Originally Posted by Plattus1000

I'll go look now... (looking)
Agreed, the info comes from Dinan. The airbox alone won't do much, also agreed. A good muffler will reduce back pressure but some back pressure or resistance is a good thing or you would see cars run 5" pipe from the heads more often. I run free-flow cat-back dual exhaust on my wagon and it feels faster but I also have a 3:18 rear end so comparing my last 540i to this 540it is n/a.
Cold air being denser hence a higher amount of oxygen per measure of volume, agreed but it being the case doesn't help fuel combust in a mist form more than a vaporous state. It lessens the overall mixture and surface area of the fuel, takes longer to burn and doesn't burn fully as it would as a vapor. (still looking)