1. moparsquid

    moparsquid FBBO Gold Member FBBO Gold Member

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    hi need some input im building a 383 its been awhile since ive done one I have a 69 HP block that was told to me it was a freash 30 over bore ,well it wasnt and it needs another 30 to true it up making 60 over is this acceptable in a 383 its going to be a flat top piston build with not a big cam will it survive on the street without over heating?
     
  2. zyzzyx

    zyzzyx FBBO Gold Member FBBO Gold Member

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    How do you know it's going to take another 0.030 to clean it up????
    0.060 would be O.K., but it leaves no room for error. Can't do anything
    more with the block after you go +0.060.
     
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    • 451Mopar

      451Mopar Well-Known Member

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      Sonic test the bore thickness.
      I'm in the same boat with a 440 that I have. It is 30 over and still has bore wear at the top. Measuring the wear, it looks like it will cleanup at 4.375 (55 over) or 4.380 (60 over), but I need to check how thick the cylinders are first.
      I think if it is less than 1/8" (0.120") at final bore size then the bore thickness is too thin? Could maybe sleeve the block if needed?
       
    • moparsquid

      moparsquid FBBO Gold Member FBBO Gold Member

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      the machine shop mic,ed the bores and the looked at the ridge and taper and determined it would take 30 thou more to true up the bore
       
    • moparsquid

      moparsquid FBBO Gold Member FBBO Gold Member

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      I was considering sleeves also but the cost ,it is a 69 hp block that came from a charger
       
    • MoparMur

      MoparMur Well-Known Member

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      From my machine shop days (30+ years ago) we would always measure the taper in the bore, double that figure, and go to the next oversize. So for example: Say you have a block that started out with a 4.000 bore size. You measure it, and it has 0.008" wear (generally found near the top of the bore). If you double that figure, that equals 0.016". So going to the next oversize would dictate you buy a 0.020" oversize piston (if available). This worked 99.9% of the time. The odd time there would be a shadow of cylinder showing that the boring/honing process wouldn't clean up, but it would be negligible. If in this case the wear was 0.009" you may be well-advised to go 0.030" over, as doubling the wear to 0.018" and moving up to 0.020" over doesn't leave much room when bringing final size to 4.020. Any other machinists out there can chime in, but this worked for us.
       
    • MoparMur

      MoparMur Well-Known Member

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      And as others have said, sonic test the block. These days machining costs are expensive, and also parts costs aren't cheap. We used to charge $64.00 to bore a block; obviously much more than that these days. Sometimes spending more money up front will save you tons down the road. Most of the old Mopar blocks I ever bored were plenty stout, but it's ALWAYS smart to know what you've got.
       
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      • bm02tj

        bm02tj Well-Known Member

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        If not the original to the car locate a 400 block they look the same on outside
         
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        • BSB67

          BSB67 Well-Known Member

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          Off the shelf 0.040" over pistons are available, are you sure they won't work.

          What is it's planned use, how important is that block to you, and what is your budget?

          For 40 years people have been boring BBM blocks 0.060" over, but now I guess its bad and shouldnt be done without a sonic check.

          If its a mild hot rod deal, you'll be fine.

          If its important to you to minimize the over bore, you need to prove to yourself what the minimum over bore is (not just take their word for it) and have a custom piston made to work with your minimum over bore.

          Get a new block, get a 400.
           
        • moparsquid

          moparsquid FBBO Gold Member FBBO Gold Member

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          i have a spare 65 383 standard bore but a piston is froze in it from sitting ,I plan on recreating a build i found in a old direct connection book for the 346 hp build that was an nhra class that ran a clay smith cam and 516 heads with dual carbs sounds fun mostly street maybe a run on the track
           
        • 66Satellite47

          66Satellite47 FBBO Gold Member FBBO Gold Member

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          IMHO, for a fairly mild build, most any 383 will take .060. As I recall 383's were noted for ability to accept a .060 overbore. But I think .040 pistons were available(custom's sure). Sonic check will give you the indication of how big the bore should be. The 516 heads will work real good with pocket porting and the larger exhaust valves.
           
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