Radiator--AFCO Double-Pass ???

[Prof]

Has anyone tried the AFCO double pass radiator? It is the right size for a Lone Star (22x19x2.5, outlet 4" up from bottom) yet it moves both Inlet and Outlet to the PASSENGER side of the engine compartment. Many Lone Star 427s have the flexible coolant hose snaking across the engine bay to the driver's side. Why? Is there something in fitting the body or hood that prevents using an Upper Inlet on the PASSENGER side?

See also AFCO's specs http://www.afabcorp.com/AFCO_Dynatech_USbrake/merchant.mvc?Screen=PROD&Store_Code=A&Product_Code=80100NDP&Category_Code=ct_dbl-pass-rad


Don't read this: I ask because Smiley's Racing in Mesquite has several of these marked waaay down (display models) and I have a TON of store credit after returning all of my heims and swage rods (IRS coming). I have two Lone Star radiators for SBF (old stock/old style/or trade-ins when customers changed to big block). One is a Griffin, the other an AFCO. The double pass style at Smiley's is identical...with upper inlet on passenger side.

Anyway, thanks again for helping a newbie,
Paul
McKinney

[Reptyl]

Prof,

I haven't tried one in the Cobra, but I helped my buddy install double pass radiators in his race cars and they worked great. I don't see any reason why it wouldn't fit the LS if the cores are the same size. The inlets are on the same side due to the double pass design.

RT

[IndyCobra]

The problem I would see as far as my car goes is that I couldn't fit a radiator with an outlet on the passenger side. I'm sure you've looked at this for your car so it may be a non-issue but on mine, it would interfere with the alternator big time. I only know this because I am still fiddling with getting the radiator to fit properly on my rig as I jiggle the body around.

[crazymat03]

I have the AFCO double pass radiator installed on my car, I dont recall the measurements but it was custom built from specs I provided. As far as cooling it works great, the only issue I have is that my outlet is too near the bottom of the radiator and rests on the steering rack, the driver side of the radiator had to be lowered slightly for the cap to clear the hood, so viewing head on it is obvious that my radiator is not quite level. I have a Ford 400M with a head/fill tank on the coolant outlet and approx. 6" of hose to radiator inlet.

Just make sure you take into account the height of the filler neck of the radiator, and that the outlet may be close or resting on the steering rack affecting how far you can drop the radiator between the cross members, and if the radiator cap is lower than the engine outlet you may need an additional tank or inline filler neck to properly vent air from the system.

[Roush #1]

Paul,
Before you install the radiator you might consider a drain cock. They sure come in handy and are very easy to install with the radiator out of the car.
Jody

[AggieJack]

Have you called the radiator folks to ask them about temp drops and efficiency?
I vaguely recall from thermo and heat transfer class that the greatest effect on efficiency is temperature difference between the two mediums (outside air and water temps). Also residence time.

Single pass has high temp difference for all flow and lower velocity hence longer residence time.

Double pass has high temp differnce on first pass and lower difference on second. Higher velocity and shorter residence time.

I may be overthinking this but it may be worth a call to ask the mfrs. Someone who's done thermo work more recently than me chime in here - please

AggieJack

[Skuzzy]

Jack, you are correct about resident time, but there is also surface area to consider. I had to think about it for a bit. Initially, I thought the same as you did.

A double pass design is akin to taking the radiator tubes and putting them end-to-end. This doubles the surface area for the double pass at the expense of doubling the velocity of the coolant flow over a single pass design. The lower velocity of the single pass design moves twice the coolant as the double-pass design of the same surface area.

It all boils down to the thermal conductivity of the coolant. If the velocity of the coolant reaches a point which exceeds the thermal conductivity of the coolant, the engine will overheat. As long as the coolant velocity is below its thermal conductivity threshold, there should be no notable difference between single and double pass designs with the same surface area.

