407: I can't comment on airflow because I didn't attempt to measure it. What I can say is:
1) The value in doing this is to improve recirculation. If you consider that 75% of the overall perforated area (used for recirc air from the drivers compartment) is blocked, this has to help.
2) If you aren't running the AC in recirc mode, then you are still sucking in a lot of hot outside air
3) On my ride home yesterday, it was full sun, 95 degrees, 50% humidity with a THI of 105 (as per WeatherBug locally). Last year, on similar days, I would be warm with a level of sweat on my back by the time I go home. Yesterday, within minutes, I was nearly cold. I stopped, rolled the windows down while I went in the store to bring the temperature back up. Got in the car and again, within minutes, was nearly cold. Keep in mind that I have only full blower speed. What I didn't do was try to see the differential of with and without running recirc mode.
So, my sweaty butt seat of the pants answer is the increased recirc airflow makes a big difference. Your mileage may vary!
Last edited by yellowvert; 06-12-2012 at 01:58 PM.