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  1. #1
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    Default does 7 blade fan reduce hp over 5 blade

    i just installed a 7 blade fan after having 5 blade for 3 years in my 70 electra. it is a heavy car and already very prone to suuffer from as little as one more person in the car. could the extra drag of the 7 blade fan be sapping power...it feels like it but could be my imagination,marty

  2. #2
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    Default Re: does 7 blade fan reduce hp over 5 blade

    I think you are barking up the wrong tree.
    Jim Lore
    BPG 1037
    "If you cannot clear up the confusion at least make the confusion clear."

  3. #3
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    Default Re: does 7 blade fan reduce hp over 5 blade

    Yup - probably losing almost upwards of one-tenth horsepower with that combination versus the 5 blade job. You could probably make that up by avoiding one cup of Cheerios every week for your life.
    BadBrad
    '70 GS455 - Power Brute Super T10 4spd
    ex. '70 GSX
    New Project: 2000 Mercury Grand Marquis - for the kids to drive.
    New Muscle: 2013 Ford Taurus SHO - Twin Turbo Terror

    Spare 455 on the stand, just in case!


    Slideshow of BadBrad's Car: http://s517.photobucket.com/albums/u...view=slideshow

  4. #4
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    Default Re: does 7 blade fan reduce hp over 5 blade

    Your car should have a fan clutch so there is no direct connection to the fan unless the temp is high enough to make the fan kick in. Maybe you bumped or turned the distributor when changing your fan. Those big torque monster shouldn't feel any different with one passenger in. We are not all wise asses on here

    Bob H.
    1953 Buick 455 TA Aluminum SE Stg2 Heads, B4B Intake, S/P Turbo 400, Gear Vendor, 3.42 Posi. A/C
    1970 GS Project Getting close.

  5. #5
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    Default Re: does 7 blade fan reduce hp over 5 blade

    Quote Originally Posted by BadBrad View Post
    Yup - probably losing almost upwards of one-tenth horsepower with that combination versus the 5 blade job. You could probably make that up by avoiding one cup of Cheerios every week for your life.
    i see now as i changed to honeynut at the same time

  6. #6
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    Default Re: does 7 blade fan reduce hp over 5 blade

    Quote Originally Posted by rmstg2 View Post
    Your car should have a fan clutch so there is no direct connection to the fan unless the temp is high enough to make the fan kick in. Maybe you bumped or turned the distributor when changing your fan. Those big torque monster shouldn't feel any different with one passenger in. We are not all wise asses on here

    Bob H.

    i should qualify that the extra person weighs 340...

  7. #7
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    Default Re: does 7 blade fan reduce hp over 5 blade

    Quote Originally Posted by BadBrad View Post
    Yup - probably losing almost upwards of one-tenth horsepower with that combination versus the 5 blade job. You could probably make that up by avoiding one cup of Cheerios every week for your life.

    the nice part about asking dumb questions is you get very good at laughing at yourself..marty..hmm let me see they used to say after you waxed your car you went faster.....

  8. #8
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    Default Re: does 7 blade fan reduce hp over 5 blade

    .....mmmmm...forbidden honeynut Cheerios....
    BadBrad
    '70 GS455 - Power Brute Super T10 4spd
    ex. '70 GSX
    New Project: 2000 Mercury Grand Marquis - for the kids to drive.
    New Muscle: 2013 Ford Taurus SHO - Twin Turbo Terror

    Spare 455 on the stand, just in case!


    Slideshow of BadBrad's Car: http://s517.photobucket.com/albums/u...view=slideshow

  9. #9
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    Default Re: does 7 blade fan reduce hp over 5 blade

    The smaller 7 blad will not be as efficient as the bigger 5 blade the big cars in 70 were disigned to run with. The gap between the blades and the shroud is too great. You caused yourself extra work for no gain.
    Dave, Seeing Yellow
    71 GS Stage-1 Now Sold.

