4 or 5 Blades. Which is better? radiator cooling

[ZGN]

The Stock FD Fans have one 4 blade fan and one 5 blade fan. Why is it done this way?

[djmtsu]

I believe one does not come on until the A/C is on.

But I am an FC guy.

[0110-M-P]

Yes, they come on at different settings (temp/ac). I have both mine set to come on at the same temperature and I don't have a/c. However this doesn't really answer the question of which is better. I would assume the more efficient fan comes on first and the second fan is just for that extra airflow, but I could easily be wrong.

[ZGN]

A 4 blade seems like it would require higher speed to = the same amount of airflow of a 5 blade. If this is true then why would mazda use a 4 blade fan on one fan and a 5 on the other. There has to be a reason.

[David Jerome]

From my readings back in the day(2-4 yrs ago) I remember some thought it best to run 2 4 blade fans. I dont know if there was ever a proven difference or not. I do know the stock fans are extremely efficient.

[Dr-Rotor]

Guys.....the reason for the whole thing is Noise. If you look carefuly at the fans you will see that the blades are not even spaced evenly apart. Mazda designed it this way so that when both fans are running they cancel eachother out to make a nice quiet system.

Its harmonics, thats why one fan has 4 & the other has 5 blades. Much like a 2 blade helicopter has a much louder rotor slap than a 5 blade system that has more of a buzz than slap like the Hueys do. This is why the rear tail rotor on the Apache is not an exact cross pattern, its to loud. So they moved the blades closer to eachother to reduce noise. Same reason why those helis with the inclosed tail rotors are so quiet like the Comanche.

Sorry for the heli talk but thats the only way I could give the right example.

[ZGN]

which one do you think is more effective in cooling? 4 or 5 fans? I am about to replace mine and it would not be any trouble to make them both 4 or 5 bladed fans.
I would think 5 blades would be more effective. anyone know for sure?

[warwickben]

it depends on alot of things. the angel of the blades and and the surface area ect ect.

[Phoenix7]

well, if I'm reading right then it's mostly for noise pollution since the CFM they pull should be at a minimum: 2100CFM.

If you go with a 3000CFM aftermarket fan it wouldn't matter if it's 4 or 5 blades because the number of blades is related to noise and not performance, right?

a 3-blade, 3000cfm fan = 5-blade, 3000cfm fan?

[Dr-Rotor]

Originally Posted by warwickben

it depends on alot of things. the angel of the blades and and the surface area ect ect.

^^^^ What he said.

[Dr-Rotor]

Originally Posted by phoenix7

well, if I'm reading right then it's mostly for noise pollution since the CFM they pull should be at a minimum: 2100CFM.

If you go with a 3000CFM aftermarket fan it wouldn't matter if it's 4 or 5 blades because the number of blades is related to noise and not performance, right?

a 3-blade, 3000cfm fan = 5-blade, 3000cfm fan?

^^^^again what he said too....basicly if the fans you want flow more CFM than stock then they will be more efficiant. Hope we have helped.

[ZGN]

Thanks, I'll just keep them the way they are.

[Trout2]

I can't remeber the specifics but I remeber reading something about upgraded fans in the 99 FD.

Jack

[Herblenny]

Far as what I remember... its not noise but SMIC duct behind the fans.... which puts restriction on the flow and require harder pull (4 blade fan). In 99+ mazda put 7 blade fan vs. 4 blade fan in 93-98..

Is you are going with FMIC (like me), go with 2 x 4 blade fans as you no longer have duct behind the fan and also want maximum flow.

[dudemaaan]

I have heard the 4 blade fans flow more. But i don't know what proof there is on this. Also both fans always come on together, not one at a time. They do have different fan speeds though depending on which relays are activated. I will run my fans tomorrow and see which one physically feels like its moving more air.