Does anyone know why GM put aluminum radiators in the midyear vettes? I always thought that copper has superior heat transfer abilities.
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Re: aluminum radiators
Alan-----
In terms of simple physical properties, "copper" does have better heat transfer properties than aluminum. However, an aluminum radiator can be constructed in such a manner that, overall, the radiator will have far better cooling properties than an equivalently configured "copper" type.
In fact, for proof-positive of this all one has to do is to install a "copper" replacement radiator available to replace the 63-72 GM #3155316 aluminum radiator. These radiators, which are size-configured very similar to the original units, will not provide anywhere near the cooling capacity of the original aluminum units. In anything but the least demanding of cooling requirement circumstances, they will usually not provide adequate cooling.
Most modern cars have gone to aluminum radiators because a lot of cooling can be delivered in a small, light package. So, the 63-72 Corvettes were far ahead of their time in utilizing the benefits of aluminum radiator construction. In fact, in today's world, were it not for truck applications, old-style "copper" radiators would be an endangered species.
If you want more of the details of the benefits of aluminum radiator construction, I would suggest that you go to the DeWitt's web site at www.dewitts.com. DeWitts reproduces the original GM #3155316 aluminum radiators and some excellent technical information can be found on their site.In Appreciation of John Hinckley -
Re: aluminum radiators
Hi Joe:
Why then did they install copper in AC cars like my 427 / 400? You would think these cars would require the most efficient cooling of all.
jerryComment
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Re: aluminum radiators
Jerry-----
I've wondered the same thing myself. But, I don't have a definitive answer. My guess is that the reason that most automatic trans and A/C cars built from 68+ used "copper" radiators had something to do with the need for integral oil coolers for the former and the configuration of adjacent condensors for the latter. I can tell you this, though: the highest capacity radiator ever installed in a Corvette was the GM #3007436 HD aluminum radiator used in 1965 L-78, 1967-69 L-88, 1970-72 ZR-1, and 1971 ZR-2.In Appreciation of John HinckleyComment
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Re: aluminum radiators
I believe that the Big block copper/brass radiators are approx. 45 sq.inches larger in surface area than the alum. ones. The copper/brass units are much cheaper to buy than the alum. Maybe GM thought they could get the same cooling with the larger copper radiators and save alot of cost.Comment
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Re: aluminum radiators
HEAT TRANSFER, everyone's favorite topic! At 175 degrees F, copper has 3.7 times the thermal conductivity of aluminum. The only reasons GM would have used aluminum in place of copper is 1) price 2) weight. When I went looking for a radiator for my truck, the options were a 3-row aluminum or a 2-row copper. Price was about the same, and the quoted cooling capacities were very close (i.e. it takes a whole extra row of aluminum to cool equivalently to copper). Longevity is the reason to go to copper. Also, most of the big block cars of the late 60's used copper radiators, except for those specific "exotics" that Joe mentioned. This includes 390/425 HP '66's, 390/400/435 HP 67's, 68's, and 69's. To get equivalent cooling with aluminum, you have to go bigger, either in frontal area, or depth (rows), or both.Comment
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My favorite subject -- heat transfer/field theory!
