[kach22i]

Nice to see this old thread has some legs to it.

1. Older cars like my 1977 Porsche 911, and maybe even modern pickup trucks that lack rear wheel well liners will benefit from rear bumper removal and or speed-holes because they will actually be venting the rear wheel well pressure.

2. Trapping air to create a vortex air cavity (rear gate or rear bumper) requires energy. I suspect this energy need be initialized just once on acceleration. Therefore this energy surge is economized over length of cruising distance where it can remain static or stable. This would explain the acceleration testing "Logic" has posted.

Sidetrack: For an analogy think of the high initial amperage draw of an electric motor verses the continuous amp draw.

Racing, especially drag racing is going to be dominated by the initialization of air cavity pressurization prior to vortex forming. Best not to have any air-buckets in such cases.

I would love to see an air tunnel experiment or CFD graphic and or video comparing a bucket with into the wind verses opposite the wind. That is to say in example "A" bucket bottom towards wind, and example "B" annular opening towards wind.

To be a "simplified" example, removal to ring loop carry handle and top of bucket bullnose lip would remove unnecessary and distracting issues.