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    S52 compression questions

    I'm building an S52 (sort of) out of an M50NV and S52 rotating assembly. I noticed the piston sits ~0.032" (0.81mm) above deck, however I can't seem to find anyone else that measured this to confirm... It seems like kind of a lot. According to my math, though, it is right?

    And can anyone confirm that the deck height of these blocks is 210mm?

    89.6mm stroke / 2 + 135mm rod + 31.0mm piston comp height = 210.8

    So if deck height is really 210mm then I should be spot on.

    Then comes the issue of calculating compression ratio... I can't seem to find the volume of the dish in the piston (all of the links I find in old threads are dead) nor can I find compressed HG thickness.

    My head had to be taken down 0.013" which is 3 thou over BMW's spec (rules be damned!), which the machine shop said wouldn't be a problem. Can anyone back up this statement?

    Valve to piston clearance will obviously be checked.



    tldr:

    should the piston stick out .8mm?
    what is the piston dish volume?
    what is the compressed HG thickness?
    should I buy a new head?
    -Alex

    #2
    which the machine shop said wouldn't be a problem.
    For soccer mom car it wouldn't be a problem. But you will be revving the piss out of this engine, any removal of stock material is bad, and compensating with thicker gasket is "fix it and sell it" kind of deal.

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      #3
      I know, which is why I'm not going to use a thicker gasket. I'd rather just buy a new head. This thread is me just thinking out loud, I guess. Im going to try to use the head I have if I can, it has had some work done that I don't want to pay for twice. I will check valve to piston clearance and cut the valve pockets deeper if necessary. Thanks for your time :)
      -Alex

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        #4
        milled the head a little much....

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          #5
          doesnt sound like anything a custom gasket wouldnt fix if this was an option
          89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

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