@psoutzis, if you feel I am hijacking your post, tell me, I will open a new one, but as it is still about concept and design I think it's ok to go on...
nicklouse, thank you for your comments!
My idea is to get the coolest air to the engine to improve its density. without the box it would suck quite hot air as sitting just above the exhaust.
Plus the box's job is to avoid having too much turbulences around the intake.
I know the rear side of the box is quite close to the mouth of the ram pipe, but hey, I have to deal with the original concept of the Mini ;).
At the moment I have 100mm between the hole and the axis of the ram pipe. Isn't it enough?
Even now, I fear the box is already too big for the bulkhead clearance...
My assumption at the moment is, looking at the original elbow for the HS4, this one is about 50mm long, so I cannot go bigger as the elbow is already auite close to the speedo hole.
As my car is an LHD, I do not have the clutch and brake master cylinders in the way on the right side so I could go further with the intake of the box, although would it flow better?
I do not have a flow simulation software, to be honest I didn't look for it.
What I forgot to mention is I am playing with the idea to build a small homemade flow bench as a side project (not sure how effective it is) to try the different setups I showed.