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Thread: Different heads on Engine

  1. #1
    I just found out that I have 2 different heads on my engine. One head has a casting number of 3964291 and the other is 3919840. They are both rectangle port heads but one is 107cc and the other is 109cc according to what I found on the net. The engine runs great but should I be concerned? Thanks

  2. #2
    UBFJ #454
    Which side are the 107's on?

  3. #3
    The 107's are on the 1,3,5,7, side.

  4. #4
    UBFJ #454
    How about milling the 109 side down so that their 107.

  5. #5
    problem will only exist if you are concerned with high performance balance. most stockers are so far out of stoiciometry that a 2pnt. difference is nothing to worry about. if you have ever ground heads you will know that 2 cc"s is not hard to get out of shape with.

  6. #6
    UBFJ #454
    I agree ... just don't like things that aren't right. Also, 109's are on the rich side.

  7. #7
    I would tend to think that no factory BBC head is balanced as far as flow goes.
    Flow to the #1,5,8,4 intake runner/cylinder is better than flow to the #3,7,6,2 on each head (think I got that right ).
    Even though it is not right, it probably will not make much of a difference if it was correct.(regarding the 2 different wise)
    Removing 2cc's out of a combustion chamber would not be that hard, and maybe even better cause the removal might better the flow around the valve (shrouded valve).
    [ December 04, 2002, 05:02 PM: Message edited by: MikeF ]

  8. #8
    I would imagine many of the castings are the same, just minor flow-characteristic changes, no?
    I say this because Holley has created many different models of carbs, but based off only "X" amount of castings.
    Just food for thought! Don't you think?

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