Bulletproof cooling system tips

Use a radiator of at least the same square inch area that was used originally to cool the engine from the factory. The engine, not the car.
Use a radiator with the same or more radiator cores that were used originally to cool the engine from the factory. Three cores will cool most motors, although in special towing cases or applications where the motor is put under considerable load for periods of time, a four core unit may be a better choice. (confirm and expand). Once again, the engine, not the car.
In most cases, use a radiator of copper and brass construction (confirm and expand). If using an aluminum radiator, install a sacrificial anode in the coolant water.
Oftentimes, the cheapest and most bulletproof way is to use the largest radiator that will fit, along with the shroud that was designed for the radiator from the factory and the designated steel fan and viscous drive assembly for same. (confirm and expand)
Block all air passageways where the air could get around instead of through the radiator core at the front of the vehicle.
Use a full shroud with the radiator positioned so that the fan blades are half-in and half-out of the shroud hole (confirm and expand), and no more than 1" of clearance between the shroud and the fan blade tips. (Just enough to prevent intervention when the motor rocks on its rubber mounts).
Fan recommendations: OEM 18 inch, 7-blade steel fan with 2" to 2 3/4" pitch. Pitch of a fan can be measured by laying the fan down on a flat surface and measuring from the flat surface to the edge of the fan blade. Fans that are relatively flat such as a flex fan won't move enough air at idle and low engine rpm's to do the job properly.
Thermostatically controlled fan clutch.
Water pump and crankshaft pulleys sized according to what was on the engine from the factory. On a street motor, shoot for 1.2 to 1.3 times crank speed for pump pulley speed. (confirm)
Use a 180 degree thermostat. (confirm and expand) The sensor pill goes toward the motor.
Use a spiral-wound spring in the bottom radiator hose, to prevent collapse of the hose.
Use the proper pressure cap for the radiator being used.
Large engines can be perfectly cooled at very hot desert temperatures, without the use of electric fans, aluminum radiators, or various gimmicky cooling devices. (confirm and expand)
Ensure that there are sufficient openings in the engine compartment to allow the exit of all the air drawn into the compartment. This might require the removal or surgery of inner fender panels or using spacers to raise the hood of the car up an inch or two at the back.
Maintain the proper coolant/water mix to prevent freezing up in winter. Water transfers heat better than coolant, but some coolant must be used to prevent freezing.
Although it may not be necessary, the concept of a "water pump conversion disc" is intriguing. Flow Kooler originally marketed flat aluminum discs to rivet to the backside of the stamped steel impeller in the pump. With an iron impeller, a steel disc could be welded or brazed onto the impeller. The disc wouldn't be that difficult to fab up yourself. Space the water pump backing plate back farther with a couple of gaskets to prevent interference of the rivet heads on the backing plate if riveting a disc to a stamped steel impeller. More info: brazing cast iron, Flow Kooler water pump conversion discs. This disc should make an appreciable difference in the flow of water at engine speeds under 3,000 RPMs.
400 small block chevys are a special case. The cylinder barrels are siamezed in the block so that no cooling water can pass between them. This creates hot spots or "steam pockets" in the block at lower engine rpm's which conceivably could create a spot at the top of the cylinder that is hot enough to create pre-ignition. As rpm's increase, there is enough turbulence in the cooling system to wash these steam pockets away. GM engineers cured the problem by drilling holes into the cylinder heads to relieve this pressure and allow water to flow from the block up into the heads. That's all fine and dandy if you are using a 400 head on a 400 block because the heads are drilled. But, when using any other kind of head on the 400 block, there are usually no steam holes in the heads unless you are buying new heads and specify to the manufacturer of the heads that you want steam holes drilled into them before delivery. Alternately, if you already have the heads, you can have your machine shop drill the holes or you can drill them yourself if you have proper equipment.

 Swapping a core support and matching radiator into a recipient vehicle
In doing this swap, you will have to re-install the recipient vehicle's hood latch onto the donor core support in the proper location. Make up a fixture beforehand from scrap metal that bolts to the fender bolts or some other location that will be the same after the core support swap, and will show the proper location for the latch. This is a must-do when doing a frame or clip swap.

Recommended donor vehicles
'76 Cadillac Fleetwood or Eldorado. For example: 1976 Cadillac Fleetwood 8.2 liter V8 radiator.
Mid-70's Chevrolet truck with a 454. For example: 1975 Chevrolet C20 Pickup - 7.4 liter V8 radiator, 4-row capacity upgrade (and, same radiator in aluminum: here).
Cadillac radiator swap
Any of the Fleetwoods or Eldorados from '70 to '76 with a 472 or 500 will work, but the '76's used the 500 inch motor for sure.

