Doug is right about this, and Ross I'm kind of surprised to hear that you push those fans. Fixed fans cost horsepower, even the cheaper flex fans take 10HP or so to run at high engine speeds. I'll bet those fans you like take more. A good electric fan (Spal) will cool better at idle speeds than any fixed fan because they are running at full speed, and of course they don't cost anywhere near as much power. The problem that people get into with electric fans, IMO, is that they buy the cheap ones. Those just don't work very well; for example the Flex-a-lite Black Magic fans are junk, based on my own experience. They put out these ridiculously high cfm numbers in their advertising but when it comes to pulling air through an obstruction, like a thick radiator, they just don't work.
Recipe for effective cooling in a big engine, small engine compartment vehicle: 31" X 19" two core aluminum radiator with 1" or 1-1/4" cores, two Spal puller fans that are as large as you can fit (12" diameter minimum), no fan shroud, 180 degree thermostat, and four 1/8" holes drilled in the thermostat if there's no water pump bypass. This has worked for me on my 1000 HP SOHC Shelby clone, in my Mach 1 when I had the 1200 HP supercharged FE installed, also the Mach 1 with the 850 HP high riser installed, and in both my Galaxie SOHC installations. Works every time.
So, first to qualify my statement, my point is moving a ton of air with a fixed fan is easy, because you can go as aggressive of a pitch, as big as you can fit, and adjust pulley speed because you have plenty of power. I wasn't inferring that somehow horsewpower = airflow. I apologize for the brevity
Second, remember what I build and where I come from, experiences in the desert and southern states as a guy that moved every 3 years for about 20 years shaped me since the days living up north. When in the northeast, I could almost take a fan off an engine and run it around town, same in 50% of Nebraska seasons, although summer is tough. I also thought guys who couldn't keep things cool had some basic understanding problem
However, when stationed in Vegas, Alabama, and even to some lesser extent in Virginia, usually in stagnant tunnel traffic, I found that those fans worked so well (assuming you had a good pulley combination for the right shaft speed) that the cost on the street was worth the power. In other words, it stayed so cool, so easily, in so many situations, that it would easily be worth the 10 hp to me and I likely could tune more aggressively with a more stable platform.
I would also argue, that a 10 hp dyno test on a fan is likely accurate as a static test, may not be accurate when you have airflow at speed. Assuming you don't need the fan because the airflow is adequate, then the fan likely isn't pulling as much, the pitch will create a speed and it's not going to be additive. I'd love to see the trap speeds on a consistent car and see how it changes.
Of course, I won't argue that the same car can cool between rounds with an electric fan, can't do that with a fixed fan
Now, if trying to sneak every bit of HP out, I agree, but then, that means you might have to accept some other behavior. A shock tower car has an exit airflow problem IMHO, and especially if no hood scoop or other way to relieve the exit air.
I also agree with your success Jay, but, first it is "a recipe" not "the only recipe" but of your list, the only thing that would fit in a car like mine (shock tower FE car, battery up front) would be the drilled thermostat, which really doesn't apply at temp anyway. So it's hard to compare your results, although I assume your Mach is still a shock tower car, but I would also assume you have a bit more room with your electric water pump, although I won't throw stones at your setup or anyone elses if it stays cool. All I can say to the crowd is trust me things aren't the same throughout the US, you'd likely find Jesus if you were temps that blister your hand if you leave a screwdriver outside and grab it or burn skin if you kneel on asphalt (which is often melted at that point). My Mustang and about 6 tri-5 Chebbies from 400-600 hp, and a bunch of 385 series builds in Vegas will idle happily in traffic that way. Now truth be told, we did a 600-ish HP 55 Chevy, and it used dual Spals and a huge radiator (in fact almost exactly your combo except we ran a restrictor not a thermostat back then) and did fine, but we also had to push the radiator forward and build a custom support to fit something like you designed
Last comment, as you pointed out, I agree COMPLETELY that the only non-OEM fan I think could be worth anything using their advertised ratings would be a properly sized Spal, but even then, as you point out it really needs to be a system, not just slipping a fan on the front of the radiator. All the other aftermarket versions are over-rated and I haven't found an electric fan worth a shit that works on a 24 inch Mustang radiator and gives room for the water pump
Sorry for the long winded response, but remember, 40 bucks and 4 bolts over most flex fan Certainly other ways to fix it, and other ways to save HP, but I have found it to be a valid fix if someone wants to make a change, especially on a budget or timeline
