Background: I have both the pre-and post-flap ducting connected (ie: with the flap closed I'm drawing air from behind the left side of the bumper, but not with any sort of ram effect). You can see the termination of the post-flap intake duct in some of the photos above.
Tonight, on my drive home, I datalogged at a reasonably constant speed and rpm (~3500rpm, 5th gear, ~65mph) a drive with the flap open (briefly), then closed, then open again. At this constant speed and engine load, I saw an 8*C (14*F) in 1 minute, 15 seconds, with most of the drop happening in the first 15-20 seconds. This is a rather impactful change! Definitely more than I expected, as I already had a low temperature air source and I didn't see this behavior before doing the duct.
In the stock CSL firmware in sport mode the flap opens at 3300rpm in gears 1, 2, 3 (41mph) and at 40mph in gears 4, 5, 6. Seems logical.
Vertical yellow bars in the datalog below are when the flap opened/closed.
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