Searching for a long forgotten article about airflow through the radiator (all about removing that hot air in engine bay of the rally car) I found the following article about testing flow restrictions (and verifying the results). Was a good read too.
http://autospeed.com/A_0629/page1.html
Oh, and he just happens to use an S4 as a guinea pig!
Very interesting. The article was kind of hard to understand but I think a turbo car is going to see a lot more negative pressure because the turbo is sucking in so much air. On an NA car, there probably isn’t as much suction. Also, I would think that improvements have been made since the old S4. The 8E boxes are substantially larger than the B5 boxes. Then again there is a lot more room in the 8E cars
I did the best I could while keeping the stock box. I removed the intake flapper, got an 034 smooth silicone hose, made sure my TB is clean, and I installed some DEI gold to keep as much heat out of all the plastic components. If I remember right, the A4 is pretty much the same design. I run an OEM filter
I think improvements could be made with the actual intake snorkel. If you look at it, it’s just provoking more turbulence than it has to. Right in front the air hits the wall of the snorkel and has to take a harsh exit stage left to go down the rest of the snorkel. Then there is the ridges that allow it to flex. Then there is that goofy metal structure where the two halves meet. Then worst of all to me is the sharp 90 degree turn it takes when it finally makes it to the airbox. Then again I have not tested it and nobody has every brought up the snorkel being a restriction, so I’m going off what I perceive
I like how he quantified with pressure drop