Radiator scientists, gurus, and wizards- lets discuss

This is a spin off from this thread
http://www.jalopyjournal.com/forum/showthread.php?t=791794
In hopes of a more general discussion.

Ok now here's some things I find puzzling.

Ill admit fully that when it comes to radiator sizing I'm sort of light on information.
And new to blown hemis
But I fully understand just about any OEM cooling system ever built.

Seems these aftermarket radiators are rated to cool a certain HP level with the premise that a 3000 Cfm fan is used. Yet the engine is not making anywhere near its potential HP while stuck in traffic or light cruising. As RPMs rise so does HP level as seen on any dyno graph. Usually ( burnouts excluded) as the Rpms come up so does speed and natural airflow across the radiator. At speed the natural airflow across the radiator renders the fan nearly mute.

Maybe I'm overthinking this but it makes no sense at all when the exact same radiator is speced to cool 600 HP with 2600 Cfm and 750 with 3000. This just sounds like BS to me.
I don't know of any engine generating 700 hp idling in a traffic jam or cruising at less than 30 mph. At speeds below 30 is when the fan is most important.

 

Oh and what's the Cfm of a lets say stock 7 blade clutch fan at idle speed ?
That's a popular interweb question with no answer

 

Sometimes it don't pay to think to much. Like you I have no idea what HP has to do with cooling. I have an A.M.X. with 600 hp running a Stock Rad. It runs low 10's. No cooling issues. I'm building a new Super Gas car with 1,000 hp (not blown) on the Dyno and it is running a smaller Rad with no issues than the A.M.X. Now understand these are not street cars but if HP had anything to do with Rad size shouldn't I need a larger one for my new car?
The Wizzard

 

Interesting. What fan/clutch/shroud setup?

 

Also, and I don't know the mathemeatical equasion, doesn't H.P. in some way equal heat? And also, blowers make A LOT of heat?

 

Don't have the answers but do know this. Same rad, coolant, engine, etc...

22x19 dual 1" core aluminum rad with a 2200 cfm puller fan. Stout 440 Mopar with 727 auto trans.

The car ran very cool above 35 mph, but in stop and go 100 degree summer traffic the temp would creep up to 220.

Added a 1750 cfm pusher to the existing setup and the problem went away. Can idle all day in 100 degrees plus and not get over 195.

 

most of us are hotrodders and not scientists. The rest are just bullshit artists. I'm a hotrodder.

 

I'm not quite sure what you mean by that tommy but yea I'm a hot rodder too.

 

So the A.M.X. has a 24"x21" 3 row core in it with 2 - 12" pull fans and no shroud. It's basicly a stock rad. The new car has a Ron Davis alum 22" x 16" 3 row rad with 1 - 15" pull fan and a shroud. I also have a Blown street project on the back burner so I want to know what will or will not cause me issues when I get to that point.
The Wizzard

 

There is more to it even, like how does the hot air get out of the engine compartment? Thats why cars without hoods can run a bit cooler.
The first setup for my Rambler I made a shroud to cover the whole rad and it cooled great ideling, but on the highway got hot, so I remebered my VW Rabbit, it had little rubber flappers on the shroud, to let hot air through at speed, I added those and Bingo, all good. But most people have low speed issues, I always recommend largest rad you can fit and a largest shrouded fan you can fit( or two smaller puller fans). I put the Flex-a-lite kit on my 2000 Sierra and it was way better than the mech fan, quieter, more power, ac colder,etc. So I would add, that study how the O.E.M. does it and try and copy it, lots of good ideas out there....

 

Comments like this are just a waste of space. If I give advice it's because I have already proven it will or will not work. Till then I'd rather say nothing than sound like a know it all or a Smart Ass.
The Wizzard

 

Yes, HP does convert to heat - lots of math but ...

1 watt is approximately 3.413 BTU/h
1000 BTU/h is approximately 293 W
1 horsepower is approximately 2,544 BTU/h

Blowers generate their own heat that effects the air fuel charge .
Secondly blowers should be increasing net HP and that needs to be handled by the cooling system.

