Originally Posted by IkirisTheX5

I wouldn't add headers unless they were a name brand that lists gains. It doesn't mean the claims will be accurate but that is why they build headers. The gain with the right exhaust isn't much. As an example the Dinan free flow muffler for a 3.0, when it was available, increased the HP by 5 at 6500 RPMs and TQ 4 also at 6500 RPMs.

Also bcredliner: the headers I was interested in are definitely not manufactured by a name brand, but from what they claim and I’ve read they are pretty good knock offs of the Supersorint E46 M54 headers which are equal length and claim to increase power by 20hp on a 330i. Yes, there are fitment issues regarding the O2 sensors and bolting up to stock exhaust, but those are the same complaints I hear about the $1,200 authentic ones as well and can be worked around fairly easily. Everyone says they bolt up to to the head just fine, which if they didn’t would obviously be a deal breaker. In summary, they sound kind of annoying, but effective and at 1/10th the price of the genuine ones still very tempting to try.