This makes no sense on a properly shrouded car. What exactly would the fans be accomplishing?

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?

In my personal experience, this is not the case for on-track WOT situations. I have the FM Crossflow radiator and the stage 2 airflow kit with the two big spal fans and the shroud. When both fans and the shroud were on my car, I could not keep it cool on track. In 70deg ambient temps I was seeing coolant temps of almost 230. Removed the shroud and one fan, temps became much better - 214 on an 85 degree day. The car had a stack of 4 heat exchangers at the time - intercooler, rotrex oil cooler, AC condenser, radiator.

Are most of you running the factory "splash shield" behind the radiator or ditching it? The pic above with ducting/sealing off the heat exchangers doesn't have the splash shield on. Does running it help or hinder if everything from the nose to the rad. is sealed/ducted?

Duct from the bumper mouth to the axle centerline if you can.

Street car solution for someone that doesn't want to go through the effort to duct.

On my normally aspirated track car, I retain the OEM splash shield. It's a compromise that makes car maintenance easy. The OEM splash shield is pretty effective and can be made dramatically better with some well placed foam. It's effectiveness suffers once you start stacking the heat exchangers though.

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.

Are we talking a pusher fan, which I for the life of me can't see as doing anything other than blocking incoming 75mph air, or a puller fan behind the radiator? I could see how a rear mounted fan might do some good if the radiator core is not a high flow design.

Also having trouble understanding "high pressure underhood". Are you saying the under-car aerodynamics is stalling air down there to where underhood air can't get out? If so, would a simple low spoiler stop that?

Puller fan. It's quite difficult for air to get out from underhood, really. Since airflow is all about pressure differentials, dropping the pressure underhood will only increase airflow across your heat exchangers. If you don't have a pressure differential working for you, you need to yank it across with fans. There's a reason that an extraction hood is one of the most effective things you can do to improve cooling.

Fabulous replacement 》stock engine undertray 》no stock undertray.

The stock undertray has a pair of diffusers on the bottom, so that the high speed (and therefore low pressure) air under the car can pull air out of the engine bay. Mazda put some thought into it.