    Now have real 70 GSX 4 Speed QQ

  10. #10
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    Default Re: does 7 blade fan reduce hp over 5 blade

    100 pounds equals 1/10th on the quarter mile. If you put someone in the car that weights in at 350 than you're car is .35 seconds slower in a quarter mile sprint. That's not very noticable unless you've very familiar with your cars performance.

    Could just be the switch from summer to winter blend on the gas.

  11. #11
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    Default What's the best for BB Buick? (Re: 7 blade fan vs 5 blade)

    Dear V-8 Buick fans . . . .

    (of the hot air and other variety) . . .

    Quote Originally Posted by BadBrad View Post
    .....mmmmm...forbidden honeynut Cheerios....
    What's the matta with you guys - I have either eggs or pastries for breakfast like God intended!!

    Quote Originally Posted by copperheadgs1 View Post
    The smaller 7 blad will not be as efficient as the bigger 5 blade the big cars in 70 were disigned to run with. The gap between the blades and the shroud is too great. You caused yourself extra work for no gain.
    However, I'm about to play pirate and try to hijack this thread. Jim Weise is building for me a yummy 448 big-block Buick for my trusty wagon. I figured I could trust the local "fellers" to pick out a fan for this beast and they were planning to have a California boy whip up for me a 7-blade fan to keep my engine well chilled.

    Is that a bad idea? Should I be stubborn and tell them to stick with a fan designed around the time of the big-block Buick engine? Somehow this has to fit into the fan shroud of a 65 Special/Skylark.

    Anyone got some hot air to blow on this topic?

    Cheers, Edouard
    Caretaker of a 1965 Buick Special "Billy-goat"

    Read more about: The grand adventures of a trusty "billy-goat" wagon
    More photos at Biquette's stall in the V-8 Buick garage


  12. #12
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    Default Re: does 7 blade fan reduce hp over 5 blade

    Quote Originally Posted by copperheadgs1 View Post
    The smaller 7 blad will not be as efficient as the bigger 5 blade the big cars in 70 were disigned to run with. The gap between the blades and the shroud is too great. You caused yourself extra work for no gain.
    i dont understand,the 7 blade is 19.5 in like the 5 blade

  13. #13
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    Default Re: does 7 blade fan reduce hp over 5 blade

    I would tend to think that the factory engineers knew what they were doing... when you order a ''heavy duty'' cooling system [like a emergency vehicle has in it] most, most of the time , it comes with a 7 blade fan.... I had several that were on the southern sold 66 rivs that I had a while back, but sold them all.... 7 blades, thick aluminum blades , steel center, all factory.....
    That is why a police car, ambulance, ect. can sit, idleing for long periods of time, and not run hot....
    Doc "Widely unknown"

  14. #14
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    Default Re: does 7 blade fan reduce hp over 5 blade

    Big block Electras in 70 came with the same 5 blade with AC and/or heavy cooling. What did the 19.5 7 blade come from? The 7 blade in 70 was smaller.
    Dave, Seeing Yellow
    71 GS Stage-1 Now Sold.

    Now have real 70 GSX 4 Speed QQ

  15. #15
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    Default Re: does 7 blade fan reduce hp over 5 blade

    Quote Originally Posted by copperheadgs1 View Post
    Big block Electras in 70 came with the same 5 blade with AC and/or heavy cooling. What did the 19.5 7 blade come from? The 7 blade in 70 was smaller.
    im very intersted in this. you say the 7blade fan was smaller like say 18inch as opposed to my 5 blade which is 19.5 inch. my shroud is 22 inches in diameter..how would that play as maybe i should have put in a smaller 7 blade as you say,thanks marty

  16. #16
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    Default Re: does 7 blade fan reduce hp over 5 blade

    Flex-a-lite #5720 is a 20" 7 blade, clutch driven fan (aluminum blades).
    Auto Zone sells these under a different name at $20 bucks!

