Thanks all. These comments are helpful. I do have an electric fan. It is a two speed 16" with full shroud on the inside. Part of increasing the mileage involved wiring the fan with two different thermostats so it comes on the low speed only first, and then uses the high speed only when it gets really warm.
Given this feed back, I think I will plan on partitioning the inner cavity between the grill and radiator so the air that comes in through the open center section can only go through the radiator. The two outside sections I will simply block off from behind. What is barbecue black material? Is this a product I can buy that is already black, or is it paint? I usually fabricate my parts from aluminum or ABS and then paint. There is another thread that shows the front partial belly pan I have already built.
This will not actually be that simple as I might have to remove the bumper in addition to the grill. This means taking off the belly pan and airdam as well.
If you look at the photo carefully you will see that I sealed off the space between the hood and grill so no air can enter there. This si cooredinated with a pair of aluminum panels that keep the air which enters the grill from going over the radiator That was intended to force the air through the radiator for cooling, but I can see now it will make the grill block more effective. Here is a photo of those panels.
The coil is on the fender,but that is actually cooler than the engine block mount that was stock. The BMW M3 vents in the fenders are functional. They are there to try and cool the coil as well as the HEI module that is also on the fender. It is mounted to an aluminum sink.
There is another thread on the forum showing the partial bottom pan and air dam from below. I am eager to figure out how to design something more extensive that will not compromise the "look" and not complicate service too much. Thanks again. This is fun.
Sam