Reducing blades to two on cooling fan - Alfa Romeo Bulletin Board & Forums
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post #1 of 21 (permalink) Old 10-18-2017, 05:50 PM Thread Starter
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Reducing blades to two on cooling fan

An old article in the Alfa Owners newsletter of April 1976, the Technical Editor, Joe Benson Said: "Believe it or not, the largest single performance gain is to be had by modifying the engine fan; the effect can be felt from 3000 RPM upwards." "Cut off all but two of the blades (opposite of course)"

I'd like to hear from anyone who has actually done that.

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post #2 of 21 (permalink) Old 10-19-2017, 11:30 AM
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I have seen this on period Fiats of the time but never a hacked Alfa fan.
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post #3 of 21 (permalink) Old 10-19-2017, 11:37 AM
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I can not remember who or when...fan removed and electric fan installed on an early Sprint GT

The older I get.. the faster I was....
Tom
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post #4 of 21 (permalink) Old 10-19-2017, 12:09 PM
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Shankle stated that the stock fan consumes 7 HP at 6000 rpm.. A good reason to go electric.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

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post #5 of 21 (permalink) Old 10-19-2017, 05:53 PM
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I used to run without a fan all the time ... wouldn't consider it in current traffic.

Have an Autodelta fan in one car with all blades cut down to about 1.5". It won't cool enough even with a three row high efficiency core in standing traffic ... putting on the heater in hot weather almost does the trick. It's still in the car for looks but an electric SPAL pusher now sits in front of the radiator.

With a modern high efficiency radiator core a small electric pusher is all you need.

If you don't want to go electric, the smaller 1300, 1600 fan will use a bit less power.

I wouldn't consider taking out all blades but two in current traffic - never mind the potential hassle of having to balance the thing afterwards.
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post #6 of 21 (permalink) Old 10-19-2017, 06:03 PM
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I used to run without a fan all the time ... wouldn't consider it in current traffic.

Have an Autodelta fan in one car with all blades cut down to about 1.5". It won't cool enough even with a three row high efficiency core in standing traffic ... putting on the heater in hot weather almost does the trick. It's still in the car for looks but an electric SPAL pusher now sits in front of the radiator.

With a modern high efficiency radiator core a small electric pusher is all you need.

If you don't want to go electric, the smaller 1300, 1600 fan will use a bit less power.

I wouldn't consider taking out all blades but two in current traffic - never mind the potential hassle of having to balance the thing afterwards.
IMHO the original rads are ALMOST as good as any .... boiled out and flow tested no issues whatsoever....I think I am going to totally remove the fixed blade and install a low amperage fan to our GT Sprint... what I forgot from 40 years ago... a cheap add to performance without disturbing an original car...attached photo
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The older I get.. the faster I was....
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post #7 of 21 (permalink) Old 10-19-2017, 06:20 PM
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Are there an even number of blades on a plastic fan? On the old, aluminum, four blade Giulietta fans cutting it down to two won’t cause a balance problem. I don’t know how you’d balance a plastic fan if it has an odd number of blades.

Mike
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post #8 of 21 (permalink) Old 10-19-2017, 06:35 PM
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Are there an even number of blades on a plastic fan? On the old, aluminum, four blade Giulietta fans cutting it down to two won’t cause a balance problem. I don’t know how you’d balance a plastic fan if it has an odd number of blades.

Mike
I would imagine by reducing each blade equally.... that said I would rather remove it and add the electric fan .... I have a 190 mercedes fan sitting in a parts bin I am going to check clearances tomorrow ..

The older I get.. the faster I was....
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post #9 of 21 (permalink) Old 10-19-2017, 07:56 PM
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Quote:
It's still in the car for looks but an electric SPAL pusher now sits in front of the radiator.
Me too. The 12" SPAL in my Spider pushes a lot more air than the cheap no name 12" that I had before.

Ed Prytherch
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post #10 of 21 (permalink) Old 10-19-2017, 08:17 PM
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Alfa offered a bladeless hub for the 750 and 750/101 water pump. This was intended for racing use. I have several originals. Today, unless used for concourse, I often suggest those with the 750 and 101 1300 engines use an electric fan and use the bladeless version. I also have an Autodelta short blade fan for my GTA engine, but use the Euro type thin "flex-blade" fan for street use. The bladeless 750/101 water-pump is rebuilt, and for sale for $150.00 plus shipping.
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post #11 of 21 (permalink) Old 10-20-2017, 06:37 AM
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Neat looking unit...

The older I get.. the faster I was....
Tom
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post #12 of 21 (permalink) Old 10-20-2017, 08:36 AM
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The purpose of the GTA short fan was for racing classes where a fan was required. Like "stock-rims" or other regulations. Not only there, but the long blade, stock fan would explode at high rpm just often enough to be a concern. When it did, it would cut up the aluminum body, but worse, take out the radiator. End of race.
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post #13 of 21 (permalink) Old 10-20-2017, 11:30 AM
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Quote:
Originally Posted by Tom Frasca View Post
IMHO the original rads are ALMOST as good as any .... boiled out and flow tested no issues whatsoever....I think I am going to totally remove the fixed blade and install a low amperage fan to our GT Sprint... what I forgot from 40 years ago... a cheap add to performance without disturbing an original car...attached photo
Why?

Its a lovely original car, why are you chasing tiny amounts of hp on a stunningly original car? ... leave the fan on and enjoy your beautiful car
Pete

'71 1750 Series 2 GTV:
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post #14 of 21 (permalink) Old 10-20-2017, 05:44 PM
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Why?

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Originally Posted by PSk View Post
Why?

Its a lovely original car, why are you chasing tiny amounts of hp on a stunningly original car? ... leave the fan on and enjoy your beautiful car
Pete
Just be careful if you do keep it. The plastic becomes brittle with age. Mine disintegrated and damaged the radiator, overheating the engine.
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post #15 of 21 (permalink) Old 10-20-2017, 06:27 PM
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Plastic fans become brittle with age. They are actually a type of nylon, I believe. They are a replacement item. The support ring in front of the hub MUST be used, the bolts NOT tightened terribly tight. If you fear they will loosen with use, put a dab of silicone sealant on the threads before tightening.
If you examine blown up fans, they will fail with a blade breaking off from a nick in the edge, or come apart at the hub, from over tightened bolts. It's not a bad plan to replace the fan every 5 or 6 years, buying new from one of our good sources.
Years ago in racing, we used to boil them in a large pot of water for 15 minutes before initial installation. The thought was it stabilized stresses in the material. This came from radio controled model airplane builders that did the same with thier nylon propellers.
All the short blade GTA fans were boiled, and many are still around. Maybe boiling had a benefit.
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