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Thread: Frankenstein M52B25

  1. #1
    Join Date
    Jun 2018
    Location
    Central Florida
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    1
    My Cars
    98 323i vert

    Frankenstein M52B25

    So, I have a weird idea. I am getting ready to yank my M52B25 because I blew it. 25PSI from cylinder 6. I already have another engine that I’m going to toss into the car for the time being. My question is since I plan to build the B25 that’s coming out, would over boring the cylinders to 86.5mm for s52 pistons work? And on top of that, would my stock rotating assembly be able to work with it?

  2. #2
    Join Date
    Oct 2003
    Location
    Seattle
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    5,776
    My Cars
    99 M3
    You will have to check cylinder wall thickness for the bore change.
    The S52 has a longer stroke, so an S52 Crank would be required.


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  3. #3
    Join Date
    Jun 2005
    Location
    New England
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    25,402
    My Cars
    F90 M5; E36 M3 Turbo
    Obviously for bigger pistons with stock crank and stock rods you need custom pistons with different pin heights (or custom rods but no one does it that way). Buy an S52 crank and use 135 mm rods and bore to S52 piston spec and you are set. Many replacement S52 pistons come in slight overbore.

  4. #4
    Join Date
    Oct 2003
    Location
    Seattle
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    5,776
    My Cars
    99 M3
    …and generally, you should use as long of rod you can fit in any given block.

    https://www.enginebuildermag.com/201...ng-rod-ratios/


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