Hey Jim
On a NACA duct, you want that shallow sloping base and walls curving larger as you go inward right? Perhaps the boxster duct sorf of qualifies...
but the whole naca duct thing is supposed to get you faster flowing airstream that is above the boundary layer so you get a higher pressure going into the duct
if I remember my fluid dynamics correctly
(which I may not!)
of couse with the "ram" intake (protruding outward rather than inward), you get higher form friction, but I bet you still get a decent pressure in the duct.
I imagine it is no better or worse than stock. It would be interesting to test it on a flow bench and measure the duct pressure.
but I did the ducts for looks too, not function. I have always thought the stock boxster ducts were one of the biggest compromises Porsche made from the concept version in 93, with the ducts low near the bottom of the rear fender ala Ferrarri. That looked SO much better IMHO than what they did in production.
I think the 987 version looks even worse with the exaggerated verticality.
Were the concept car lower ducts too expensive? Too hard to make? I wonder....you see how they did it on the 911 turbo, now those look like real NACA ducts