I just bought myself a little handheld anemometer. I took out one of the plastic plugs behind the bumper and duct taped the meter into place in the front trunk. Went for a little drive. Here's what I found...
At 40 MPH, I was getting a wind speed of 17.5 mph in the hole. Converted to CFM, this is 25.718 CFM. Not bad for one little hole. The bumper was still in place and the LE airdam was still installed as well. Next I'll test a stock valence.
Just sharin. Oh, BTW, the air pressure was 4 bft. I don't know what that part means, but there it is.