 

Here is a Mock up shot of where I'm headed. It's come a good bit further since this photo.
The Wizzard

 

There is a factor between hp production and heat, measured in BTUs. These are rough numbers. About 30 percent of the energy produced by the engine is converted to heat in the cooling system..more or less. So if you make 600 hp you can guess that while at that level you will need to deal with 30 percent of that energy in the form of heat in the cooling system.
That is only ok at steady state running and energy production so you are correct that idling does not produce 600 hp or the heat going into the cooling system.
Anyone who claims a one sized fits all system, "system will handle 600 hp" is pushing the truth..a bit.
I have found that in most cases problems in cooling are caused by moving the coolant too fast through the heat exchanger/radiator, or by not moving enough air through the heat exchanger.
A good cooling system should not be dropping the coolant temp more than 20 degrees across the radiator under any condition.
If the coolant is going in at 200 then it should be going out at 180+/- 2 degrees.
The best fan is one that is shrouded and leaves 20 to 30 percent of the fan inside the shroud. The fan is in fact a centrifical pump and needs a place to sling the heated air.
I have always had cars that created negative pressure in the shroud. If you are creating negative pressure between the fan and the radiator you can move no more air than that through the heat exchanger.
A good seal around the shroud at the heat exchanger and a tight fit at the fan blades is a must for proper cooling.
IMHO flex fans are not good centrifical pumps and in many cases cause more problems than they fix.
Your results may vary.

 

Here's a dyno graph of an engine capable of nearly 1000 HP.
Nothing special just a random pick & the first one I saw.

Notice how low the HP is at cursing Rpms in the 200-300 range .
Apparently this would not need much of a radiator for normal and sane rpm driving if one were to use the same standard as the manufactures of after markets are using. Remember I think it's bs. Also simply increasing the airflow according to them would make the same radiator capable of providing cooling for more HP.

I would think that at 70 mph the natural Cfm flow would far exceed the 2600 to 3000 Cfm of an electric fan.

I'm still trying to figure the Cfm movement of a stock 7 blade clutch fan at idle or near idle speeds.

 

I could see the aluminum rad , single fan with shroud cooling better , more efficiently than the other.

Is the other a copper and brass ?
The shroud makes a big difference on efficiency
Aluminum sheds heat faster than copper too.
What's the cores look like as far as spacing and fin count ?

 

It sounds like you say that 30% of 600hp would be heat loss to the cooling system. I believe that is incorrect by a large margin - the power that you get out of the engine is only about one fifth or quarter of the energy of the fuel you have burned, the rest is lost as heat - some through the cooling system and more with the exhaust.

These kind of numbers are always quite vague since few can measure them and no two engines are the same, but I've seen rough estimates saying that ~25% of the fuel energy is turned into actual work (power), ~25% is lost through the engine cooling system, and the remaining ~50% is lost in the exhaust. Assuming that those numbers are in the ballpark, a 600hp (about 440kW) engine should need to cool away 440kW of raw heat with the cooling system at full throttle.

 

Copper transfers heat much better than aluminum.

http://www.hotrodhotline.com/md/html/aluminum_vs_copper.php

 

It's roughly equivalent to the airspeed velocity of an unladen swallow.



...

Seriously, that's not enough information (as I think you already know). Thermal or mechanical clutch? How hot is is and what was the engine most recently doing? What's the shroud look like? Enclosed engine compartment? Etc etc etc.

I think the most useful way to quantify fan airflow is with only two categories: "enough" and "not enough". You'll know "not enough" when you see it.

 

Yes. Copper and Brass. Also another factor to that rad doing a good job may be that the Motor has Alum. heads on it. I don't remember the tube count but I is a newer style core that was put in the stock tanks and straps. Here is a shot of the non H.A.M.B. car doing it's thing.
The Wizzard

 

Here's something to consider. An old guy I know that's been building cars for street and racing for since the 50's told me what he learned was that the amount of water in the radiator should equal the amount of water in the engine. Not exactly, but close.

He says one of the things that got him to realize this was hemi's and Fords have more water in the engine than Chevys. And that the radiator water capacity needed to be increased in those engines. He said chevy radiators had a lesser water capacity, and less in the engine, and that influenced how much cooling got done in the core. So he tries to get a radiator that is close to the volume of the engine,

Not my theory, but I trust this guy.

 

G-son you are correct but you just read too much into my words. I only dealt with the cooling system in regard the question and the problems one might encounter while fixing things.

