What about exhaust blown venturi tunnels?

[g-force_addict]

Of course for racing series that allow venturi tunnels.
I wonder why these series don't use them? (as far as I know).

Would they benefit from a floor level exhaust outlet in the same way as a exhaust blown diffuser does?
If not, what would be the optimal exhaust placement?

[flynfrog]

they have been used in the past but they were sensitive to throttle position. They didnt have the blowing maps they do now though.