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Air Flow across 327 300 hp Radiator

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Old 01-11-2018, 08:41 PM
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Default Air Flow across 327 300 hp Radiator

I too, like many others here have problems with overheating in stop and go traffic. Over the years I've tried many things but to no avail. Time to start taking a more objective approach. Does anyone know what the design air flow over a small block 300 hp radiator is supposed the be at idle motionless?

I ask because this is something that can be easily measured, then compared to design specs thus including or eliminating the fan or clutch.

has anyone ever measured the air flow? If so does your overheat and what kind of feet per minutes did you measure?

i have a new Dewitt's 66-124427 aluminumradiator, 50/50 antifreeze mix, etc.

hoping to gain some knowledge and insight.

Thx!
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Old 01-11-2018, 08:48 PM
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Old 01-11-2018, 10:05 PM
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Originally Posted by Nowhere Man View Post
Very good article! I've got a few other things to look into now. Nothing on an airflow specification over the face of the radiator. Hopefully someone knows or has measured AIRFLOW on theirs so I can at least compare to mine. Also, I've got no seals around the radiator but it's always been my understanding they weren't used on 66 models that didn't have AC.
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Old 01-12-2018, 07:10 AM
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Confirm the dash gauge readings first. The 67 A/C rubber seal can be used on your car with some trimming.

Doc Rebuild has the best repels.
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Old 01-12-2018, 08:46 AM
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You could try a heavy duty fan clutch and 7 blade fan. I have no problem using these and the OEM radiator with vintage air here in Florida.
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Old 01-12-2018, 09:59 AM
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I have a 7 blade fan on my 67 300 ac coupe and she runs cool all the time. I think installing the lower seals and the wide rubber one on top of the core support will help direct airflow thru the radiator.
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Old 01-12-2018, 10:02 AM
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Originally Posted by Nalrops View Post
Nothing on an airflow specification over the face of the radiator. Hopefully someone knows or has measured AIRFLOW on theirs so I can at least compare to mine.
How did you measure air flow across your radiator.

GM probably produced test data that showed CFM vs. fan speed, but I've never seen it.

Heat exchangers are usually tested with varying flow rates and temperatures of both fluids, but they can be tough to read unless you have some background in heat transfer. No doubt GM tested the OE type aluminum radiator, and if the data exists, Tom DeWitt might have it. Ask him.

If you have a relatively new DeWitts OE replacement radiator and are experiencing "overheating", which you have not defined, then the culprit is likely either the spark advance map, like a dead or incorrect VAC, or the fan clutch. Most modern replacement fan clutches are "tuned" to the typical 195F thermostat opening temperature of later emission controlled engines, so they don't tighten until a higher radiator exit air temperature, which can easily cause coolant temperature to run in the 200-210 range in hot weather low speed traffic.

Keep in mind that the normal operating temperature range of these engines is 180-230F, and with a 50/50 glycol water blend and a 15 psi cap, the coolant boiling point is 265F, so you still have over 30 degrees boilover margin at 230.

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Old 01-12-2018, 02:19 PM
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Originally Posted by Nalrops View Post
I too, like many others here have problems with overheating in stop and go traffic. Over the years I've tried many things but to no avail. Time to start taking a more objective approach. Does anyone know what the design air flow over a small block 300 hp radiator is supposed the be at idle motionless?

I ask because this is something that can be easily measured, then compared to design specs thus including or eliminating the fan or clutch.

has anyone ever measured the air flow? If so does your overheat and what kind of feet per minutes did you measure?

i have a new Dewitt's 66-124427 aluminumradiator, 50/50 antifreeze mix, etc.

hoping to gain some knowledge and insight.

Thx!
I did a search on the DeWitts website for the radiator number you gave (66-124427) and couldnít find it. So, Iím not sure what radiator you have in your car. As you probably know, original radiators installed in midyear small blocks were a stacked-plate aluminum design with a heat rejection rate of 4600 BTU/min.

The DeWitts Restoration Radiator (Model 941 for í65-í67) is also rated at 4600 BTU/min. I know of no other aftermarket radiator for midyears with this high of a heat rejection rate. So, anything less is a step backwards in cooling capacity.

