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Science behind Mopar cooling?? #2866166
12/29/20 07:28 PM
12/29/20 07:28 PM
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Montclaire Offline OP
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Hello, I have a 74 Barracuda with a transplanted 440. This is a factory non-AC car so it has a 22" radiator (newer stock-style replacement for the 1974 factory 19" unit). I'm going through the cooling system and will be replacing the water pump. As I understand it, non-AC cars got a 22" radiator, the larger pulley and an 8 blade pump. AC cars got a larger radiator, the smaller pulley and 6 blade pump. The net effect was a slightly under-driven pump on the non-AC cars and an over-driven pump with AC (around 140%).

I have both pulleys to choose from but haven't decided on a pump yet. I am not running AC, just want to cool the 440. Now, some subscribe to the theory that a faster pump is always better but I can't see how that would be accurate. The factory obviously had a reason for two different setups. My guess would be to give the coolant enough time to properly do its job with the smaller radiator. The AC cars probably got a 6 blade pump to reduce cavitation and the smaller pulley to increase pressure in the system. What did non-AC police package cars use?

Thanks in advance

Last edited by Montclaire; 12/29/20 07:35 PM.
Re: Science behind Mopar cooling?? [Re: Montclaire] #2866234
12/29/20 09:57 PM
12/29/20 09:57 PM
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Can't give you a reason why the facotory did what they did, but the more/faster the water moves through the system the more heat transfer/cooling you get. The old wives tale of water going too fast is just that, a tale.

Of course, the University of Minnesota heat transfer lab could be wrong too, but since they have been at it since 1880, probably not.

Re: Science behind Mopar cooling?? [Re: SportF] #2866238
12/29/20 10:05 PM
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Faster with wrong impeller does not mean faster water if cavitation occurs. Hard to really know what they were doing unless an engineer has the notes. Proper cooling, not too much power loss, versus AC with more power loss and heat generation at higher idle speed. I guess it all depends what you want to do with the car, but once you have sufficient cooling rate, getting more is not a benefit. Is car going to idle a lot in city driving, or cruising at higher rpm, or spend most time at high rpm doing the 1/4 mile.

Re: Science behind Mopar cooling?? [Re: dragon slayer] #2866257
12/29/20 10:46 PM
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It's running hot at lower speeds (as is steam, not just high on the gauge). I'll be adding a shroud and a 5-blade viscous fan to replace the mickey mouse flex fan that's on it now, along with new cap, thermostat, cooler plugs, checking the advance, etc. It already has an overflow tank and runs cool enough at speed so I'm assuming it's not blocked up otherwise.

I came across this thread: http://www.dodgecharger.com/forum/index.php?PHPSESSID=qdp6mreo87eglkba11hdrim0o0&topic=60599.0
There's a lot to read there but starting on page 8 there is a comparison of water pumps. Pump #1 is a motor home piece with an 8 blade impeller measuring 4.375" across that has really good flow numbers at low speed. So not only is there a difference in the number of fins, but also the diameter of the impeller, and I'm assuming the pitch of the fins determines the curve of the flow.

It looks like I am better off with an 8-blade pump so long as the impeller is big enough. NAPA makes a stock looking one. I can always speed it up with the smaller pulley I guess, which will give more flow at lower rpms. This is just a street car, it may see a bigger cam as the motor feels pretty tame right now but nothing wild. It's going to see a lot of low speed city driving under 40mph so it'll have to run a little cooler to be happy. The last owner also opened up the hood scoops which doesn't do much on the Barracuda hoods (may actually hurt) so they'll get plugged back up, too.

Last edited by Montclaire; 12/29/20 10:52 PM.
Re: Science behind Mopar cooling?? [Re: Montclaire] #2866266
12/29/20 11:14 PM
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The shroud alone will pay big dividends.
Colder spark plugs won't affect cooling, and open E 'Cuda scoops has no appreciable effect.

Re: Science behind Mopar cooling?? [Re: Montclaire] #2866267
12/29/20 11:17 PM
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For a street car the faster you can spin the water pump the better. If you start driving at high speeds then you'll have to rethink the drive ratio. The factory engineers changed the ratio for the engines that were capable of higher speeds since they were most likely worried about cavitation. For a street car I'd duplicate the HD cooling package that you could get with the tow package. I think police cars and taxi cabs also got the HD cooling package. It should be spelled out in the master parts book for your make and model.

Re: Science behind Mopar cooling?? [Re: Montclaire] #2866268
12/29/20 11:18 PM
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NAPA shows two pumps, TFW 42032 and WP 58173. The 42032 pump impeller measures 3.84", haven't found a measurement on the other one yet. The smaller 6-blade impeller probably frees up some HP on a drag car but I'm going in the other direction.

Re: Science behind Mopar cooling?? [Re: AndyF] #2866270
12/29/20 11:21 PM
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Montclaire Offline OP
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Originally Posted by AndyF
For a street car I'd duplicate the HD cooling package that you could get with the tow package.


Andy, I'd love to but it's got the narrow yoke and I'm not cutting it for a bigger rad. Chrysler built a lot of big blocks with 22" radiators so I'm sure it'll be ok if the parts are matched.

