Water flowing through the rad too quickly to remove heat when the thermostat is removed is one of those old wives tales and kinda the opposite of what really happens... reduce flow rates and coolant stays in the rad for longer, outlet temp drops which messes up the efficiency of the radiator as it's temp is now closer to that of the ambient air. Same thing with coolant inlet temp, the higher it is the better the radiator will work
What happens without a thermostat is the coolant pressure in the engine drops (unless a restirctor is fitted in place of the thermostat) which lowers the vapour temp of the coolant leading to hot spots and eventually localised boiling. Meanwhile the coolant that makes it to the rad is typically cooler than it would be with a thermostat...
The rad cap raises the pressure of the cooling system to prevent boiling when idling/from heat soak after switching off a hot engine
Piero, water capacity of the two rads doesn't really matter as tank sizes can vary a chunk. Core size is what matters with frontal area being more important i.e. if two cores have the same volume but one is thinner and longer/wider the longer/wider one will work better. As your Spitfire rad is bigger than the Strada rad you should be golden. Personally i'd fit it 'as is' using adaptors if the inlets/outlets are in about the right place and get the thing running first
What happens without a thermostat is the coolant pressure in the engine drops (unless a restirctor is fitted in place of the thermostat) which lowers the vapour temp of the coolant leading to hot spots and eventually localised boiling. Meanwhile the coolant that makes it to the rad is typically cooler than it would be with a thermostat...
The rad cap raises the pressure of the cooling system to prevent boiling when idling/from heat soak after switching off a hot engine
Piero, water capacity of the two rads doesn't really matter as tank sizes can vary a chunk. Core size is what matters with frontal area being more important i.e. if two cores have the same volume but one is thinner and longer/wider the longer/wider one will work better. As your Spitfire rad is bigger than the Strada rad you should be golden. Personally i'd fit it 'as is' using adaptors if the inlets/outlets are in about the right place and get the thing running first