[brucepick]

Thanks Chaz.
Do you have other pics of your kamm back? Did it help FE?

The concept I'm trying to execute is actually the same as in the pickup truck where som can have better aero with the tailgate up than with it down. The pickup bed sets up a swirl pattern, probably an area with increased pressure. And the airflow over the cab skips over the bed and then over the tailgate, with a resulting smoother air flow than with the tailgate down.

So I'm hoping that the air flow off my roof skims over whatever turbulence sets up between the side panels. And then exits off the back edge of the spoiler, almost as if I'd instead installed a template-shaped "kamm back" that starts around the roof edge and ends up about 6" above the rear bumper.

The side panels hopefully do two things:
1) Guide the air flow from the side windows area slightly inwards towards the center line, so it exits with a smaller cross section.
2) Keep some air between the side panels so it will have some pressure so the roof airflow will skim over the spoiler's rear edge.

Don't forget - the air can't really follow the dropping roof line and the even steeper dropping rear glass. Yes there are tuft photos showing mostly nicely lined up tufts but I'm convinced there's a big vacuum being sucked behind the rear glass, because it's so much steeper than the template line.

Yes it's a challenge to build this thing so it works as intended. Especially so because you can't see the air. Real tuft testing requires probably two friends in a truck to get the photos. In other words, I think tuft testing is easier said than done.