[spacemanspif]

The air dam needs to be placed directly under the radiator, so basically right on the core support. With 100% sealed front end you'll also want to make up a "skid plate" or belly pan under the nose of the car to reduce turbulence and control the air a little better. Start your design where the belly pan seals the entire area from the very front of the car back to the air dam. Then cut a hole in the pan that is maybe 18" wide and 6" deep. That hole will be where your cooling flow comes from and the rest of the pan and dam will encourage the air to exit the car off to the sides. The dam should be as wide as the car if possible and do double duty blocking air in front of the tires. You might want to consider creating a tunnel or channel in conjunction with the core support so that all the air coming into the engine compartment HAS to cross the radiator. Since air will take the path of least resistance there is a good chance that without the channel most of the air will flow around the radiator and just cause more turbulence.