Explain venturi tunnel design (downforce) on race cars

[FrankTHutchens]

I've tried to find info, but nothing that gives a crystal clear idea of their design. I know that they speed up the air to result in less pressure/downforce, but I'm not sure whether they narrow vertically, or if they all have an upside down wing-thing going on the inside roof of the tunnel?

I've seen depictions of the walls narrowing; and I've also read how the exit from the chute has its' height regulated to limit downforce.

Does the venturi tunnel have to interact with the ground through skirting etc. to work, or could you just have a section under/along side the car enclosed on four sides achieving the same end?

If you know of any good websites about this, point me in that direction please

 

[funnelguy]

Check out this site, especially the recommended reading list.

http://www.mulsannescorner.com/