I have done some e46 header testing my self also. For e46 m and non m. I'm not sure why some are freaking out about dyno numbers. It's the same header upgrade that people have been doing for 10 years. You are looking at 10-20 hp depending on the condition of your own vehical. If you are promised more than that there is likely some fine print because this is reality. The choke point is the merge and the cat. You eliminate those obstructions and you get your gain. Fitment is the only issue worth being concerned about. If you can accurately sense 3hp plus or minus then quit your job and become a live in car horse power moniter yourself.
sent from my ATARI sc1224