    A thermostatic fan clutch is limited by torque. So a 7 blade fan will flow more air in city trafic at low speed, yet use no extra power at high speeds. Same goes for larger diameter fans.
    Use a standard or heavy duty clutch. don't use the super duty clutch.

    ................HERE IS AN OLD POST OF MINE..........................

    Gary Bohannon Status: Online
    Registered User Join Date: Apr 2004
    Location: Bloomfield, MO
    Posts: 901

    Re: How much of a drag on HP?

    --------------------------------------------------------------------------------
    DON'T THROW AWAY YOUR FANS JUST YET.
    I Just found a CAR CRAFT article from May 2000. "Fan power test" at 6300 RPM on a small block Chevy.

    1. Electric fan only - 494 HP at 6300 rpm
    2. Thermal clutch fan - 487 HP (-7 hp) standard duty with spring
    3. Viscous clutch fan - 485 HP (-9 hp) no thermostatic spring
    4. HD thermal clutch fan - 478 HP (-16 hp) with spring
    5. H-Perf 6 blade flex fan - 476 HP (-18 hp) NO CLUTCH
    6. Flex a lite #1018 flex fan - 466 HP (-28 hp) NO CLUTCH
    7. Flex a lite #418 Plastic fan - 460 HP (-34 hp) NO CLUTCH
    8. Factory fixed 6 blade fan - 449 HP (-45 hp) NO CLUTCH

    Average HP at 3500 to 5000
    1. Electric only - 312.7 hp
    2. Thermal clutch - 311.6 hp (-1.1 hp) ...YES, that is ONE HP and one tenth!
    3. Viscous clutch - 306.8 hp (-5.9 hp) ...and using 6 blade factory style clutch fan blades.
    4. HD Thermal clutch - 303.3 (-9.4 hp)

    OK you get the idea here. The high torque/low rpm BBBuick will be less affected than a SBC engine. No need to throw away those fans till you start winding 6300 and over.
    GSCA # 116
    67 GS 455

  17. #17
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    Default Re: does 7 blade fan reduce hp over 5 blade

    You shroud is designed to work with the bigger 5 blad fan. A smaller fan will not allow as much air to be moved
    Dave, Seeing Yellow
    71 GS Stage-1 Now Sold.

    Now have real 70 GSX 4 Speed QQ

  18. #18
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    Default Re: does 7 blade fan reduce hp over 5 blade

    Quote Originally Posted by Gary Bohannon View Post
    Flex-a-lite #5720 is a 20" 7 blade, clutch driven fan (aluminum blades).
    Auto Zone sells these under a different name at $20 bucks!

    A thermostatic fan clutch is limited by torque. So a 7 blade fan will flow more air in city trafic at low speed, yet use no extra power at high speeds. Same goes for larger diameter fans.
    Use a standard or heavy duty clutch. don't use the super duty clutch.

    ................HERE IS AN OLD POST OF MINE..........................

    Gary Bohannon Status: Online
    Registered User Join Date: Apr 2004
    Location: Bloomfield, MO
    Posts: 901

    Re: How much of a drag on HP?

    --------------------------------------------------------------------------------
    DON'T THROW AWAY YOUR FANS JUST YET.
    I Just found a CAR CRAFT article from May 2000. "Fan power test" at 6300 RPM on a small block Chevy.

