I'm gonna try a link to Walter Korff's cooling system schematic
Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - aerohead's Album: Book illustrations - Picture
Here is the internal architecture of a diverging duct.If the walls curve too steeply,you have internal flow separation.
http://ecomodder.com/forum/member-ae...tbody-car.html
Here is Hucho's table for 'optimum' noses.
http://ecomodder.com/forum/member-ae...iguration.html
If you'll compare the Nissan's nose,you'll get a feel for how to proceed.Your inlet can be only a fraction of the height of your radiator if your inlet duct to it is as deep as the height of the radiator,as wide as the radiator,and airtight construction.
I added a little more nose to my truck to get the depth of the duct equal to its radiator height.I'm cheating on width,but so far no problems.
