Has any one tried shielding off the back side of the radiator with some type of metal sheeting to force the exhaust air from the fans to go downward to the underside of the car ?.

 

Why? it will go there anyway. And its not a good thing, causes high pressure under the car which = lift. But you have to live with it.

Actually what would be best is to make a duct in the hood and duct that air out over top of the car do reduce lift and give a little better front downforce.