    1. Electric fan only - 494 HP at 6300 rpm
    2. Thermal clutch fan - 487 HP (-7 hp) standard duty with spring
    3. Viscous clutch fan - 485 HP (-9 hp) no thermostatic spring
    4. HD thermal clutch fan - 478 HP (-16 hp) with spring
    5. H-Perf 6 blade flex fan - 476 HP (-18 hp) NO CLUTCH
    6. Flex a lite #1018 flex fan - 466 HP (-28 hp) NO CLUTCH
    7. Flex a lite #418 Plastic fan - 460 HP (-34 hp) NO CLUTCH
    8. Factory fixed 6 blade fan - 449 HP (-45 hp) NO CLUTCH

    Average HP at 3500 to 5000
    1. Electric only - 312.7 hp
    2. Thermal clutch - 311.6 hp (-1.1 hp) ...YES, that is ONE HP and one tenth!
    3. Viscous clutch - 306.8 hp (-5.9 hp) ...and using 6 blade factory style clutch fan blades.
    4. HD Thermal clutch - 303.3 (-9.4 hp)

    OK you get the idea here. The high torque/low rpm BBBuick will be less affected than a SBC engine. No need to throw away those fans till you start winding 6300 and over.

    AHA SO i am not as stupiid as i look. any info on 7 vs 5 , thanks marty....ie do you think i could be feeling the extra draw of a 7 vs 5 blade at 415 hp 2 to 3000 rpm or losing hp with the 7 blade

  19. #19
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    Default Re: does 7 blade fan reduce hp over 5 blade

    To move more air the fan needs to catch more air. That means more wind resistance at full speed. The fan size, number of blades, and blade pitch should be enough to keep the vehicle cool while idling on a hot day. Any more than that is just creating unneeded drag on the engine.

    If you're worried about getting the most power at full throttle than switch to a viscous clutch that is designed to release at an rpm below where you like to run so that the fan is disengaged at those rpms. A thermal clutch may remain engaged at speed if the temps are high enough and that creates drag.

    Of course if you actually care about the engine and tend to use it on the street stop worrying about a few hp and make sure that the entire cooling system is designed to provide the amount of cooling the engine needs, even if it means losing a few numbers on a dyno.

  20. #20
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    Default Re: does 7 blade fan reduce hp over 5 blade

    Clutch fans with 7 blades should not loose more power, they just reach their torque and rpm limit sooner than a 5 blade.

    Thermostatic clutches will roar on start up, but they will back off little as the engine is warming up. After warm up, they will pull harder if engine temp gets too high. When that happens, It's time to stop hammering the throttle or you can detonate the engine.
    GSCA # 116
    67 GS 455

  21. #21
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    Default Re: does 7 blade fan reduce hp over 5 blade

    It's basic aerodynamics: If the fan is moving more air, it will absorb more power. This is not necessarily a direct function of the number of blades. It would take into account the airfoil of the blades, the length of same, and especially the pitch of the blades. The closer that the blades fit the shroud, the more efficient the fan. Although not likely to be an issue with relatively small automotive cooling fans, excessive blade tip velocity can become an issue at higher fan speeds. Even something as simple as a fan can take a bit of engineering.
    John Codman
    Formerly owned Buicks:
    '33,'48, '51, '52, '54, '55 (3), '56, '60 LeSabre 3 sp stick.
    264 powered '53 Mercury
    322 then 264 powered 55 Ford
    264 powered '56 Chevy
    Presently - 431 nailhead powered '82 C-10

  22. #22
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    Default Re: does 7 blade fan reduce hp over 5 blade

    I wonder why wee don't balance our propellors
    Alan W

    BPG # 1048 - Charter Member
    NE GS/GN Club - 17 Year Member
    68/69 Buick StepChild Nation - 29 Year Member

    What is a Buick StepChild ?
    Quote Originally Posted by 442w30 View Post
    ... They have awkward proportions from certain angles, and they look dumpy compared to their GM brethren
    ....'68 SportWagon400 "Sportn'Wood"..............'69 GS400 Convert "BigRed"..........