As Duke said, Iíve never seen radiator air flow data either. I have seen data on things like water pump capacity (57 gal/min @ 4400 RPM) and fan clutch specs (fan speed 3200-3500 @ 4000 RPM & 135-155*F), which are almost imposible for owners to measure. Data like this is available in the Corvette Spec Books available from gmheritagecenter.com.

Since heat transfer and air flow are the two things that matter most for cooling, after eliminating previous suggestions, you might consider a Spal fan to increase airflow.
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Old 01-12-2018, 03:55 PM
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Originally Posted by Nalrops View Post
I too, like many others here have problems with overheating in stop and go traffic. Over the years I've tried many things but to no avail. Time to start taking a more objective approach. Does anyone know what the design air flow over a small block 300 hp radiator is supposed the be at idle motionless?

I ask because this is something that can be easily measured, then compared to design specs thus including or eliminating the fan or clutch.

has anyone ever measured the air flow? If so does your overheat and what kind of feet per minutes did you measure?

i have a new Dewitt's 66-124427 aluminumradiator, 50/50 antifreeze mix, etc.

hoping to gain some knowledge and insight.

Thx!
What's your timing curve like? Insufficient timing advance at idle and low RPM can cause overheating issues too.
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Old 01-12-2018, 05:41 PM
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Originally Posted by 69427 View Post
What's your timing curve like? Insufficient timing advance at idle and low RPM can cause overheating issues too.
Help me out here - to come up with a timing curve are you suggesting I plot rpm versus timing as indicated by the use of a timing light??

If so, how would I know if my curve is exacerbating the problem or if it's in line with expectations??

Thanks,
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Old 01-12-2018, 05:44 PM
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Originally Posted by Mike67nv View Post
I did a search on the DeWitts website for the radiator number you gave (66-124427) and couldnít find it. So, Iím not sure what radiator you have in your car. As you probably know, original radiators installed in midyear small blocks were a stacked-plate aluminum design with a heat rejection rate of 4600 BTU/min.

The DeWitts Restoration Radiator (Model 941 for í65-í67) is also rated at 4600 BTU/min. I know of no other aftermarket radiator for midyears with this high of a heat rejection rate. So, anything less is a step backwards in cooling capacity.

As Duke said, Iíve never seen radiator air flow data either. I have seen data on things like water pump capacity (57 gal/min @ 4400 RPM) and fan clutch specs (fan speed 3200-3500 @ 4000 RPM & 135-155*F), which are almost imposible for owners to measure. Data like this is available in the Corvette Spec Books available from gmheritagecenter.com.

Since heat transfer and air flow are the two things that matter most for cooling, after eliminating previous suggestions, you might consider a Spal fan to increase airflow.
The numbers I reported are right form the invoice. Whether the numbers I've reported is the actual models number of the radiator, I'm not sure but I am confident I have an exact match radiator form Dewitts.

I was asking about airflow data because air flow is measurable, just like temperature, or gpm, etc.........

Thanks,
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Old 01-12-2018, 05:51 PM
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Originally Posted by SWCDuke View Post
How did you measure air flow across your radiator.

GM probably produced test data that showed CFM vs. fan speed, but I've never seen it.

Heat exchangers are usually tested with varying flow rates and temperatures of both fluids, but they can be tough to read unless you have some background in heat transfer. No doubt GM tested the OE type aluminum radiator, and if the data exists, Tom DeWitt might have it. Ask him.

If you have a relatively new DeWitts OE replacement radiator and are experiencing "overheating", which you have not defined, then the culprit is likely either the spark advance map, like a dead or incorrect VAC, or the fan clutch. Most modern replacement fan clutches are "tuned" to the typical 195F thermostat opening temperature of later emission controlled engines, so they don't tighten until a higher radiator exit air temperature, which can easily cause coolant temperature to run in the 200-210 range in hot weather low speed traffic.

Keep in mind that the normal operating temperature range of these engines is 180-230F, and with a 50/50 glycol water blend and a 15 psi cap, the coolant boiling point is 265F, so you still have over 30 degrees boilover margin at 230.

Duke

I do have a back ground in heat transfer which I why I'm asking about air flow - thanks. How do I know it's overheating? Yes, I watching my 42 year old temp gage and understand it may not be accurate. I use it as a relative indicator. However, as the temp gage begins to soar and the engine starts to run like crap, I'm associating the two and believe that's what's' happening especially since it only happens on hot days in stop and go traffic or at a constant idle.

