I agree, there is engineering that goes into it. If the OP is short on room two 1 inch tubes is LESS thick that your .75 3 core and it will flow more coolant at the same pressure and pump speed.
Two 1 inch tubes will cool way more that what the OP has IF he has thought out the rest of the cooling system. That means a quality high volume water pump, over drive pulleys and a decent fan. If anyone has that, two 1 inch cores will cool way more than what is claimed.
Fins per inch has its limits as well. Get too many fins per inch and you can’t get enough air through the radiator to cool anything. Too few fins and you can’t dissipate the heat quick enough.
I forgot to mention you also need a quality high flow thermostat. The only thermostat I’ve found that is always fully open by it’s rated temperature is the Robert Shaw/Stewart Components thermostats.
I just had a Pontiac guy call me on Monday and his engine runs at 192-195 a 180 thermostat. So I had him pull it out and verify when it opened. And sure enough it was starting to open at 180, when it should have been fully open by then.
A new thermostat is on the way.
There is certainly more to it than the number of cores and the size of the cores. You can run a 4 core radiator too, but what do you get? A total of 2 inches of tube. Same as a 2 core with 1 inch tubes and the two 1 inch cores will flow more coolant than the 4 cores at .5 inch each.
Fit the biggest radiator with the biggest, fewest cores you can get and use the thermostat to set your minimum operating temperature. Build in some safety margin so a few years down the road you won’t need to buy another radiator when you increase the power.
