I have been reading about the F1's now illegal "Blown Diffuser" and now know .001% of everything there is to know about them.
Anyway. If you put the naca ducts on upside down, they do exhaust air from the engine compartment to the bottom of the diffuser, as verified with my trusty yarn tufts and my HD Wing Cam (think cheep GoPro) and a quick test drive.
My .001% knowledge says:
I am still getting cooling in the engine compartment due to air flow.
I am getting more, and even better energized, air flowing under my diffuser (faster air flow under a diffuser is better).
I may even be getting the advantage of the naca ducts acting as vortex generators keeping the laminar flow better connected to the steep (for a diffuser) angle of the diffuser.
Mentally, I figure this is worth 4K to 5K pounds of additional down force.
In reality, not sure its worth any:shrug:.
Either way its easily reversible and cheep to test.