There are really two kinds of heat problems to solve. If the car is running hot on on the freeway or the track, a fan is going to be of negligible value. For that, you need some kind of scoop (either the Pelican, side-light-marker kind, or a fabricated lower scoop), and a shroud above and around the cooler to keep air moving where you want it to move.
For the stuck-in-traffic variety of overheating, the ducts won't do you any good. You need a fan. I use a Spal fan connected to a switch on the dash, next to the sunroof switch. You can also get a heat-triggered switch, but you probably want to also be able to override it. I think there's a Pelican technical article on wiring the switches.
The only significant diffrences between fans is how much learance they need, and whether they're pushers or pullers. I have a pusher, mounted on the headlight side of the cooler, away from the wheel.
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Jack Olsen
1973 911 T (3.6) sunroof coupe
jackolsen@mediaone.net
[This message has been edited by JackOlsen (edited 03-23-2001).]