[AggieJack]

Skuz,
Actually the surface area doesn't change. Same number of tubes, linear inches, diameter. Just with double pass you have first pass with high temp differential and the second pass at a lower differential is the way I'm looking at it - all other factors equal. Now you've got me thinking

Seems most performance radiator mfrs make single pass but 2-3 rows of tubes.

Love to see detailed analysis. Good topic.

AggieJack

[AggieJack]

Here's a link for brave reading. Interesting. Haven't finished it yet - still reading and thinking.
http://forums.bit-tech.net/showthread.php?t=100862
and
http://importtuner.automotive.com/11215 ... index.html

second article says dual pass not generally recommended.

food for thought.

AggieJack

[Skuzzy]

Jack, let's toss some arbitrary numbers around.

I am going to keep this simple just to demonstrate what I was talking about.

Let's take 2 pipes, each 24 inches long and 2 inches in diameter. Each pipe has a volume of 75.4 cubic inches (roughly). Given that, each pipe will hold 1.95 U.S. gallons of water. (check my math here guys).

Now, let's take a pump moving water at a fixed rate of 10gallons/minute.

In the single pass design, each pipe will be carrying 3.9 gallons of water, or 2.56gpm.

In the dual pass design, each pipe would carry 1.95 gallons of water, or 5.12gpm.

The total surface area of the pipes are the same. The difference is the single pass is breaking down the flow into two 24 inch long pipes. While the dual pass is actually pushing all the water through one pipe 48 inches long, just happens to flow twice as fast.

That make more sense? Or am I pouring water all over myself?

[AggieJack]

I got that part. Surface area is same just velocity is half in single pass. If designed correctly, though, single pass SHOULD use twice number of tubes of lower diameter to keep velocity up - turbulent flow seems better in this case than laminar. If not then laminar flow in single pass may lower efficiency unless they do something to internal geometry to creat turbulence. hopefully they didn't just take a single and make into a double.

I edited above post to add another link. Says radiator companies they querried were not generally infavor of dual pass for this application.

We may be boring everyone else by now but this is a good discussion. Makes me expand my small mind.

AggieJack

[Skuzzy]

Well, now you are changing the parameters on me.

My arguments were predicated on the number and size of tubes being the same for both designs.

Yes, I agree smaller tubes and more of them is always better unless the tubes have internal fins, then it all changes again.

And yes, I am in favor of the single pass design due to the lower velocity flow rates. You run less chance of exceeding the thermal conductivity of the coolant. Turbulence is good and for those designs, such as using internal fins to swirl the coolant through the tubes.

The single pass crossflow radiator is a well proven design.

I think dual-pass will work just fine, but it does come with an added concern about moving the coolant too fast.

I cnanot imagine this being a boring conversation. Hehe.

[Barnsnake]

No solid science here, just a shade-tree opinion.

If the two radiators are the same area and thickness I would expect the dual pass to be slightly less efficient. The single pass exposes the greatest area to the highest differential between the coolant temperature and the ambient air temperature, at a lower velocity. Additionally, depending upon how the two passes are separated, the first pass may be transferring some of its heat to the adjacent part of the second pass.

If that is true, the only advantage of the dual pass is the inlet and outlet on the same side.

Good question.
Jim

[Skuzzy]

I have to admit I was playing a bit of devil's advocate. I do that. And while mathematically, the single and double pass designs would be essentially equal to the task, in practical applications I agree the single pass should be more efficient in this application.

[crazymat03]

Dont forget that you can contact the manufacturer and talk to one of their engineers. AFCO was very helpful in my case, they already have the formulas that take into account flow rate, pressure, transfer coefficients of the tubes and fins internally and externally. Any radiator manufacturer should be able to give you a BTU transfer rate (often listed as a HP rating) for their products. Call and ask, if you can transfer the same amount of heat out the system with one or the other than it really is just about where you want your outlets.

[Prof]

THANKS everyone. A lot more info here than I ever imagined.
I have several purge tanks that will clean up the snaking radiator hose to the driver's side.
Brian thinks I will have hood clearance issues. I may set my motor down pretty low and very far back.
Again, thanks everyone.
Paul