I used to have an Airaid MXP CAI (with tube)
It was set up so you could run the OEM 'rubber' inlet tube directly to the Airaid box/filter, or run the (supplied with certain kits) Airaid tube.
Moral of that story was the inlet diameter of the Airaid tube was the same as the OEM tube.
The filter base was ~6~ or so inches around, but they choked it down to match the OEM tube inlet diameter.
Never thought much about it, other than they made it that way to enable folks who didn't want to spring for the Airaid tube to use the OEM tube.
Saw some pics of the S + B and I see its about the same scenario,,, the inlet of their pipe is small compared to the end attached to the TB. Once again, a large diameter filter base reduced down to a small diameter at the airbox,,,
Not saying it's right, not sayin it's wrong, but it's obvious more than one MFG of CAI's does this 'reduction', so there must be some reasoning behind it.
As the S/B kit already comes with a replacement tube,,,, the reasoning behind this reduced diameter cannot be 'just to enable the user to not have to purchase a tube'
So,,,, why do CAI manufactures use a filter with a ~6~ diameter base and immediatley choke the flow down at the inlet end of the tube only to increase the diameter again before it gets to the TB???
CAI's are like that, but more than (1) is,,,
Also, is the inlet diameter of the S + B tube the same diameter as the inlet of the OEM tube?
FWIW, I think the S + B has a lot of things going for it, and its design / layout just 'seems to make sense'