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Visual ques between 454 and 502, can I tell the diffrence

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Nrose07, Jun 21, 2003.

  1. Nrose07

    Nrose07 1/2 ton status

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    Looking at a 92 3/4 GMC. Dam valve covers are 502's but is the motor?
     
  2. blasterD

    blasterD 1/2 ton status

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    Externally they are identical. The quickest way I know of to tell is to pull a head and measure the bore. 454 is 4.25" 502 is 4.5" (4.47" to be exact). A stock 92 should have a gen V big block. Here are the differences between the 3 generations of Chevy big block.

    Gen IV: Mechanical fuel pump boss, 2- piece rear main seal, adjustable valvetrain.
    Gen IV is 454 only

    Gen V: No mechanical fuel pump boss, 1-piece rear main seal, non-adjustable valvetrain.
    Gen V can be either 454 or 502

    Gen VI: Mechanical fuel pump boss, one-piece rear main seal, non-adjustable valvetrain,
    Gen VI can be either 454 or 502

    You can use the valvetrain to positively identify gen IV from gen V/VI engines but that won't tell you if you have a 502 or a 454.
     
  3. big pappa b

    big pappa b 3/4 ton status

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    Actually, the quickest way would be to look at the numbers on the back of the block and compare them with this list: Big block casting numbers
     
  4. fortcollinsram

    fortcollinsram 1/2 ton status

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    or knock oput a freeze plug and check if it has siamiesed cylinder walls...if it does, it is a 502...


    Chris
     
  5. prjt_blzr

    prjt_blzr 1/2 ton status

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    Shouldn't a 92 block have 7.4L stamped on the drivers side of the block??
    Mike
     
  6. the professor

    the professor 1/2 ton status

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    The 7.4 / 454 will have "7.4L" cast on the side of the block.in front of the starter....in 2 or 3 inch high lettering.... Can't miss it...no exceptions... /forums/images/graemlins/cool.gif /forums/images/graemlins/truck.gif
     

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