Past regulations for Venturi tunnel dimensions?

[g-force_addict]

Where can I find past regulations for Venturi tunnels?
i.e. for Indy, IMSA GTP, Group C, even F1 when it allowed ground effect tunnels/sidepods.

I already tried to Google it without success.

Thanks guys.

[Sombrero]

If I remember correctly there were no regulations about the Venturi channel dimensions in F-1. They had just to fit within the max width, height and length regulations. After a while, there were some specs for the skirts before they were banned.

Group C : http://www.sportscars.tv/Newfiles/956.html

Most notably : "A flat surface area between the wheelbase of 100 cms (39") x 80 cms (31") must be an integral part of the chassis construction" and "no skirts, sliding or fixed".