The radiator is taller and and 8mm thicker than the 735I rad so larger surface area and greater capacity.
I'm eager to see how the larger radiator goes, but I'm not sure you'll have enough 'efficient' air flow to make the most of the bigger surface area and thicker core without some crafty ducting and intercooler placement in an already cramped space.
The thicker core will mean your air flow will decrease through the radiator. Increase the depth, increase the friction and decrease the air flow. If you have an intercooler in front of it, it's going to be even worse.
Because of the large frontal surface area of our 1600's (they are a hell of a lot larger than the surface area of a BMW 735 or S14 silvia), the amount of air entering the engine bay is pretty decent and getting this large quantity of now potentially hot air out is difficult. The system needs to be designed correctly to flow the air correctly for cooling and provide the pressure drop from the front of the car to the engine bay. Then channel this air out of the engine bay to the surroundings. This I think is the cause of cooling issues.
The gap that is around the intercooler in my car has been ducted to pass all air through the radiator and not spill around the sides of the radiator. I have also sealed the top of the bonnet off to prevent the air from passing underneath and pressurising/'choking' the flow through the radiator. This provides greater pressure differential and allows the all important flow from the front of the car through the radiator into the engine bay.
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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
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