NACA ducts do not flow much air. One lister hooked his air intake to one NACA duct and the lack of air flow choked off the carbs at high rpm. They look cool and do flow some air, but not that much.
Curious - do we have any numbers on this?
I've previously calculated the inlet area of the 47/Banks NACA duct and it's 20% greater than the area available from 3" dia trunking.
I was thinking to utilise one duct to feed a commonly available flat panel filter box with trunking to a 2xDCOE mounted air box.
The consideration there was not so much air flow, which as you say is perhaps not much, but merely to access to the ambient air stream. In that respect, a simple hole in the bodywork would be fine.
With that said, the 47/Banks NACA duct looks weird. For anyone who's read the rather long and esoteric NASA article on submerged ducts . . well, I can't see that it's even long enough.
I also wonder if one couldn't mount a counter argument and suggest that a Bernoulli effect might be in play and that the duct actually extracts air due to it being somewhat at an angle to the air flow! I dunno.
I'd like to see a wool tuft video on that duct.
On oil cooler mounting, I thought David A's installation looked promising. (pic below)
