To get enough fresh air into the cabin, I installed a NACA inlet in the front. CAT ducting transfers the air flow to the cabin.
The inlet I used is the “902 MA-A” from ACS. Inside the cabin the “whisperflo eyeball vents” allow regulating and directing the airflow. Ducting is 2 3/4″. Since the outlet from the NACA vent is only 2″ I was not sure how to fix the ducting. The solution was the remove the filament inside the duct for some centimeters. With removed filament it is possible to fix the oversize ducting at the outlet, as you can see in the picture below.