[Phase]

Originally Posted by aerohead

* are they referring to plan-taper boat-tailing on the sides of the car? That WOULD reduce the wake, as well raise its pressure.
* On top of the car, all centerline flow is lost at the forwards spoiler.
* The secondary spoiler is almost completely in the turbulence of the forwards spoiler, except for it's outer edges. You can see it in the wind tunnel videos.
* The tearing edge of your spoiler is exactly at the aerodynamic streamlining template- # 3 contour. It's what guarantees flow reattachment on top of your car. It's nothing like a Gurney flap. Those are for direct downforce. You have no need of that. It's induced drag.
* The tearing edge of the OEM spoiler reaccelerates the flow, lowers the local pressure below 'adverse', provides only for reattachment, capturing a locked-vortex ( separation bubble ), which is what allows pressure recovery from the local streamline flowing over the 'bubble', creating higher base pressure, and drag reduction by 'mending' the flow.
* Your box-cavity, or boat-tail would just continue the imaginary contour defined by the template on top, the side plan-taper would respect what's already there, continuing the imaginary elongation contour there, and the 'slow' diffuser would reduce the wake from below.

so youre saying like this? it just seems weird for the sloped roofline to go down, then flatten out into the spoiler, then slope back down. a bit wavy?