I drove it around yesterday evening and this morning, coming back today I drove a bit in the rain. I found that driving on back roads during testing, and in the rain today led to some interesting observations. I definitely have quite a flow back into and under the kammback. After a little bit of coastdown testing on some country roads, here is the way some of the dirt settled inside of the kamm.
You can see how the dust/ dirt settles on the inside of the aluminum frame. It got a lot worse after a bit more driving but I didn't get a picture of it, this was just driving to my test area. Which to me seems like air is moving into the low pressure zone under the kammback. It also happened while driving in the rain, I got serious mist underneath of it which settled on the bottom half of the back window, about 2/3rd the height of the kamm opening, and at the beginning it actually settled in a semi circular shape matched to the opening at the rear of the kammback. This mist and water under the kamm almost completely killed any rear visibility!
I wonder if/ and how much this forward moving flow under the kamm might be hurting efficiency. Which is where my main question comes from,
do you guys think that there is any advantage to blocking off the vertical opening at the rear of the kammback?
The visibility problems to me right now are not worth the small gains that I have seen so far. However, if blocking the opening might help efficiency and stop water mist from flowing in, I might leave it on.
I can usually get about 185 km at the 3/4 tank mark on my fuel level gauge. Today I got almost exactly that again with the kamm on, and part of the drive was cooler temps and in the rain, so it does seem to be showing some improvement in real world driving.