[aspera]

Racecar Engineering had a great article a while back where they wind tunnel tested a BTCC car. IIRC, one of the curious things that they found was that the front downforce increased and drag decreased when they rolled the front windows down about 2 inches. I think it has something to do with air filling the low pressure areas behind the A-posts. I assume the air came from the high pressure zone in the cowl.

On my car, I have no carpet and all of the drain plugs removed. I get a nice breeze when I lower the windows an inch or two.

I've also spaced the rear of my hood (for cooling reasons) and noticed a change in pressure when I have the HVAC on 'vent'. Most of the air seems to go over the wipers and not pressurize the cowl area.

About a year ago I added window vents to my WRX. (The ones for a WRX are really slick.) They make slightly more wind noise when the windows are rolled up, but really suck out the air when the windows are cracked a bit. I can get by without using the A/C quite as much, and it really gets the hot air out of a parked car quick.

As you guys know, the WRX has a huge non-aero hoodscoop. Rally versions have roof scoops instead of A/C. That's a trade-off, but I've seen an even better solution on one of the RallyAmerica cars. The guy used ducting hose (think drier hose) to vent from the high pressure cowl directly on the driver.