Ah, brings back the 'good ole days' of last summer before the Sun Valley trek, eh! Joe Lucia hit the nail on the head sending poster to DeWitt's web site for bone up education. Issues are:
(1) Native heat transfer of copper/brass IS superior to aluminum. (2) Thermal and electrical conductivity co-vary directly. Remember
when copper was scarce in the mid-70's and builders were putting
aluminum wiring in new homes and folks were SCREAMING? (3) Drawback to copper/brass is its low tensile strength. Given a
FIXED geometry silhouette, copper/brass hits its strength limits
WELL before aluminum when you try to make cooling tubes small
(wall thickness to ID/OD characteristics) and PACK the tubes with
heat transfer fins. (4) When you go to the limits of cooling tube wall thickness, the
'inferior' thermal conductivity of aluminum can meet and surpass
copper/brass for GROSS BTU conduction simply because you can scale
it far beyond the strength/geometry limits of 'superior' copper/brass. (5) Now, when the gross packing density of an aluminum radiator hits
it's 'rails' and you need more gross heat transfer (BB, AT, A/C
application) than the radiator can deliver in THAT SILHOUETTE, you
gotta scale up (make rad bigger). (6) When you bite this bullet, you start to stare REAL HARD at gross cost. (7) In a truly high performance environment where cost is not a primary
consideration (396, L88 both of which barred AT and A/C, mostly), OK
go with aluminum and get the weight reduction thrown in. (8) In a creature comfort environment (AT and A/C with BB), you're not
talking pushing performance limits, so why dump the $$$ to tool up
a monster aluminum radiator? (9) In real competition environments (+800 HP race silhouette), copper/brass
big radiators go 'bye bye' and nose bleed expensive (yet small & light)
off-the-shelf and full custom Griffin aluminum radiators stealth their
way out of the closet.
All this is a long winded way of saying both Joe and Everett are correct. There's a teeter totter of price/performance that's wrapped into a weight and geometry setting. PLUS, geometry rules despite Textbook of Chemistry and Physics simple thermal conductivity table lookups on material....Comment
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What Did He Say? !!! *&^%$
Brings back the old days doesn't it Jack? And, I didn't just do a table lookup - I had to convert from Kelvin to F, and from calories to BTU, and most importantly of all, I had to do it at the temperature of interest b/c the relative conductivity of al vs cu varies with temperature. And, I did bring geometry/structure into it by mentioning frontal area and depth. Bottom line is that when shopping for a radiator today, the aluminum core with plastic tanks of today are listed as the light duty application and the copper throughout are the HD applications. The L88 and 396 got the best of both worlds, adequate cooling (even though they used aluminum) AND less weight. Hey, we're all just having fun here; sometimes the geeks among us do like to go off on tangents... (not calling anyone a geek but myself!)Comment
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Re: What Did He Say? He said..........
....reduced flow cools better. :-) TBarr #24014Comment
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Don't Go There Tom... !
Even this new web site may not have enough capacity if we start up the heat transfer debates of yesteryear !Comment
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High Flow Proponent
Tom, I thought we established more air and more water equals more cooling. To prove it here is another test. Tie a long hose from the fire hydrant into your Big Block and drive around the block. We'll be waiting for those results :)
Jack does talk pretty. I knew there was something about the geometry and an advantage about the ability to manufacture the fins and attach the fins, but I couldn't recall it (probably because I slept in Thermo). Jack seems to have unlimited recall.Comment
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Re: High Flow Proponent
Alright, I should know enough when to throw in the towel, but you can't keep a good man down. Besides, look how good I made you guys look. (I still think it hinges on variables) :-) TBarr #24014Comment
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Re: I never thought of it but,.....
... this could be a whole new issue on the theory of heat transfer: Will a simple comment draw alot or just a little bit of heated responses? :-) TBarr #24014Comment
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Re: High Flow Proponent
You guys laugh if you want but as a big block owner who is visually challanged that is how my wife limits the lenght of my driving, she will only give me a little hose, so to speak, I am trying to get the city to move the hydrant further down the street. :)
jerryComment
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Coolant flow requirements
According to a 1992 SAE paper written on the then new LT1 engine, the basic coolant flow rate was determined by heater core flow requirements for cold weather operation. The implication here is that higher than necessary flow occurs at higher revs, at least on this engine. Assuming this requirement is a written or unwritten GM design standard, all of our engines may have greater than necessary coolant flow. The downside is that this will cause more parasitic drag and the possiblity of cavitation at very high revs, which can cause some potentially damaging pressure gradients in the cooling system and inadequate coolant flow. What all this means is that a low flow impeller or underdrive pulley is probably a good bet.
DukeComment
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