Ultra-lightweight and wind tunnel tested, our NACA ducts produce more airflow than the copy-cat NACA ducts you see all over the web. Our NACA's are designed, tested and QC'd at the Chillout offices in Atlanta and we know the moment you receive them, you will immediately notice the build quality is far superior to anything available online.
We'd like to point out that although our three-inch NACA's are excellent, moving into a four-inch model is at least 55% more efficient over a three-inch model. The footprint is nearly exactly the same so upgrading to a four-inch NACA shouldn't be an issue for most cars.
NACA ducts bring air into a vehicle with minimal increase in drag. The purpose of a NACA duct is to increase the flow rate of air through it while not disturbing the boundary layer. When the cross-sectional flow area of the duct is increased, you decrease the static pressure and make the duct into a vacuum cleaner, but without the drag effects of a plain scoop. The reason why the duct is narrow, then suddenly widens in a graceful arc is to increase the cross-sectional area slowly so that airflow does separate and cause turbulence (and drag).