Call around and find a boneyard that still has the fan, shroud and core support. You'll be using a new radiator and viscous drive fan clutch to bulletproof your installation. Make yourself a memo of the exact year and model the pieces came from so you can match up the parts.

You may or may not have to alter the fan clutch hub where it bolts to the water pump/pulley. Usually, the holes are slotted so you can make it work. If not, some minor surgery on the hub with a rat-tail file will do the trick. With the motor in the vehicle and finalized for position, bolt the fan clutch and fan to the water pump. Mount the Cadillac radiator and shroud to the Cadillac core support.

The Cadillac core support will probably be longer side to side than the stock one in the recipient vehicle. Retain the outer pieces of the recipient vehicle support where it bolts into the body and cut the middle part of the recipient vehicle support out with a reciprocating saw, leaving a few inches on each side. Then, measure the opening between the two stubs that are still bolted to the recipient vehicle and cut the Cadillac support to fit into this opening. It's better to leave a little more sheet metal on the Cadillac support until you determine the correct position of the fan where it engages the shroud opening. Then, position the Cadillac support with radiator and shroud attached up to the fan, equalizing the distance between the fan blade tips and the inner circumference of the shroud all around. Move the shroud around the fan until you have the fan blades halfway in and halfway out of the shroud opening. Normally, you'll have to tilt the top of the radiator/shroud back a little at the top to match the fan angle because the motor sits in the recipient vehicle on a rearward tilt. If you need a little more front to rear clearance for mounting the support, you can position the fan blades 2/3 in and 1/3 out of the shroud opening. A little further in is OK, as long as the fan clutch is at least 1" from the radiator core material. A little further out is not OK.

With that accomplished, simply attach the middle piece of the Cadillac support to the stubs of the recipient vehicle support. Use whatever pieces of sheet metal or whatever that you have to in order to make the connection. The Cadillac support may end up sitting forward of the stubs or a little behind them or it might fall exactly into place and you'll have very little welding to do to stitch the Cad support and the stubs together. Whatever. Just use your head and figure out how to connect the sheet metal, then MIG it in place.

Now, you will have a radiator that will cool anything and you still have the stock attachment of the stubs to the recipient vehicle so you can use simple hand tools to disassemble the whole mess later if you have to. It'll all come out as one piece -- because it is one piece.

Serpentine cross-flow radiators
Most cars from 1960 and up used cross flow radiators. One of the reasons was a lower stance of the overall automobile, two, the vehicles were getting wider and more cooling area was required to cool the larger engines. Cross flow rads had a tank with an inlet/outlet placed on either side. The water entered on one side and passed through the core of the rad, was cooled by the air flow and the heat escaped through convection to the outside air. Engineers found that the longer the liquid was exposed to the cooling flow of air through the rad core, more heat could be extracted from the flowing water. They slowed down the water travel by increasing the size of the water pump pulleys, but that had its limitations. They also added more rows of core, but that too had limitations. Road course racers in 1969, found a way to keep cooling to a simple easy form. To do this, they pulled the tanks off the rads that they were using and placed baffle plates in the tank covers. The baffles were placed so as to divide the rad core section into three distinct areas. Water would enter the upper rad inlet on the right side and would flow across the top section of the rad to the left side, a baffle plate located 2/3rds of the way down the tank caused the coolant to flow across the rad to the right side to the right rad tank. The coolant, couldn't rise upwards because a baffle plate located a 1/3rd of the way down stopped it and forced it to head down lower in the right tank, where it again was drawn across the rad core to the lower left tank outlet and out to the engine. This serpentine course that the coolant took, allowed the coolant to be cooled THREE TIMES by the cooling air flow coming through the core area. Excellent idea!, you say, why don't they do that to all cars today? In a closed course atmosphere, the theory works, but in real everyday life the average auto would never warm up to operating temperature during the daily commute. That's why ONLY HOT RODDERS are privileged to use this system.

ok here is a bad drawing but you get my drift

DOES TUBE SIZE MATTER??

The purpose of the radiator is to get the engine up to operating temperature as quick as possible, help it maintain optimum temperature, and remove excess heat when required. The radiator is another name for a heat exchanger, whereby combustion temperatures up to 4500 degrees are transfered to the cooling system of the engine block and taken outside the block via flexible rad hoses to be exposed to the cooling force of air through the rad core, thus, reducing the temperature of the coolant before returning it to the engine block. There are two restrictions in the system. One is the thermostat, which restricts flow and holds heat in the engine until warmed up, and the other is the rad core tubes. The rad tubes have to be of sufficient size so as to allow the coolant to flow through in an unrestricted manner, but also able to 'scrub off' BTU's or heat; which is based on the shape of the tube and the convection of heat away from the coolant to the outside air. A wide flat tube will expose more surface to the outside flow of air that a narrow tube . The reason for this is more surface area is exposed to cooling. Look at the pictures located below and see why that is.