How much better does a flat tube radiator vs round tube radiator cool? It is a 1911 Torpedo
I'm not sure that there's a definitive answer to your question, except to say, better. I think either one will work fine for you, given it's a new radiator. Never heard anyone state that their new round tube radiator wouldn't do the job. (Assuming the car has no other issues.)
I've never used a flat tube radiator, but based on what I've heard and seen, they do a better job. From a practical point of view, in mild weather cruising on a flat road you probably won't see much difference. In 105 deg. F. heat doing stop and crawl in a parade the flat tube is going to do a better job.
I needed to replace the radiator on my '24 coupe as it was leaking badly and was deemed beyond repair. (The radiator repair shop had phoned to say "I'm sorry Mr. Harper, but this is no longer a radiator, it's a lawn sprinkler".)
So, after receiving advice and counsel, I purchased a flat tube radiator from Brassworks.
I felt that it cooled too well. Now, I do realize that statement must sound crazy to most or many T drivers. I have a Motometer on the car which I have checked and it seems to be reasonably accurate. I had also cleaned the block's water jacket very well. When running I would not see the red indicator on the Motometer. I tried partially covering the radiator to see what would happen. The red would appear.
I installed a thermostat and would then observe the red indication a bit below the circle on the dial. We do have hills here in New Hampshire and the coupe does not boil over. Yes, the engine temp will rise if on a long steep climb and on a really hot day, but it soon drops back to normal. The cooling system is doing what it is supposed to do.
All combustion engines must reach Normal Operating Temperature [NOT] in order to operate efficiently. A cold engine wastes fuel and does not develop full power if it never reaches NOT.
If I had to again replace the coupe's radiator I would give serious thought to a round tube. Now, a brass car with it's smaller radiator, well, possibly the flat tube is worthy of consideration. My two cents worth, perhaps over valued. Bill
If I had an '11 Torpedo I would go for the round tube radiator because it is correct for the car. I have one on my '10 in Florida and often find myself sitting at a draw bridge in 95 degree weather for 10 minutes and it doesn't overheat. I might add that the radiator is now well over 20 years old. I went for the flat tube on my driver but did it more for the price than for the cooling performance. I think it is a a misconception that the smaller brass radiators do not cool well enough. I think it is based on so many old ones out there that can no longer cool effectively because the tubes no longer make sufficient contact with the fins to dissipate the heat.
Val's observation about contact between the tubes and the fins is correct and critical. A round tube radiator should work just fine in all but the worst conditions if the cooling system is clean and the tubes have good contact.