Common consensus seems to be a minimum of 2200-2500cfm for an electric fan to be suitable for replacing the mechanical fan.
Most people who do the electric conversion don't note this, or hold to it, and end up reversing the conversion later.
There's nothing making the job actually impossible, but you will run into a slight barrier between fan size and consistent output - mainly due to the low height of the radiator core.
If I were really hitting my head on cooling, I'd want to do this:
Add volume to the cooling system. A pressure cannister somewhere that holds an extra gallon or so of coolant will significantly increase the "heat removal capability" of the system - even if the radiator area isn't increased.
Engine oil cooler. The engine oil is closer to the point sources of heat than the coolant - and the extra oil volume also increases the ability of the system to transfer heat. Adding capacity to the circulated oil (just like the circulated coolant) is helpful, but the addition of an effective oil cooler will do that while giving the oil direct cooling.
For exotic engines (high forced induction, exotic fuels with high heat values,) the addition of "oil piston cooling" is valuable - but also a lot of work. In this case, small spray jets are added to the system to constantly spray the underside of the piston with engine oil. The addition of an engine oil cooler with the piston cooling is more than a good idea - it is damn near mandatory. This is the sort of thing that has to be done while an engine is torn to bits - but it can be a valuable mod to the right engines.
Other things that prove useful:
Addition of a radiator with an extra core, or with "high heat transfer" capability (like a Modine or Performance Parts "Desert Cooler" radiator.) This will give more effective heat transfer area, and therefore the ability to eject more heat. This is complemented well by the addition of a "high volume" water pump, which allows more coolant to be flowed through the radiator
Water Wetter. An additive by RedLine, WW lowers the surface tension of water, which allows for more effective contact between the cooling fluid and the system heat exchangers (the engine surfaces and the radiator.)
If you're looking to increase the cooling capacity of the system, you have to look at the entire engine and support parts as a system, then address apparent deficiecies that are not accounted for elsewhere in the whole package - that's the trick.
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