I have a 17" puller fan with a shroud so that is as much fan as can be installed on a 22" X 18" radiator. Given the radiator only holds 2 1/2 gallons, I would question if speeding up or slowing down the flow with a different pump would help; hence a larger radiator? When I pull the radiator cap with the engine idling, there appears to be a good flow?
Yeah, 17" is as big as one can do on those 22"x 18" radiators. I've looked at them, or the option of placing two smaller ones on if one can optimize the surface area covered beyond the PI*(8.5")^2 from the 17. Now, do you run that fan full time, or use a thermostat for the duty cycle? I use both for my pusher, trying to minimize run-time, and do fairly well at that. I happily concede a single puller with a shroud IS THE optimal arrangement for a pure electric cooling fan system, and plan to move to some such arrangement, perhaps as early as next spring, IFF I can get the $$ for a NEW copper radiator to replace my venerable Mopar 2524984s. That would be the time for such an investment, as I then (God-willing) won't have to muck about with radiators beyond seasonal flushing and filling.
You CAN get an accurate estimate of the flow rate from your pump(s) if you have the the right equipment for it. I do. I would use a wash machine motor, belted to the pump pulley and bracketed down temporarily, fill the radiator and cooling system with water (having purged it previously) and, first sans thermostat, have a catch bucket to receive the water, run the pump until it drains the system enough to run it dry, stop, and time it. THIS will give you a good baseline for the pump's capacity in situ on your engine. You will need to know in advance the angular speed of the AC motor you use to drive the pump for such an experiment, usually something like 1500, 1800, 3000 or 3600 rpm, given their design, the diameters of the drive pulley on your test motor, and of course the pump/fan pulley.
You can then repeat your measurements with the thermostat in place, and use both colt and hot water to fill the system to see how well the thermostat regulates flow rate.
While such an experiment would likely take a good afternoon or weekend, the data might be well worthwhile.
A 26" wide radiator certainly provides greater surface area to cool those tubes, cheaply, which is exactly why Ma Par resorted to it! Despite all the grunting about how MoPar made everything perfect the first time, little details such as making the 26" x 18" radiator for the 1966 line demonstrates the fallacy in such sentiment. I love Old Mopar for their INNOVATIONS and the relative ease of working on them, and yes, CHANGING THEM when necessary.
Flow TOO FAST, and fluid media develop void spaces. Thus cavitation, an engine DESTROYING PHENOMENON! With such as the ABSOLUTE upper bound on flow rates, we now can consider heat transfer, proper thermodynamic issues. Some of this involves what materials the radiator and even the cylinder heads are made of. If I had an engine with modern aluminum heads, I probably would prefer an aluminum radiator to keep things as consistent. Thus, heat transfer times would be closer, so one could aim for closer flow rates. Conversely, with iron heads, a copper radiator will have far closer thermodynamic constants. This stuff MATTERS, to mechanical, material science and thermodynamic engineers, which, alas, I'm NOT. (I'm just an EE.)
The lower bound for desirable flow rates will be when heat STOPS MOVING. How long does it take a given volume of coolant to change temperature? One gram of water requires 4.186 joules to rise one degree Celsius. One Watt is One joule/second. So, to heat one gram of (liquid) water one degree Celsius, we need 4.186 Watts! Put another way, One gram of water will REMOVE 4.186 Watts of waste heat from a given system. Now, water has a mass density of 1 g/ml, or 1 oz weight/1 oz volume! "A pint's a pound the world around!" as it was once said. Handy, huh?
Now, 1 hp = 745.7 W. So, you can get a handle on how much thermal energy flows from you engine. Then, set an upper bound for desirable temperature. Start there, figure out what temperature change you desire from your cooling system, and estimate the temperature of the radiator environment. That will be your "heat sink." Proceed from the source, your engine, to the sink, with the power your engine produces, and figure out how much coolant it will take to remove the heat at the temperature in your radiator! Then, you can estimate the optimum FLOW RATE!!!
I can do all this good **** for you, but since this is hardly new stuff, you can likely find calculators online. All I have done is explained a wee bit how to think about the problem.
Also, allow for the fact that so long as there is no cavitation, you might get away with treating your coolant as a static substance, simply absorbing heat and magically whisking away to the radiator.
BUT, since you raised the VERY EXCELLENT QUESTION of coolant flow rate, I wanted to spell out a few things to clarify your thinking. I know from my own experience that the older MoPar non-AC pumps with their larger impellers do better with my 1965 383, which I removed the dealer AC from the first day I got it home. I ran a Gates pump from Rock Auto the first year, which did alright, but went to the more proper pump I now use 3 or 4 summers ago, and saw better results. You will have to try what suits your system best. Having now 3 little DNA copies to feed and clothe around here gets in the way of my purer experimental inquiries, alas and woe, though I might yet train them for the next decade......
Stay COOL in the meantime.
