Hum this is where there is a difference with WCMA. WCMA never mentions the silhouette aspect of the rule. It looks like any forward facing duct has to make a 90 degree turn, wherever it is located:
From the WCMA technical regulations:
"
h) Forward facing air ducts may be installed for the purpose of delivering cooling air directly to the
engine, cylinder heads, oil cooler, and/or carburetor, provided the ducted air makes a 90 degree
bend within the bodywork. Air duct openings may be located within the cockpit area, and/or
penetrate the firewall, provided the duct is baffled or the firewall is extended to prevent flame and
debris from reaching the Driver. Any shape may be used to form firewall extension. Any other
firewall inlet shall also prohibit passage of flame and debris. (Recommend: that ALL of this
extension be the same width as the firewall, allowing for bodywork contour limitations, and extend
in a horizontal plane back 2in, minimum, past the carburetor body.)
"
FV80 wrote:Jean,
ANY duct that faces forward is a 'forward facing duct' - so, yes - NACA ducts count. The intent of the rule is to NOT allow a competitor to put a forward facing duct within the silhouette profile that allows air to simply pass through the car, therefore reducing the effective frontal area. Back in the early 80's a competitor (specifically Don Courtney and the Vista Bushwacker - followed shortly by Jerry Knapp and the Lazer) built a car with only the OUTLINE of the fan shroud covered by the bodywork (looking from the front). The fan shroud COULD be installed "within the bodywork" (the way the rule read at the time), but it did not stop the air from passing through that area instead of around it. The result of that, after about 3 years of living with it, was the introduction of the silhouette profile picture and the addition of the duct verbage to the rules. If the duct is outside of the profile area, it is free.
Steve, FV80