I did not say that all the heat went to the cooling system. If one were to look you would indeed find that about 75 percent or more of the heat /energy created in an internal combustion engine is wasted. About 30 to 40 percent goes out the tail pipe, other than the cooling system, the rest goes out via places like oil coolers and heat radiated of the engine. In either case none of us would want to eat the way our engines eat. If we did we would take one bite out of each burger and toss it and go back for another and so on till we were full. We don't eat that way but we like to drive our cars that way.

S Mazza

Is that a European Swallow?
Time to explode.

 

This makes sense,
If there's 3 gallons getting heated in an engine and one gallon cooling off in the radiator, the ability to raise the temp out weighs the capacity to cool it off.

 

31 Vic and Fullblast bring up a number of good points. Tommy, lets allow for a few more categories!
Three cooling strats come to mind of interest:
1. idling in slow or non-moving traffic in increasing engine temps.
2. slow speeds with increased loads at high ambient temps.
3. high HP demands at high 'summer' temps.
Full blast has some methods of ensuring adequate airflow for cooling.
For the most part, I'd want to have more cooling capacity, than heat generating capability...yeah spoken as an injuneer, but think about it fer a minute. Full Blast has it right. Proper rad size for worst case scenario, good shroud design, vent flaps that work at speed, and an effective fan.
I have a low and high speed fan switch, for moderate and worst case cooling demands.

 

Oh, you have to know these things when you're king, you know?
http://www.youtube.com/watch?v=y2R3FvS4xr4

Sort of. But it's affected greatly by such exciting factors as:
- Internal surface area of the engine (in the chambers and oiling system)
- Internal surface area of the engine (in the water jackets)
- External surface area of the engine
- Internal surface area of the radiator
- External surface area of the radiator
- Mass airflow across the radiator
- Mass coolant flow through the engine
- Specific type of coolant used
- Construction materials used in engine
- Construction materials used in radiator
- Weather
- Load on the engine

 

Well said. Still, circle track racing is one thing, and street driving is another. If you only use the maximum horsepower for 10 seconds out of every 10 minutes, then you have a tradeoff to consider. Do you need to lug around all that extra cooling capacity that will let you run at 100% "duty cycle"? Or accept some reduced duty cycle?

 

All great points, now how does one put a quantitative value on these .
Is there a way to determine this stuff like internal surface area? Does one need to accurately ? Or even in a relative format. Really the engine is what it is and the variable would be coolant flow and core size.

The ratings are based on HP , and I'm wondering if a 800hp V8 would need the same cooling as a 800 hp v6 or a tuners 4 banger. Most of the points you mention would be less

 

Given '31V's intentions, he'll want to cope w/hot day slow moving traffic heat balancing. If the Hemi and Blower make x number of btu at 110* ambient temp, then max fan/shroud, coupled to ideal (or grill shell) size rad opening, leaves only a question of how many rows are needed in the radiator!
We'll assume the water pump and thermostat are set up for the 'system' as planned.
Squirrel runs a blown big block, the heat loads would be similar...

 

As for the water pump and thermostat, I agree, "cheat" off the OEMs whenever possible! They already paid some guy to figure this out back in 1963!

(If we had to design all this from scratch, it really would be complicated. That's what I am getting at with my lists of factors. But fortunately, we don't really need to get into that, because we are working within certain parameters. That's where the "rules of thumb" come into play.)

That usage scenario may be the limiting factor. I don't think that is really a lot of load at all. At least, it's not much load if the blower has a vacuum-regulated bypass (which I would recommend).

I would suggest taking another look at an OEM's homework and figure, if you have a muscle car engine and want to use it like a muscle car, then aim for the same amount of radiator surface area that the muscle car had.

 

I have found a lot of variable come into play when cooling and engine. I bought a 200 4R rated at 500 hp from a vendor who highly recommended I install an aluminum radiator for better cooling for warranty reasons. I've crammed a BBF in a 68 Fastback with an aftermarket hood that was louvered to help air flow and heat escape from the enclosed engine compartment. The fit was so tight the engine had to be lifted to change the plugs. Additives like water wetter help. In one case a fan shroud cured the overheating. On the grapevine last month, there was a amber alert sign that said turn off a/c to prevent overheating. Of course the weather affects cooling too. If their is a simple rule of thumb in spec'ing out a radiator I too would like to know.