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Mk IV vs. Gen V BBC

Discussion in 'The Garage' started by Enginerd, Jan 8, 2007.

  1. Enginerd

    Enginerd Registered Member

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    I was fortunate to recently buy 2 complete but dissassembled 454 cores.
    One is a late 1980's Mark IV and one is 1991 Gen V block.

    Which is better to build? Parts availability is probably better for the Mk IV, but the Gen V has an improved oiling system and a one-piece rear main seal.

    I plan to use one of these to build a 496. Any opinions on which I will have better luck with?

    Thanks
     
  2. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    the gen V has redesigned waterjackets and i believe you can only use gen V heads on gen V blocks. it you put a Mark IV head on the block the jackets overlap and end up leaking coolant into the oil.

    i would use the mark IV block.
     
  3. k20

    k20 3/4 ton status

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    Mark IV all the way. The gen V has compatibility issues. You can use gen V heads on a mark IV, but not the other way around. I dont even think the gen VI heads will work on the gen V
     
  4. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Gen V and VI are compatable but you can't swap GEN V or VI heads with a Gen IV in either direction because of the coolant passages.

    I would built the Gen V engine if it were me. Gen IV stuff is what will start getting harder to find over the years and there are plenty of aftermarket Gen V and VI stuff available now.
     
  5. tiger9297

    tiger9297 1/2 ton status

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    The Gen V will have better cooling than the Mark IV. However, some of the old Mark IV heads are pretty good and can be bought cheap. If you go with the Gen V and want to upgrade the heads, you will have to go with a fairly new aftermarket head which will cost more money. If money is not a problem and you can justify a good set of Dart or AFR heads I'd go with the Gen V.
     
  6. Enginerd

    Enginerd Registered Member

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    Thanks for the replys.:bow:

    It seems as though we are pretty evenly split on the opinions about which block to use.

    Any more opinions?
     
  7. mostwanted

    mostwanted 1/2 ton status

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    not to hijack, but...................

    anyone else here of a problem with misaligned lifter journals on BBC's?
     

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