A couple of comments about flow through the radiator. For those driving unrestored cars or older restorations, it is worth checking for a build-up of debris (bug carcasses, dirt & silt, and other junk) between the AFT face of the radiator and the protective screen. It's a bit of a forgotten area but a collection of junk here can significantly impede flow.
Perhaps more interestingly, another impedance to flow may be the screen itself. I recently fitted a new aluminum radiator, and wondered how much of a flow restriction may be created by the rather chunky screen itself. I did some math and was astonished to find that, of the window described by the border of the screen, more than half, 53%, was covered by the screen wire. Finding this hard to believe I tackled the math from another direction and came up with 57% coverage. This is an incredible number.
I Figure that considerable improvements to cooling system performance could be gained here. When I bought my radiator, the maker also offered a very lightweight, honeycomb membrane screen that provides almost no resistance to air flow. I was uncertain about using this seemingly flimsy material to protect my rad, but it is sold to dirt track racers to protect radiators, so it must be able to withstand significant abuse. I made up a new screen from this stuff and fitted it with velcro so it could be removed occasionally for cleaning. I have since emailed the company to ask what this stuff is called, and where can I get more of it, but they have not replied. Anyway, thought I'd pass this along.
