pondering my heat dissapation options

while perusing the electric fan options in the jegs catalog, something peculiar caught my attention. now for an 'apples-to-apples' comparison i'm going to use flex-a-lite as my example, assuming the motor and shroud is the same.
jegs lists the following:
16" puller, rated at 2500cfm, 18.5 amps straight blade design.....list price: $143.99
16" puller, rated at 2010cfm, 13 amps "syclone" curved blade design.....list price: $114.99
so my question is, why even make the curved blade design if they are apparently less efficient than a straight blade design?
now personally, i see how the curved blade would actually be more efficient but if their cfm and amp data is accurate, it contradicts my theory, and the curved blade is less efficient. so why would they even offer such a thing? just doesn't seem to make sense to me.
any theories?

clutchdust said:

16" puller, rated at 2500cfm, 18.5 amps straight blade design.....list price: $143.99
16" puller, rated at 2010cfm, 13 amps "syclone" curved blade design.....list price: $114.99
so my question is, why even make the curved blade design if they are apparently less efficient than a straight blade design?

Click to expand...

2500/18.5=135CFM per ampere

2010/13=154CFM per ampere

It would appear the "cyclone" is more effecient to me.

I would wonder which uses less amperage under dynamic conditions where the air forced into the rad from vehicle speed reduces current usage,.

maybe i should clarify my version of efficiency. while not disagreeing with your math, my intention was to compare the volume of air moved through similar size fans. i would expect amps to follow in proportion to cfm. i'm just surprised at the lower volume of what should be a more efficient blade design.

According to Tom Dewitt these fans can be rated totally differently depending on the maker's test setup...some rated with radiators in front, maybe eben a/c condenser too, and some with open air, some on a board or into a box, really hard to say that a ways.....

all I know is I have Dual Spals with them totally sealed to the backside of a '89 F body V8 radiator that is the same core size as stock for my '72 SBC vert.....

it' cools fine, pulls it down very quickly....
with those rubber flappers opening at speed, I actually have a overcooling condtion in cold weather at speed, drilled too many holes around my t-stat....can't win.....

:flash:

The only reason they make the curved blade fans is for noise.
Almost all oem fans are curved.
It's in Spal's docs somewhere.

I run a big Spal straight fan to run with A/C only and people turn around to look a block away. Sounds like a helicopter over your head.

010752, thanks for the heads up. i went to the spal website and found this:

spal FAQ said:

Q. What's the difference between the straight blade fans and the curved blade fans?

A. The straight blade fans provide maximum cooling for their size. The curved blade fans sacrifice a small amount of performance in return for a much quieter fan. If noise is an issue, go with the curved blade fans. If ultimate performance is the objective, use the straight blade fans.

Click to expand...

honestly, this surprises me somewhat as i figured the curved blade design would be inherently more efficient at moving air. it seems to me the leading edge of the blade would 'cut' better and send air down into the arc of the blade so that for the same diameter, the curved blade should move more air. inversely, much like the old aircraft wing and automotive racing wing, the straight blade looks like it would allow more air to 'spill' off the leading edge.
that was my theory anyway. looks like i'm all wet.

clutchdust said:

010752, thanks for the heads up. i went to the spal website and found this:

spal FAQ said:

Q. What's the difference between the straight blade fans and the curved blade fans?

A. The straight blade fans provide maximum cooling for their size. The curved blade fans sacrifice a small amount of performance in return for a much quieter fan. If noise is an issue, go with the curved blade fans. If ultimate performance is the objective, use the straight blade fans.

Click to expand...

honestly, this surprises me somewhat as i figured the curved blade design would be inherently more efficient at moving air. it seems to me the leading edge of the blade would 'cut' better and send air down into the arc of the blade so that for the same diameter, the curved blade should move more air. inversely, much like the old aircraft wing and automotive racing wing, the straight blade looks like it would allow more air to 'spill' off the leading edge.
that was my theory anyway. looks like i'm all wet.

Click to expand...

Pretty sure a nuclear sub prop looks like the curved fans, less noise.....

silent running....I used to be a reader into subs and warfare tactics....LOVED Tom Clancy's book....Red October.....having said that, my Spals DO sound like a nuclear power shop vac.....

If the curved blade fan uses less amps it is probably a smaller motor turning it. That might be the reason for the lower cfm.