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Old 04-27-2009, 03:05 PM
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Electric Fan CFM

I'm putting in a new sbc stroker and I want to trash can the whole clutch fan concept. I'm on summit looking at electric fans but can't decide what CFM I might need. They run anywhere from 1000 to 4000 CFM's. I don't want to break the bank but I want to keep the motor cool. Is there anyone out there with some experience who could push me in the right direction?

BTW it's going in an 80 Elky with a stock radiator.
Thanks
Darrin

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Old 04-27-2009, 03:22 PM
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the black magic fan is a good one. 2800 cfm. but they only rate it for 250hp with ac. You may want to rethink using the fan clutch.

I have seen good results with mid 1990's ford passenger car electric fans (V6 and V8). They have low and high speeds (3 wire).
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Old 04-27-2009, 03:27 PM
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Ok getting closer,
2,800 ish for 250 HP. The stroker got 450~500 hp, so I'm going to guess and say at least a 4000 CFM?
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Old 04-27-2009, 03:34 PM
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yep, you need a lot of electric fan. And those fans pull serious amps. They really tax the charging system. 20 or 25 amps is not uncommon.

the black magic fan pulls 17 amp, I believe.
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Old 04-27-2009, 05:41 PM
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Quote:
Originally Posted by dedub
I'm putting in a new sbc stroker and I want to trash can the whole clutch fan concept. I'm on summit looking at electric fans but can't decide what CFM I might need. They run anywhere from 1000 to 4000 CFM's. I don't want to break the bank but I want to keep the motor cool. Is there anyone out there with some experience who could push me in the right direction?

BTW it's going in an 80 Elky with a stock radiator.
Thanks
Darrin
The problem is less of one of CFMs and more of one of getting air flow across the entire core. We have lots of unhappy people writing on this forum that they bought the biggest flowing fan there is and aside from a lot of noise, they don't get much cooling performance from it.

What happens is that these fans pull a lot of air thru a small part of the core right in front of the blades. Multiple fans do a better job of drawing air over more core area, but often still not enough area is esposed to the air flow. It still comes down to having a shroud that encloses the perimeter of the core at one end and mounts the fan at an exit mouth at the other end. This allows the fan to make a pressure differential over the entire core which flows air over the entire surface area.

Fans that push are even less effective as they don't cause a pressure difference over the core except in front of themselves, so again much of the core isn't doing any heat exchanging.

So the key here is figuring out how to cause a flow over most, if not all, of the radiator core so it's giving up heat over all its surfaces. In the end you'll end up with something that looks like what came from the factory. Guys running traditional hot rods where there isn't space for shrouds have lots of cooling problems. The surface area for radiators in these 1920, 30, and 40 designs were inadaquate for 221 inch flat heads, it doesn't get any better trying to cool 350s, 400s, or 454s with the same area even with deeper cores and high pressure systems. So these things go critical very quickly.

Bogie
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Old 04-27-2009, 06:17 PM
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I used a licoln markVIII

Bought on ebay.relay from summit and the thing kicks *****.Always had cooling problems.Added an aluminum radiator and this Mark VIII fan and the thing is fantastic.All the Mustang guys swear by it.They say the black magic is a waste of money.I don't know if thats true but I was on a budget and it works.I have a BBC with a 671 blower.
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Old 04-27-2009, 07:32 PM
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Thanks for your input bogie,
I think I made up my mind. After reading your post and a few other threads, it seems the way to go is staying with your clutch fan and a good shroud. My first thought was electric would out perform a fan hands down. But to match the CFM, you need over 4000 CFM and that tends to be a noisy amp hog that just doesn't seem worth it.
Take care
Darrin
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Old 04-27-2009, 08:17 PM
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speaking from experience, i bought the dual 13 inch fan assembly from summit, made br derale. i have a 454 in an 81 malibu with a 3 core stock radiator, and it never goes above 195. a single 16 inch fan overheated after 10 minutes (230 degrees). aluminum radiator would be even better.
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Old 04-27-2009, 10:20 PM
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Electric fans are rated at free-flow, so once installed they might only flow half of what they're rated.

mechanical fans are usually rated at actual flow as installed, and are rated at 1800 rpms.

Comparing an 18" electric fan that says 3600 cfm to an 18" flex fan that is rated at 3200 cfm is no contest. The flex fan will move 4-5 times as much air at higher RPMs, and the electric might only flow 2000 as installed
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Old 04-28-2009, 07:07 AM
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Thanks curtis,
you just confirmed my choice.
For the rest of the electric fan fans (pun intended). I'm not knocking your choice, it's obviously working for you and I have to admit they look sharp, thus one of the reasons I wanted one in the first place.

Thanks to all
Darrin
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