1. Dan the man

    Dan the man Well-Known Member

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    There's a lot mention about the magnum engines being good for a budget build. So I started to do research on them and one issue that arises often is that the magnum blocks should be limited to a maximum over bore of 0.020" because of the block's being a thin wall casting, is this fact or fiction? I thought I read somewhere that the block's have a thin cylinder wall in order to save weight, that little bit of metal isn't going to save that much weight. If I was asked to design a engine I would have it to run as cool with a 0.060" over bore as with a standard bore size.
     
  2. 273

    273 Well-Known Member

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    The main advantage is you can find good shape running Magnum fairly easy and they have a bit more cr and the stock magnum head responded well to cam 4bbl and headers. Once you start talking rebuilding the advantages start going away any 360 becomes a good candidate especially if hydraulic roller cam ain't a requirement.

    I've heard of the 0.20" overbore limit never heard of anyone having a problem doing the standard 0.30-0.040" overbore.
     
  3. dodge71demon

    dodge71demon Well-Known Member

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    Mine has 040 never any problems in close to stock form
     
  4. rumblefish360

    rumblefish360 I have escaped the evil Empire State! FABO Gold Member

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    MoPar said the same things about there LA blocks.
    A sonic check solves all mysteries.
     
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    • 12many

      12many Well-Known Member

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      Both Blueprint and ATK stoker motors (long and short blocks) all show being .040” over Magnum block based. I’ve always wondered why they all bore to .040” as a standard instead of the typical .030” I can’t see used Magnum block cores being that bad as to need .040” to clean up. Maybe they get better pricing on the KB or Icon pistons in .040”? I don’t recall ever reading anywhere in their literature that the blocks are sonic checked either. Who really knows what is a magnum blocks overbore limit?
       
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      • rumblefish360

        rumblefish360 I have escaped the evil Empire State! FABO Gold Member

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        Same bore size as a stock 340. That might have something to do with it.
         
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        • 273

          273 Well-Known Member

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          Probably cause the odd cylinder might need a 0.040" it's just easier $$$ to use the same kit when you mass produce.
           
        • JunkyJimmy

          JunkyJimmy FABO Gold Member FABO Gold Member

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          I have never sonic checked one but know of a guy that had 2 mags done. He said they
          were more consistant and better than the la. The D.C. Bible had a lot of wives tales about thin wall stuff that was debunked by I believe 440 source on big blocks. I do know magnums decks are flat and equal ,front to back and side to side on all the ones I checked. The magnum oil feeds to the mains are also right at 9/32, you won't get nothing out with your bit but I check them anyway.
          The 5.9 blocks I have weighed are right at 10lbs heavier than a 360, crank sensor, and 3 to 5 more engine mounting lugs on each side, taller lifter bore casting. I am not sure if the actual bore has more meat or not. I have only seen one 5.9 that needed bored, it had a burned exh valve and must of been driven that way for awhile, most always they are in really good shape for a used engine.
           
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          • Kern Dog

            Kern Dog I like girls that wiggle FABO Gold Member

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            Larry Shephard and a few others that wrote in the Mopar books about "Thin Wall" engines were either liars or idiots.
             
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