Earlier in the thread Grubby said this:
“A scoop like on Cobras will actually have air pushing out from the engine bay at speed.
There is much more surface area in the nose than the scoop. Thus more air pressure pushing in the radiator than in the scoop.”
I’d like to talk a little about Grubby’s assertion and separate the two elements:
1) area of the Cobra nose opening/radiator measured in square inches
2) pressure/air flow due to forward movement or fans
The area of the Cobra’s elliptical nose opening is approx. 225 sq in.
My aluminum radiator finned area is 330 sq in.
But a typical radiator only has 33% effective open area which equals 110 sq in.
(forgetting for a moment air friction and turbulence as the air moves through the fins)
But in front of my radiator I also have two fan motors and two five bladed fans all totaling 140 sq in of obstruction. (forgetting about the splitter and
oil cooler fittings and hoses protruding into the opening)
So I actually have more obstruction area than radiator effective open area.
So lets spin the fan blades to create air flow/pressure and zero out the obstructive area for the blades.
Net net I have 205 sq in of nose opening trying to pass air through 110 sq in of radiator effective open area.
Now a typical electric puller fan (let’s say a fan rated at 1800cfm if you have sufficient voltage and your wiring/relay are rated correctly) has a 33% efficiency drop thru a 2 core 1.5” radiator (55% loss thru 3 and 4 core radiators).
Now you’re depending on the fan at low vehicle speed to supplement air movement through the radiator vs air movement through the radiator at higher vehicle speeds.
So where is all this air going?
The side vents amount to 80 sq in and the area in front and around the side of the engine amount to another 200 0r 300 sq in. So there is a lot of room for air to exit.
Now, I can imagine with a car standing still, and in the absence of the venturi effect of air moving under the car in motion and drawing air out of the engine compartment, and with the fans running, air could be coming out of the hood scoop opening.
If I’m sitting at a stop with the fan running and I reach forward on the side of the car towards the side vents, I certainly can feel a lot of hot air coming out.
And if I reach down the side of the car towards the ground (my car is a street version – no side pipes) there is a lot of hot air exiting from under the car.
So there is a lot of air movement out of the engine compartment when stopped.
The air movement into or out of a hood scoop?
Well my thoughts are this: the hood scoop opening is 17 in x 2 in which equals 34 sq in. Keeping in mind the radiator only has 110 sq in of effective open area so the hood scoop adds 33% to the air entering the engine compartment.
On top of that, the air entering the hood scoop is at ambient, let’s say 75 deg, while the air coming through the radiator has been heated to, let’s say 185 deg.
So a hood scoop will be dumping 33% more air into the engine compartment at a much cooler temp.
That’s why a turkey pan works.
Now my car is a street version with two 4bbls and no turkey pan/cold air box.
So all that cooler air will be bathing the carbs and top of the engine in cooler air as the car is moving
So until I get a hood scoop on the car and do a tuft test, I won’t know how effective it will be.
My guess is it’ll work just fine.
Stay tuned.
Cheers
Greg
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