I will take a closer look at the other components, was just hoping to learn a good air flow number.

Thanks!
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Old 01-12-2018, 05:53 PM
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Originally Posted by davekp78 View Post
You could try a heavy duty fan clutch and 7 blade fan. I have no problem using these and the OEM radiator with vintage air here in Florida.
My goal is to have the car not overheat with stock components. I've thought about spiral fans, etc, 7 blade fans, etc, but that would not be correct for the car.

Thanks!
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Old 01-12-2018, 05:55 PM
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Originally Posted by 65vette396 View Post
I have a 7 blade fan on my 67 300 ac coupe and she runs cool all the time. I think installing the lower seals and the wide rubber one on top of the core support will help direct airflow thru the radiator.
My goal is to have the car not overheat with stock components. I've thought about spiral fans, etc, 7 blade fans, etc, but that would not be correct for the car.

Thanks!
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Old 01-12-2018, 06:21 PM
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Originally Posted by Nalrops View Post
My goal is to have the car not overheat with stock components. I've thought about spiral fans, etc, 7 blade fans, etc, but that would not be correct for the car.

Thanks!
Then get your entire cooling system back to new like OEM standards. Go though your spark Advance map and timing and carb adjustments to OEM specs and you should be god to go
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Old 01-12-2018, 06:23 PM
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Originally Posted by Nalrops View Post
I too, like many others here have problems with overheating in stop and go traffic. Over the years I've tried many things but to no avail. Time to start taking a more objective approach. Does anyone know what the design air flow over a small block 300 hp radiator is supposed the be at idle motionless?

I ask because this is something that can be easily measured, then compared to design specs thus including or eliminating the fan or clutch.

has anyone ever measured the air flow? If so does your overheat and what kind of feet per minutes did you measure?

i have a new Dewitt's 66-124427 aluminumradiator, 50/50 antifreeze mix, etc.

hoping to gain some knowledge and insight.

Thx!
Dewitt also sales an electric fan to attach to their aluminum radiators. This will stop overheating and keep your engine from excessive ware.
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Old 01-12-2018, 06:31 PM
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Originally Posted by Nalrops View Post
Also, I've got no seals around the radiator but it's always been my understanding they weren't used on 66 models that didn't have AC.
Big mistake. Until you have the radiator well sealed all around, forget about even trying other methods.

Last edited by toddalin; 01-12-2018 at 06:31 PM.
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Old 01-12-2018, 06:35 PM
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The links below are informative articles on timing if you havenít already read them.

Timing in a nutshell - with a 300HP engine, the factory spec for initial timing is 6* advanced (I like 8*). Your goal is 24-32* of total advance (with VAC) at idle. My 300HP develops 26* of advance at 500RPM with a B26 VAC.
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Old 01-12-2018, 06:43 PM
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Originally Posted by Mike67nv View Post
The links below are informative articles on timing if you havenít already read them.

Timing in a nutshell - with a 300HP engine, the factory spec for initial timing is 6* advanced (I like 8*). Your goal is 24-32* of total advance (with VAC) at idle. My 300HP develops 26* of advance at 500RPM with a B26 VAC.
Thanks Mike. I'll take a look!
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Old 01-12-2018, 08:10 PM
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Originally Posted by toddalin View Post
Big mistake. Until you have the radiator well sealed all around, forget about even trying other methods.
EXACTLY! This is not rocket science and what the OP is asking for sounds like a typical engineer over analyzing the situation.

If you don't have the radiator sealed, at idle you are pretty much just "windmilling" the under hood heated air. With the radiator sealed, the original type fan with shroud and the fan sitting in the correct 1/2 in at the rear edge of the shroud it will suck air through the entire surface of the radiator. This is how the engineering team designed it at the FACTORY. No need to try and improve on it 50 years later. Unless you have increased the engine size or h.p. DRAMTICALLY there is no need for anything else. This assumes your radiator is not plugged, in good condition, no collapsed hoses and your engine is tuned and running properly. It is pretty hard to out engineer an auto company that had to satisfy customers in all climates all over the country. People just keep trying to reinvent the wheel though.
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