FSAE Rule of thumb: Cooling system should be able remove 1/3 of max engine power as heat.
Civics with aftermarket smaller cross-section, thicker radiators generally run type r engines (from my observations)- stock these produce more power than most mod'd mx5s. Comparing a BP’s to any k series or b series honda type r engine is a joke. Not only are they making more power, but they are making more power at a higher RPM (if you can’t see why this is significant, stop reading now).
So what is to stop a radiator that is suitable for these high powered Honda engines? What are the other key components/ factors of a system?
Fluid flow rates play an important role in the efficiency of a cooling system = water pump and fan/air flow (car speed)/air temperature (can't control the air temp)
So, what is the flow rate of a standard 5 water pump at X RPM? How does this compare to that of k or b series type r engine at X RPM?
What is the pressure drop through each radiator?
What is the pressure drop across the face (front to rear) of the radiator? Thicker core will have a higher pressure drop due to skin friction between the fins and the air. On radiator core – there are stupid amounts of differences between the fins alone. Not all radiator cores are created equal!
What is the recommended operating temperature for each engine?
There are 2 main methods to calculate the efficiency of a heat exchanger – both require much more detail than what I have listed above (for those playing at home – LMTD and eNTU).
I suggest doing some research to find out how much power the Honda engines are running with similar sized radiators and how their water pump differs in performance to that of the 5. You might find that due to the higher rev’s the Honda water pumps have a greater flow rate.