General rad fan question for my 56

[samdjr74]

Hi All,

I need to get a fan for my radiator. I'm running a 350 pushing around 400hp, a 700R4 behind it and the radiator is a 4 core aluminum with the trans cooler built in. My question is, is there a rule of thumb on how many CFM's my fan should be pulling per HP or displacement? I don't have A/C in the truck now but I might sometime down the road. The issue I'm running into is the space between the pulley and the radiator is very tight, a little over 3" so I'm limited to what I can do. I found 1 dual electric puller but it's only 1600CFM's and I'm a little worried that it might no be enough. Any help would be great.

Thanks,
Sam