Mr. Mike, I donít think I ever wrote to you before. I tend to write novels if I get the slightest bit of encouragement. You are pushing that button. I will try to keep out of the weeds on this thread.
To select a fan, you need to know four things.
1. The desired flow rate measured in CFM.
2. The static pressure of the system measured in inches of water (SP).
3. The air density.
4. The type of fan.
1. You mentioned the desired flow rate for a big block Chevy is 3000-3500 cubic feet per minute.
2. What is the static pressure of your radiator? Nobody knows. This is why you are concerned if you are making the correct purchase. The manufacturer does not publish the numbers. So, you try to make an estimated judgement. Compare the little holes the air flows through with your stock radiator. Are they about the same size? If they are bigger then the static pressure will be less. Do you have a larger radiator is terms of height and width? If it is larger radiator then the static pressure will be less because it has got more little holes. How deep is the radiator? If it is thicker, then, the static pressure will be more. How much more? Who knows? So we go around in circles and never come to a conclusion.
3. I live about 20 miles outside of Houston, Texas. The altitude is 112 feet above sea level. The air is dense here. A person living in Pittsfield, Massachusetts (1000 feet above sea level) will have a radiator that will run hotter than mine.
4. An axial fan is the only type that will fit.
So how does someone pick a fan? It is almost impossible to pick too large of a fan. If you managed to pick one too big, the thermostat will regulate the temperature and not let the motor run too cold.
In the past, I use to do work cooling semiconductors on heat sinks. Blowing air across the heat sink fins makes a dramatic improvement in the transfer of heat. A gentle breeze would bring the temperature down drastically. When I blow more air, there is a point where a lot of air does not lower the temperature. The heatsink temperature hits a plateau and just stays about the same temp even though more air is blown across it. If your car is running hot, sometimes more air is not the solution. You need a bigger radiator.
The biggest factor to get the most cooling is to pick the largest fan that will fit. You picked two 11Ē fans. I donít think two, 12 inch, fans would fit on your radiator. So, the size of the fans you picked is the best option for your radiator.
The number of fan blades will affect the flow rate. More blades mean more CFM. The pitch of the fan blades matter. There is a sweet spot on fan blade pitch. The sweet spot is where the fan moves the most air with the least amount of current.
The blades can be straight or shaped like the letter S. The ďSĒ shape blade will be less noisy but not as efficient.
You picked a Be Cool fan assembly model 75007. It comes with Spal fans. This assembly looks very much like the Spal 2VA06-AP6-37A fan and shroud assembly. Here is a link to the Spal assembly.
I compared my fans to your fans. Our fans are both 11 inches in diameter. My fan has seven, S shaped, blades. Yours have five, straight blades. I think the blade pitch is greater on my fans, but I cannot be sure.
At 0 inches of water, (fan is running in free air), your fans will outperform mine. Yours will flow more air. Your fan will continue to be better up to 0.4 inches of water. The range between 0.5 to 0.9 inches of water, my fans will flow more air than yours. At one inch of water your fan is the better one.
This tells me your Be Cool radiator fans will cool better than mine as long as there is little restriction. I am stacking an AC condenser and an air to water heat exchanger in front of the radiator. I have a lot of restriction, so it is more important to me the range of 0.5 to 0.9 inches of water flows a lot of air. This is the area of the fan curve I am going to be operating.
You picked about the best fan assembly for your car. The only way you are going to get more airflow is to buy a fan with more blades. You donít have an intercooler. I am not sure you have a condenser. I really think your mild big block will stay cool and happy.