[RedDevil]

Hi, and welcome!

In aerodynamic work the main area to improve on to reduce drag is the middle to aft area. The front does not matter much - the air has to be pushed aside to let the car through anyway.
So you put your attention to the right area

Now most cars today have their roof line gently curved down towards the back.
The reason it is curved down is to reduce the wake by making the air reposess some of the area it was pushed away from.
The reason that curve is gentle is to ensure the air does actually follow the contour instead of breaking free in turbulence, which would defy the concept.

One problem is that any change in direction causes a low pressure area (or more correctly, you need a low pressure area to make the air flow change direction towards it).
Such areas are inherently unstable, if air can flow towards it from the sides it will.
Make a nice curved roof on a car with flat sides and air will roll from over the sides to the top with nice vortices etc.
So to prevent that it is best to taper the sides too.

One good example of an optimized taper can be found here: http://ecomodder.com/forum/showthrea...ion-21952.html

As I said, the roof often shows more curvature than the sides.
So your idea might work if applied to the sides, where it is needed more.

For instance, make the rear side windows taper slightly inside to funnel some air along the inside of the rear quarter pillars to slots inside the side edges of the back window.
Or by channeling air from the side to the rear wheel wells behind the wheels and out through holes in the rear bumper or something like that.

Anyway, I like the channel (funnel/duct!) idea and hope this thread will reveal if and where it is used on cars other than front bumper to front wheel well - we know all about that from MB and several sports car manufacturers.
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