On Keeping One's Cool
I am frequently asked about radiators; as to size, as well as what is better aluminum or copper?
Since all radiators have the same tanks (well there are two different style of tanks, those with a transmission cooler, and those without, if you have a manual trans) you do not measure the tanks. The radiator is sized only by the actual core. So it makes no difference in cooling if it is a cross flow or a down flow radiator; the core size is roughly the same for all Impalas from 1958 through 1999 at 17-1/2 inches by 25-1/2 inches. The difference in cooling capacity for the six or V-8 is dependant upon the number of cores (the thickness of the radiator).
Being a little more specific on my research these are the maximum core sizes offered by radiator manufactures starting with the 348 engine option in 1958 through the 454 in later years.
1958-'64 Down Flow Radiator Core Size 17-3/8" x 25-1/2"
(With a notched bottom tank required to clear steering)
1965-'70 Down Flow Radiator Core Size 17-1/2" x 25-1/2"
1971-'76 Cross Flow Radiator Core Size 17" x 28-3/8"
1977-'99 Cross Flow Radiator Core Size 17-1/4" x 20-5/8"
Radiators are actually sized the same way your air conditioner is at home, in terms of BTU's. Since one third of the engine's rated capacity is shed as heat, there are three different size radiators based upon the horse power ratings of the engine.
There are also very restrictive choices required by how the radiator mounts onto the core support. Prior to 1971 they all bolted in place and had to have provisions on the radiator mount to also hold in place the fan shroud. With the introduction of the cross-flow they were sandwiched between a fixed bottom plate and a bolt on top plate that made installation a snap.
There are also differences in the number of cores based upon extra heat loads placed upon the system such as living in a hot climate or behind another heat source such as air conditioning that pre heats the ambient air temperature up before the radiator sees it.
This is why the factory offered HD cooling as an option (RPO V01). This option was included automatically if you ordered air conditioning, or strongly recommended if you had a high horsepower car engine. You could order HD cooling as an option even for an under powered six cylinder if you lived in a hot climate like the desert southwest (Death Valley for example).
You really wouldn't want to be stranded by an over heated car there, so car buyers who lived there learned early on to order the HD cooling option when they bought their cars from the dealership. The HD cooling option added extra cores to make the radiator core thicker to shed more heat to the air passing through it. This option also had a radiator with a higher fin count per inch if you had an oil cooler for an automatic transmission installed in the radiator tank.
So in conclusion the biggest (which in terms of radiators is best one to buy) is a BBC radiator, with air conditioning, that also had an automatic transmission. The outlet neck is different on a BBC (straight instead of bent at a 45 degree angle), but you can use a BBC radiator upper hose (it has a 45 degree bend in the hose) on a SBC and it fits perfectly. So if you buy the BBC radiator expect to replace the upper hose (I would swap out both for new ones). Which takes care of the size question.
Aluminum or copper?
Copper cools better than aluminum because it conducts heat and electricity better than aluminum. Where aluminum shines, is in it's strength of construction. Aluminum radiators are welded together, not brazed together with a lead based solder the way a copper radiator is. Copper is so soft it has to alloyed with tin to make yellow brass. Because you have different metals you can not weld it together, it has to be soldered and the metal they use is softer and weaker than the base copper. this is why most radiators fail. The soldered joint leaks due to work hardening the soft solder. Aluminum is also much cheaper than copper which is why all of the manufactures have gone to an aluminum core radiator with plastic tanks glued on. They claim aluminum is lighter and saves fuel (that is a true statement), but the real reason is to save money.
Because aluminum is so much stronger than copper you can raise the pressure in the radiator by changing the spring in the radiator cap. This higher pressure allows the coolant to run hotter without boiling which prevents detonation in the motor. When you have the coolant boiling steam doesn't conduct the heat out of the engine so you get hot spots that allows detonation to occur. This is a good thing with modern unleaded fuel that has no octane rating compared to what was burned when these old muscle cars where new.
The only fly in the ointment is your heater core is still a brass copper soldered assembly and it will blow apart if you run a higher pressure cap. So you have to replace both the heater core and the radiator to run a higher pressure which is what modern cars and trucks have done. If any one can find a late model aluminum heater core out of any modern car that will fit in our heater boxes let me know by posting here. that way we can upgrade both and keep our cars safer from detonation.