Originally posted by Emission
A 10" SPAL fan will pull 1070 cfm through the intercooler (out of the engine compartment). Add that to the cfm the engine fan is pulling in (3000+ cfm?)... and you have quite a few cfm's that must be pulled through the opening in the grill (or from other "leaks"). The way I see it, that's a lot of fresh air.
* You are getting cool air into the intake.
* You are getting cool air into the engine.
* You are getting cool air through the intercooler.
Sure, it is a bit more complex, but I really don't see where the logic fails (I'm not a scientist, so tell me if I am nuts).
With the open grate blocked off so all air is forced through the intercooler, the intercooler would benefit, but the engine and intake would be taking in "post intercooler" warm air.
1070 cfm may seem like a lot, but at speed?
The empiric test by Jim on the first page suggests that there is a top to bottom gradient across the IC (with the pass side blocked). This suggests a little down force, not just an absence of lift.
Taking air from one side of the tea tray to the other makes little sense to me in terms of pressure (what you posted at the top of this page).
The engine fan is pulling some air through the IC if there is positive top to bottom pressure, and certainly could be "helping" if it was completely neutral pressure gradient. Therefore, Craig's idea of a pull fan below the IC (top to bottom flow) makes some sense.
Is the ambient air that much hotter after going through the IC? If Craigs temps are to be believed (I don't see why not) doesn't sound like it. Furthermore, aftermarket (larger IC's) tend to lower engine temps at least by oil temp, suggesting the gain from charge cooling outweighs any potential negative (in heat terms) to the engine cooling air.
It seems that it would take a heck of a lot of machining to close all the holes, and huge volume fans (unless you added radical skirts/front spoilers), to suck the air from below the car up on top of the teatray to create really prominent downforce.