Originally Posted by Mobius
I'm curious as well as to the details that enable fans to be effective when there's 75mph constant airflow. Was that 75 cruise, or WOT?
75 mph cruise. Basically, running down the interstate. Now, we've got high ambient temps and low ambient pressure with low humidity, so it's pretty much a worst case setup. But it's very repeatable.
Again, 75 mph on the nose is not 75 mph through the radiator. Considerably less. You can try to improve the ducting to ram more in (this car had typical street car ducting behind the factory nose, including a "scoop" behind the IC to try to ram air into the rad) but with that high pressure underhood you start reaching limits fairly early.
With improved airflow across the rad - specifically, extraction from underhood - I can see the shroud starting to become more of a limitation. On this car, I'd tried running a single fan, no shroud, etc, etc. But it was the airflow kit that made the biggest difference.
I understand this is a race prep forum, so your mileage may vary depending on what holes you've cut where. Anyhow, I've seen proof that fans do help at speed and thus our statements to that effect.
Interestingly, I spent the weekend at High Plains Raceway with the big V8. Same basic setup including the fans and shroud. 90+ F high altitude ambient, nothing extreme on airflow management. No heat exchangers other than an oil cooler in front of the rad. The car ran comfortably cool the entire day.