Champion radiator - I cut her open
You don't need a double pass radiator. You don't need 4 cores.
2 cores of 1 inch each will cool well over 800 HP if and this is the big IF, the water pump has the ability to keep up, and you are turning it the right speed.
2 cores of 1.25 inch would be even better.
No reason to ever use a 4 core. You need FLOW.
It's not that simple. As Charrlie_S said earlier, it's about surface area. The flow rate of water through the radiator is important as well, but the surface area exposed to the incoming air is the driving component. The surface area and the speed of the air are by far larger parts of the equation, literally.
You want the surface area of the tubes to be maximized. To do that you have to balance the dimensions of the tubes with the number of tubes you can have. Just saying the tubes should be longer only addresses a single component, and that's what is meant when it's said the tubes are 1". The tubes have width and length, and you're only addressing length, first of all. You can have 1" tubes that are as narrow as the top picture. The smaller the width, the more water will be exposed to the surface of the tube, which is good to a point. But as was already mentioned, if the tubes are too narrow it will restrict flow and they'll be prone to plugging up. So it's a balance, you want the most surface area you can get without restricting the flow too much, both new and then later when things develop some corrosion. The extra cores don't help if they're plugged.
Same thing with the number of cores. More rows of tubes=more surface area, which is a good thing. But, the problem is that the air passing through the radiator is warmed and slowed as it goes through. So, the more cores you add, the thicker the radiator gets. As the air goes through it slows and warms more, which makes the additional rows less effective and you lose efficiency.
I tend to agree that a 4 core radiator is too much, they end up being too thick and the length of the cores is usually diminished. The surface area is still higher because of the number of tubes, but the efficiency is lower. And they usually end up being thick enough that they make fan choice a problem. You want to find a good balance between the surface area of the tubes, the amount they can flow, and the size of the fan that you can run. A ton of radiator can be good, but if it compromises the fan CFM then you've gone too far.
I really like the Champion 3 core 26" radiator I run, and it still allows enough room to run a set of dual fans that will flow 3,500 and 5,000 cfm on low/high fan speeds.
