Quote:
Originally Posted by MHR1294
To OP
I had a 2001 Volvo V70 T5 which had a high mount spoiler with a "hole/slot" in it.
Interesting thing happened, you could see the giant swirls in the mirror generated when it was raining in the spray. You could see 2 big swirls forming on the rear window coming down from the upper middle an spreading out. So looking from the rear, that's clockwise on the left and anti-clock on the right.
With the hole covered up, the dirt left on the rear window was more uniform spread. Fuel consumption was a little bit worse too, however the scale only reads to the nearest 0.1mpg (imp) so 0.4mpg improvement might not be as significant when you take in other factors.
so, I don't know what it was doing, but it was definitely doing something. 
Perhaps it's performing a similar function on the fiesta? |
Interesting. Trailing vortices that rotate (viewed from behind) clockwise on the left and anticlockwise on the right are indicative of the body developing lift.