Re: Science behind Mopar cooling?? [Re: Montclaire] #2866272
12/29/20 11:36 PM
12/29/20 11:36 PM
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If you're cooling well at cruising speed but poorly at low speeds the shroud and proper fan will make a big difference. Also the rubber seal at the front of the hood so air is forced through the rad at speed.

Re: Science behind Mopar cooling?? [Re: DaytonaTurbo] #2866297
12/30/20 02:25 AM
12/30/20 02:25 AM
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I read somewhere that they used the smaller impeller pump on the A/C cars because they overcooled with the big pump at idle which was caused by the higher idle speed spec. This was likely a concern for emissions and in town fuel mileage.

Kevin

Re: Science behind Mopar cooling?? [Re: Montclaire] #2866346
12/30/20 09:24 AM
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Less vanes so less total drag when the AC compressor is on?


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Re: Science behind Mopar cooling?? [Re: A39Coronet] #2866364
12/30/20 10:16 AM
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If you're using the A/C pulleys, your fan will also spin faster than crank rpm which will help at idle and low speeds. Don't know if that's an issue for you, but wanted to mention it.

Re: Science behind Mopar cooling?? [Re: mrob] #2866409
12/30/20 11:49 AM
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There is no one answer to this I bet?

Every big block car I have ever owned always needed a 26 inch radiator!
No engine driven fan was ever good enough to ‘draw out heat’ in a traffic jam.

So it’s twin electric fans if you wannabe safe!
On the whole it will not be needed, in slow traffic one fan will suffice.
In heavy traffic both fans will deffo be needed and a good charging system to cope too.

Water pump selection is a difficult choice but an all Ali set-up, pump and housing is a must.

The pump blades must have a backing plate as this reduces cavitation and the Chevy spiral style pumps are useless... panic

Last edited by Gtxxjon; 12/30/20 11:55 AM.

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Re: Science behind Mopar cooling?? [Re: Montclaire] #2866426
12/30/20 12:28 PM
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It's running hot at lower speeds (as is steam, not just high on the gauge). runs cool enough at speed so I'm assuming it's not blocked up otherwise.
as said you need more air and or water flow. after the fan/shroud I would get the 8 blader & tack weld an anticav plate behind the vanes (cut the round piece in two & weld on each half


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Re: Science behind Mopar cooling?? [Re: Montclaire] #2866444
12/30/20 01:06 PM
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The reason for overdriving the pump was to turn the fan faster, more cooling airflow at low speeds. Turning the pump faster could cause cavitation, thus the smaller impeller.


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Re: Science behind Mopar cooling?? [Re: John_Kunkel] #2866505
12/30/20 02:46 PM
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what cavitation could one expect with a spiral [chevy style] pump impeller ?
i know this style is not widely accepted, but i am curious. especially used with a small pump pulley.
beer

Re: Science behind Mopar cooling?? [Re: moparx] #2866522
12/30/20 03:03 PM
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Chrysler used the 6 vain pumps on AC cars for this reason, remember there was an AC condenser in front of the radiator that isn't there with non AC cars. The condenser is not only restricting airflow through the radiator but it's transferring it's heat to the radiator so, Chrysler slowed the flow through the radiator to give the fluid more time to cool.


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Re: Science behind Mopar cooling?? [Re: GODSCOUNTRY340] #2866546
12/30/20 03:29 PM
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Originally Posted by GODSCOUNTRY340
Chrysler slowed the flow through the radiator to give the fluid more time to cool.


Not how that works at all. If the water spends more time in the radiator to "cool", then it also spends more time in the engine getting "hot". So, at best, it would be a wash.

The biggest factor in thermodynamics the the temperature differential not the time in the radiator.

Re: Science behind Mopar cooling?? [Re: GODSCOUNTRY340] #2866549
12/30/20 03:33 PM
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Originally Posted by GODSCOUNTRY340
Chrysler used the 6 vain pumps on AC cars for this reason, remember there was an AC condenser in front of the radiator that isn't there with non AC cars. The condenser is not only restricting airflow through the radiator but it's transferring it's heat to the radiator so, Chrysler slowed the flow through the radiator to give the fluid more time to cool.

Nope. As Kunkel stated above, it’s to increase airflow while not increasing the opportunity for cavitation.

Re: Science behind Mopar cooling?? [Re: John_Kunkel] #2866576
12/30/20 04:18 PM
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Originally Posted by John_Kunkel
The reason for overdriving the pump was to turn the fan faster, more cooling airflow at low speeds. Turning the pump faster could cause cavitation, thus the smaller impeller.


Now that makes a lot of sense. The iron pumps do not seem to need the anti-cavitation plate as they have a flat backing surface for the impeller. The aluminum pumps usually have a cavity so they would require the plate. I'll be using an iron 8-blade pump with an impeller over 4". Right now the car has the larger pulley on it. If I pull the pump and find it's an 8-blade, I'll swap to the smaller pulley with the shroud and clutch fan and see how it does.

Last edited by Montclaire; 12/30/20 04:24 PM.
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