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Joe K · 02-05-2023, 09:37 PM

The other aspect which is frequently not considered is that with EITHER 2 blade or 4 blade, you get the car above about 20mph, and the velocity air flow CFM naturally EXCEEDS that of the fan when stationary. I.e. the fan actually holds back the air - or perhaps more accurately "measures it out."

So it may make sense that a 4 blade may hold it back MORE EFFECTIVELY.

I have a couple of aftermarket fans, a 2 blade I have used, and a four blade that came with the Gordon-Smith Compressor. Somewhere I have seen that Ford installed the 4 blade on trucks and industrial engines - and the Gordon Smith setup would qualify.

I've also seen that while less likely to fail than an original fan, even the period Western-Auto, Pep Boys, JC Whitney pressed metal fans can fail, commonly at the bolting holding the fan to the pulley casting. Rather not the bolting but the "weak spot" presented by the four drilled holes. The centrifugal force "tears" apart the sheet metal between holes.

My choice today is the Cast Aluminum two blade.

Joe K

02-05-2023, 09:37 PM	#7
Joe K Senior Member Join Date: Jul 2010 Location: Cow Hampshire Posts: 4,188	Re: 2 blade or 4 blade fan The other aspect which is frequently not considered is that with EITHER 2 blade or 4 blade, you get the car above about 20mph, and the velocity air flow CFM naturally EXCEEDS that of the fan when stationary. I.e. the fan actually holds back the air - or perhaps more accurately "measures it out." So it may make sense that a 4 blade may hold it back MORE EFFECTIVELY. I have a couple of aftermarket fans, a 2 blade I have used, and a four blade that came with the Gordon-Smith Compressor. Somewhere I have seen that Ford installed the 4 blade on trucks and industrial engines - and the Gordon Smith setup would qualify. I've also seen that while less likely to fail than an original fan, even the period Western-Auto, Pep Boys, JC Whitney pressed metal fans can fail, commonly at the bolting holding the fan to the pulley casting. Rather not the bolting but the "weak spot" presented by the four drilled holes. The centrifugal force "tears" apart the sheet metal between holes. My choice today is the Cast Aluminum two blade. Joe K __________________ Shudda kept the horse.