  23. #23
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    Default Re: does 7 blade fan reduce hp over 5 blade

    Quote Originally Posted by 69GS400s View Post
    I wonder why wee don't balance our propellors
    We do. The three-blade McCauley prop on my Comanche was dynamically balanced with a Chadwick electronic balancer. It was damn close from the factory.
    John Codman
    Formerly owned Buicks:
    '33,'48, '51, '52, '54, '55 (3), '56, '60 LeSabre 3 sp stick.
    264 powered '53 Mercury
    322 then 264 powered 55 Ford
    264 powered '56 Chevy
    Presently - 431 nailhead powered '82 C-10

  24. #24
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    Default Re: does 7 blade fan reduce hp over 5 blade

    Quote Originally Posted by John Codman View Post
    We do. The three-blade McCauley prop on my Comanche was dynamically balanced with a Chadwick electronic balancer. It was damn close from the factory.
    I was talking about the one hanging off our water pumps - you would think that with the bearing a weak point as it is, balancing the fan would be thought about

    ... am well aware about balancing aviation props
    Alan W

    BPG # 1048 - Charter Member
    NE GS/GN Club - 17 Year Member
    68/69 Buick StepChild Nation - 29 Year Member

    What is a Buick StepChild ?
    Quote Originally Posted by 442w30 View Post
    ... They have awkward proportions from certain angles, and they look dumpy compared to their GM brethren
    ....'68 SportWagon400 "Sportn'Wood"..............'69 GS400 Convert "BigRed"..........

  25. #25
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    Default Re: does 7 blade fan reduce hp over 5 blade

    Quote Originally Posted by Gary Bohannon View Post
    Flex-a-lite #5720 is a 20" 7 blade, clutch driven fan (aluminum blades).
    Auto Zone sells these under a different name at $20 bucks!

    A thermostatic fan clutch is limited by torque. So a 7 blade fan will flow more air in city trafic at low speed, yet use no extra power at high speeds. Same goes for larger diameter fans.
    Use a standard or heavy duty clutch. don't use the super duty clutch.

    ................HERE IS AN OLD POST OF MINE..........................

    Gary Bohannon Status: Online
    Registered User Join Date: Apr 2004
    Location: Bloomfield, MO
    Posts: 901

    Re: How much of a drag on HP?

    --------------------------------------------------------------------------------
    DON'T THROW AWAY YOUR FANS JUST YET.
    I Just found a CAR CRAFT article from May 2000. "Fan power test" at 6300 RPM on a small block Chevy.

    1. Electric fan only - 494 HP at 6300 rpm
    2. Thermal clutch fan - 487 HP (-7 hp) standard duty with spring
    3. Viscous clutch fan - 485 HP (-9 hp) no thermostatic spring
    4. HD thermal clutch fan - 478 HP (-16 hp) with spring
    5. H-Perf 6 blade flex fan - 476 HP (-18 hp) NO CLUTCH
    6. Flex a lite #1018 flex fan - 466 HP (-28 hp) NO CLUTCH
    7. Flex a lite #418 Plastic fan - 460 HP (-34 hp) NO CLUTCH
    8. Factory fixed 6 blade fan - 449 HP (-45 hp) NO CLUTCH

    Average HP at 3500 to 5000
    1. Electric only - 312.7 hp
    2. Thermal clutch - 311.6 hp (-1.1 hp) ...YES, that is ONE HP and one tenth!
    3. Viscous clutch - 306.8 hp (-5.9 hp) ...and using 6 blade factory style clutch fan blades.
    4. HD Thermal clutch - 303.3 (-9.4 hp)

    OK you get the idea here. The high torque/low rpm BBBuick will be less affected than a SBC engine. No need to throw away those fans till you start winding 6300 and over.
    Yes, but the power for the electric fan comes from the alternator. There's no free lunch (power is power, electrical or mechanical), so how did those Car Crafters get around that? Maybe they just used a battery on the dyno? I can see where, for instance, a shot down the strip won't engage the electric fan, but for us city boys, the power still gets drawn off...and then there's conversion loss, to make it worse.
    '68 Buick Skylark California GS
    '00 Chevy Astro Van
    '70 Chevy 3/4 Ton Longhorn Custom Camper, numbers matching

 

 
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