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BBC guys, need help with differences between Gen V and VI blocks...

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by fortcollinsram, Oct 6, 2002.

  1. fortcollinsram

    fortcollinsram 1/2 ton status

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    What are the difference between the Gen V and Gen VI BBC's and what were the production years for both...Thanks gang...

    Chris
     
  2. Thunder

    Thunder 3/4 ton status

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    I'm streching my memory cells a bit but I think The Mark V and VIs both came out in 1970
    The mark Vs put out something like 350 hp
    The mark VIs were around 425 Hp
    Both engines put out around 450- 500 ft lbs of torque.
    Chevy also made a Mark IV with300 Hp( prolly a Calif. engine) around that time too.
     
  3. fortcollinsram

    fortcollinsram 1/2 ton status

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    So do the "Mark" and "Gen" designate the same thing?

    Chris
     
  4. thatK30guy

    thatK30guy 1 ton status Premium Member

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    Mark was the actual name for these motors. Gen (short for Generation) was the nickname for them. Both names are good to go.

    You cannot interchange parts from one gen to the other. Water passages are different especially in the heads where they bolt to the block.

    The intake manifolds are also different. They will not interchange between the IV and V motors.

    There are some other small stuff that make them different and non-swappable, but I would need to check my books.

    Off the top of my head, I think the Gen IV motors last year of production was '90 or '91. Gen V took over from there.
     
  5. 77fixer

    77fixer 1/2 ton status

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    So I can't use the L29 vortec heads on a MKIV BBC? /forums/images/graemlins/frown.gif
     
  6. fortcollinsram

    fortcollinsram 1/2 ton status

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    Is there a difference in the valvetrain? I was reading somewhere that the GenVI motors didn't have adjustable rockers...I will look for the article...
     
  7. fortcollinsram

    fortcollinsram 1/2 ton status

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    Okay in the November '02 issue of Chevy High Performance, in thir article about hopping up the 454 HO crate motor, they say...

    </font><blockquote><font class="small">In reply to:</font><hr />
    Since our FrankenRat 454 H.O. is a Gen VI engine, it also utilizes a net-lash rocker system that does not allow the valvetrain to be adjusted. The system differs from the typical small- or big-block adjustable rocker with a bolt that runs down through the rocker and tightens against the head.

    [/ QUOTE ]

    So how long have these blocks been in production?

    Thanks gang...

    Chris
     
  8. 77fixer

    77fixer 1/2 ton status

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    The Nov 02 issue of Chevy Hi Performance has an article where they bolt in adjustable rockers for their FrankenRat.
     
  9. 77fixer

    77fixer 1/2 ton status

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    I was too slow to grab the mag. /forums/images/graemlins/smile.gif
    Crane makes the kit to bolt in the adjustable rockers.
     
  10. nvrenuf

    nvrenuf NONE shall pass! Premium Member

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    A Gen V does not have adjustable valvetrain, I was thinking that the Gen VI went back to adjustable - not sure about the Gen VI stuff.

    The Gen V does not have a provision for a mech fuel pump, I'm pretty sure that came back on the Gen VI.

    Mr. Gasket makes special head gaskets to allow Gen IV head installation on a Gen V.

    If I remember correctly the Gen VI has more (*not a lot*) in common with the Gen IV than the Gen V. The Gen V is a design with a short production span, I'm not saying they're bad but if you have a choice for this reason you may want to get a Gen IV or VI.

    Go to a Chevy dealer parts dept and get a book called a "Power Book". This is a book produced by Chevy and it will have very detailed about the info about the current and maybe the older designs.
     
  11. Donovan

    Donovan 1/2 ton status

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