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.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas