Ram Air Hood Scoop Calculator
NACA Ducts may be used in the motorsport industry as a means of providing efficient air flow to the engine. If a hood scoop is postioned correctly, away from significantly disturbed airflow, an estimate of the pressure rise may be calculated by inputting the vehicle speed as below.
NACA Duct Equation
Pa         = Atmospheric Air Pressure
Density  = Air Density
Speed   = Vehicle Speed (mph)
  Speed Mph
 Pressure Increase (psi)
 Percent Increase (%)

The above NACA Duct atmospheric air pressure conditions are taken at International Standard Atmosphere i.e. (ISA, 15 Deg C, 1.01325 Bar).

The NACA Duct pressure increase needs to be corrected for significantly hotter or cooler air temperature conditions.

References ::
Wallace Racing
Race Car Engineering and Mechanics, P Van Valkenburgh, ISBN 0-9617425-0-X.