Four blade, versus seven blade fan in my 225 Duster? Final report now in.

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cruiser

cruiser

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Hi All: I have a seven blade fan that came from a 1974 225 engine with a/c. It looks like it would fit my 1974 Duster non - a/c 225 engine. Would there be any benefit to changing to a seven blade fan? Looks like it would bolt right up with the existing spacer and would have no interference problems. Thanks - cruiser
 
cruiser said:
Hi All: I have a seven blade fan that came from a 1974 225 engine with a/c. It looks like it would fit my 1974 Duster non - a/c 225 engine. Would there be any benefit to changing to a seven blade fan? Looks like it would bolt right up with the existing spacer and would have no interference problems. Thanks - cruiser
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Do you have a shroud now?
 
I would think that steal 4 blade is heavy *** h e double hockey sticks.
I would change to the lighter more efficient one.
 
cruiser said:
No.
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Likely the pitch of the fan will determine how much air it moves. See how the air flow at idle is with the current fan, then put the other one on and see if there is a nice improvement. Other than that, if you have no interference issues, then why not?
 
I don’t think I would want a 7 blade non-clutch fan unless I needed it to solve an overheating problem. Seems like it would make a lot of air noise.
 
I have the same 4 blade fan. No shroud. The car doesn't overheat. Wouldn't a 7 blade fan offer improvement, especially sitting in traffic on a hot day? I would install it if I had it. And it will give you something to do and then let us know your findings.
 
jpl572103 said:
I have the same 4 blade fan. No shroud. The car doesn't overheat. Wouldn't a 7 blade fan offer improvement, especially sitting in traffic on a hot day? I would install it if I had it. And it will give you something to do and then let us know your findings.
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Okay, I'll install it and let you know how it works out after running it for awhile.
 
The 4 blade fan is a "fuel economy" special. Low blade pitch, doesn't move a lot of air. A/C and HD models got more blades, but the effect was mostly from the higher blade pitch. You probably can't detect the noise difference on the highway, but they will be noisier at idle. As you would expect, they will move much more air at low engine speed.

I used to have a 7-blade fan from a 383 on my Commando 273 — at fast idle it was like a hurricane... blew dust and papers down the street. I replaced it with a clutch fan to see if I could even slightly improve the fuel economy. Never had any overheating issues, though.

On my last slant I installed a Texas Twister flex fan. That did seem to help with cooling in hot weather. I didn't have a shroud, either.
 
Is the car over heating now? If not, there's really no benefit. In fact, it will cost power and mileage.
 
I have an OEM 7 blade fixed fan on my 67 273, no particular extra noise.

I suspect the 4 blade fan has a steeper pitch than the 7 and might create more noise.

Both should work just fine with the correct wp and pulleys
 
I'm pretty sure six (maybe more, but probably not) heater cores plumbed together in the core opening would be able cool a mechanially sound well tuned slant... Only place I've seen where a larger fan would be needed is for the aforementioned AC car.
 
Garrett Ellison said:
I'm pretty sure six (maybe more, but probably not) heater cores plumbed together in the core opening would be able cool a mechanially sound well tuned slant... Only place I've seen where a larger fan would be needed is for the aforementioned AC car.
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Okay, here's my final report after doing the fan swap. The seven blade fan bolted right up to the engine using the existing pulley and spacer. There were no interference issues with radiator hoses or anything else. The fan definitely moved more air than the four blade fan. There was no noticeable increase in fan noise. The engine didn't cool any differently than the four blade fan, as RustyRatRod predicted. I didn't have the opportunity to try it in very hot weather, so I can't speak to that issue. But it definitely kept my slant six nice and cool, and I can see how the shrouded seven blade fan with the wider radiator would be very efficient in the slant six a/c cars. So it was an interesting experiment and a fun project to tinker with, but the final conclusion is that the un-shrouded four blade fan is just fine for normal operation. I believe that it was just cheaper for the factory to put in a four blade fan and save fifty cents on every non-a/c car that they built. For whatever its worth, the seven blade job looks really cool in the engine compartment to my way of thinking. If you're going for looks, I'd definitely try it. Thanks to all for your input. It's a beautiful Saturday, and I'm going for a ride in Dusty!

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Ohh, that's a keeper! Beuatiful color combination, and I'd drive the wheels off of that, too!
 
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