on what they were designed to fit is seldom problem free. Even if your goal is to improve performance headers would be way down the list of least spent for greatest gain.

Sound and performance, i want a deep sound, and what abour the mustang injectors??

Unless you relieve some back pressure the headers will do very little for performance. As I mentioned, headers won't deliver much change in sound. The cheaper and more effective way to reach your goal is to modify the exhaust. That will improve performance some and get you a different sound. I don't know how or if you can make it sound deeper. I have done no exhaust work on a 3.0.

Assuming you are referencing larger fuel injectors used for a Ford Mustang they are not for a BMW. Also there is no need for larger fuel injectors unless engine mods require more fuel than the existing system can deliver. As a general rule that takes a lot of engine mods. Your existing fuel system is fine.

If you are referring to the mustang injectors for the better spray pattern look at e46 fanatics they have lots of info on it. My thought is if I'm that far in with my miles I'd do them but I'm really hopeful that by that point I can go force fed. Jon