4 Blade vs. 6 Blade vs. 6 Blade-Flex Fans

[Guest]

Even though it seems that my car is OK with the original 4 blade fan in South Texas, I will feel better with more cooling margin.

So, today I am changing the original 4 blade 18.5 in. dia. fan for a 6 blade 18 in. fan. I actually had thought that I had ordered a FLEX FAN with wider Aluminum flex-blades, but I actually ordered and received a 6 blade fixed blade fan.

I am thinking that with the same pitch angle and a 33% increase in blade cord and a negative 5% for 18 in dia vs 18.5 in dia, I should have a 25% increase in air flow.

Question:
Is it reasonable to expect this result ?

Is the 6 blade FLEX fan better than a 6 blade (fixed) as compared to the original 4 blade (fixed) or am I splitting hairs ?

Note: no shroud.

"The more you know, the more you know how much you don't know"

[Alexander]

RE: 4 Blade vs. 6 Blade vs. 6 Blade-Flex Fans

The difference between a flex fan and a fixed fan is what happens at higher RPM's. Flex fans were developed to reduce energy consumption. At higher RPMS, the blades of the fan flex and flatten out perpendicular to the axis of rotation. In theory when your car is going 60 mph on the freeway and is engine is going at 2000 RPM's the fan is unnecessary since the air is going through the radiator at 60 mph. The flex fan is offering little drag with the blades flat, so it is saving you gas on the highway. It is an imperfect solution as if you are stuck in trafffic and the tmeperature of egine is rising, raising the RPM's of you engine higher will not increase airflow through the radiator.

Clutch fans have a similar limitation, that is whey flex fans with bimetallic thermostats were developed. Ultimately, electric fans are the best solution as turning on the fan when necessary.

There are a lot of variables for airflow with fans. In general more blades are better. The amount of airflow also depends on how close the fan is to the radiator. A fan shroud helps airflow a lot.

Alexander
1959 Hardtop
1960 Golde Top

[JohnG]

RE: 4 Blade vs. 6 Blade vs. 6 Blade-Flex Fans

I can only comment on the 6 blade rigid fan. I have had a 4 blade fan for 3 years. The cooling was marginal, even with a 160 thermostat in a New England summer (upper 80s, worst case).

I installed a 6 blade fan and went on a long trip a week ago. The trip was highway driving at 65 - 75 mph with some slow downs for traffic jams and toll both lines. I was extremely pleased to find that the temp never went over 175, staying at 170 most of the time. I am much more confident in the car as a result. Outside temp was a little under 90, worst case.

I should add that the radiator had been rebuilt and the block cleaned out when I rebuilt the motor so there were no other weak spots in the system.

I have a shroud but have yet to install it - another project. If you can go with a 6 blade fan and a shroud then any comments I have read on this discussion board would suggest you have it made!

The only other thing I learned was that I am going to add some more insulation under the console! That area gets pretty warm, probably in part due to the heat getting moved back from the motor and radiator.
John

[tbirdave]

RE: 4 Blade vs. 6 Blade vs. 6 Blade-Flex Fans

Where are you getting your fan blades and shrouds? tbirdave

[Guest]

RE: 4 Blade vs. 6 Blade vs. 6 Blade-Flex Fans

I bought the fan blade off of EBay. I may try to fit a 1957 Chevy type of circular shroud (custom fitted) on the radiator. The main thing is to not recirculate the air, so a complete enclosure is not necessary but is an improvement.

[Alexander]

RE: 4 Blade vs. 6 Blade vs. 6 Blade-Flex Fans

Many here have used the fan shroud from Dearborn Classics with success.

http://www.dearbornclassics.com/cgi-bin/more_info.cgi?part_number=fs12

Alexander
1959 Hardtop
1960 Golde Top

[JohnG]

RE: 4 Blade vs. 6 Blade vs. 6 Blade-Flex Fans

I got the 6 blade fan on Ebay. I doubt it was ever on any TBird; just a Ford engine. If you do this, make sure the clearance to the radiator is ok; you might have to get the spacer machined (having a second spacer to play with is good...).

I have also seen 6 blade fans in some TBird supplier catalogues.