Installing a 6-71, should I use a crank hub or keep my SFI balancer

Discussion in 'High Performance Modifications' started by Z-Life, Apr 7, 2021.

  1. Z-Life

    Z-Life Nasty Member

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    I have no experience setting up and running a 6-71 blower, I am reading all I can find and in the final stages of parts gathering. Have a really nice polished 6-71 with a long snout and 3" belt with pulleys setup to run it 18% under. The blower is from BDS. I expect to need to swap to a short water pump, and while I wish I could run a serpentine system Ive only seen them for LS set up and not SBC. In addition to the short w/p I will have to move the alternator and ps pump mounting back towards the motor. Im looking at a crank hub, pulleys and intake is about all I need to finish. I've read you can run either the harmonic balancer, or a blower crank hub. Cons of the balancer are only 3 mounting bolts for the pulleys and that is a weak spot that can come apart and cause a lot of damage. Crank hub has 6 bolts to mount pulleys and they never come apart. Im just concerned as there is no weight to the crank hub but people say the big blower belt will make up for the lack of a balancer.

    I guess what I am looking for is confirmation that I can run the crank hub instead of a balancer on my street application and not worry about it, someone to say yes that is how we run them all day long.

    I'll probably be running v groove pulleys and trying to add A/C at some point, serpentine would be cool but Im not willing to pay big bucks for one, if there is any factory serpentine system that would work well for this application I'd like to know what have others done.
     
  2. G72Zed

    G72Zed Veteran Member

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    I would run a damper and not the solid crank hub, maybe drag only, but the partial throttling and varying speeds and decel on a street application may be a lot to ask for a belt. Harmonics play havoc on parts.

    I'm currently (re) building a 500 inch BBC with a 8-71, it had a crank hub, needless to say, it's not going back on, got an ATI Supercharger damper with positive 6 bolt hub, dual keyway as well.

    Look into ATI for the SBC, I'm sure they have one for your application. I know the serious stuff has the BBC snout with dual keyway.
     
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  3. Z-Life

    Z-Life Nasty Member

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    Wow I see them, I didnt know. thanks man.
     
  4. Z-Life

    Z-Life Nasty Member

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    Found an old pic.I knew I had a certified dampener, was wondering if it had 6 holes...nope, looks like Im going to have a spare balancer, too bad its a nice one, and a intake/carb.
    old-engine.jpg
     
  5. 1980RS

    1980RS Veteran Member

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    Run the biggest Harmonic Balancer that you can, your crankshaft will thank you for it.
     
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  6. Lowend

    Lowend Administrator. .a car, a man, a maraca. Staff Member Lifetime Gold Member

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    THIS - I'd never run a street V8 without a harmonic balancer.
    Stay away from Fluidamper and other fluid-based units, they cause more problems than they solve
     
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  7. Z-Life

    Z-Life Nasty Member

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    Found the balancer, I guess I should not complain but it requires a BBC timing cover for the crank seal, its always something...
    https://www.summitracing.com/parts/ati-918869

    ATI Performance Products ATI918869 - ATI Super Damper Supercharged Series Harmonic Balancers
    Write the First Review

    Part Number: ATI-918869

    [​IMG]
    Image is a representation of this item.
    Actual item may vary.

    • [​IMG]
    $354.24

    ATI Super Damper Supercharged Series Harmonic Balancers

    Harmonic Balancer, Super Damper, Supercharged, Internal Balance, Steel, Black, Chevy, Small Block, Each
    See More Specifications | Check the Fit




    Only 8 left in stock - order soon
    Estimated Ship Date: Today Would you rather pick it up? Select Location
     
  8. Z-Life

    Z-Life Nasty Member

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    After balancer I was thinking a couple of these v groove pulleys, then the blower pulley. Any problems yet? Im fixing to pull the trigger and order the balancer and pulleys, will wait a little bit in case someone has a better idea.....thanks for your help.

    https://www.blowerdriveservice.com/VP-3512-CHEVY-1V-ACCESSORY-VEE-PULLEY_p_467.html

    Home > Drive Kit Components > Vee Groove Pulleys > VP-3512 CHEVY 1V ACCESSORY VEE PULLEY



    VP-3512 CHEVY 1V ACCESSORY VEE PULLEY
    Your Price: $60.00
    In Stock.
    Part Number:VP-3512
    Quantity




    Chevy Accessory Vee Groove Pulley with 1/2" center hole for crank bolt.

    It can be stack with additional BDS Vee Groove Pulleys and BDS drive spacers.

    The vee pulley is .700" wide with a diameter of 6.25". It's made with billet 6061 aluminum.

    This part is used in all BDS' Chevy Blower & Drive Kits
     
  9. Lowend

    Lowend Administrator. .a car, a man, a maraca. Staff Member Lifetime Gold Member

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  10. Zspoiler

    Zspoiler Veteran Member

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    I have a 1979 Z-28 with 377 cubic inch Weiand 142 mini blower.I used a Fluid damper. And it cracked an $800 Scat crankshaft .at the first throw.I use an 8" Chevrolet harmonic balancer and doubled keyway Scat internally balanced stroker I crankshaft. With all the hassle of pulling the engine new gaskets and the like .It was a very expensive lesson.
     
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