Quote Originally Posted by Henry Rifle
.......The shroud on my electric fan has two rubber flaps near the bottom. If the fan is pulling, they are sucked shut. If the air "stacks up" at speed, they open and relieve the pressure. They have to be one-way, though.

It's kind of hard to see, so I outlined it. There is one on each side.
Yeah, when Cooling Components first came out with their fan/shroud combo they didn't have those flaps. A few years ago I noticed they added the flaps and asked them what they were for, and they said to allow more air through at higher speeds.

My fan/shroud has two flaps like Jack's, but I think on some of the larger shrouds I have seen 4 flaps, two at the top and two on the bottom.

I like the Cooling Components fan/shroud combo because it cools better at low speeds and in traffic. I do think I ran a little cooler on the highway when I just had my 16" Spal with no shroud.

I just pre-ordered one of their (Cooling Components) new fans from Walker at the Nats in Louisville. It has a larger (17") fan and a larger shroud, so I hope that allows a bit more air through on the highway. The larger fan is also not as deep, so it will help those who have clearance problems. It draws a bit more current and requires a larger relay, but that thing sure seemed to move a lot of air when I was comparing it at the show.