[Christ]

winkosmosis -

The paper you linked suggested that you were expecting the holes to act as an underbody diffuser, to increase rear downforce, when it would in fact not happen that way.

IF the holes did anything positive, and I have my doubts, it would be nothing more than lessening the effect created by a parachute of the rear bumper area. I still have ill feelings when I think that even that could be achieved without doing more harm than good. Airflow doesn't like to be redirected, let alone through jets that would increase the pressure of the flow. If you're forcing air through a smaller area than it's already in, you're increasing its pressure. The energy required to force the air through the smaller area has to come from somewhere. Your car's inertia provides the energy.

I *once again* agree with you about cutting the bumper to remove the overhanging area and combine it as a flat upward slope from a lower section of the body. That would be the definition of a rear belly pan, though, only modified to remove the same section of the bumper that we would normally just cover up.