90 over 318 Head Gasket info needed !!

Small Block Mopar Engine

  1. 1Badcolt

    1Badcolt Well-Known Member

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    Fixing to do the boring for my 318 and just have an unusual situation kinda !!!
    90 over 318 is a 4" bore and its LA block so couldn't I just order a Cometic MLS gasket for a LA 360 since it has a 4" bore and all be well ???
     
  2. prorac1

    prorac1 Well-Known Member

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    Most of the small block Chrysler head gaskets I’ve seen usually have over a 4” bore. But I’ve always used pretty common generic felpros.

    I think Jason’s on his 318 we’re felpros with a 4.08 bore.

    Hope this helps. Eric
     
  3. 1Badcolt

    1Badcolt Well-Known Member

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    Thank you Sir
     
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    • 4spdragtop

      4spdragtop FABO Gold Member FABO Gold Member

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      I have Felpro 1008 for the 340. Bore is 4.180. Buy them at dodge store under MP#, way cheap and the only way to buy in pairs. Cant remember the MP#
       
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      • Garys72Duster

        Garys72Duster Well-Known Member

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        Is .090" over on a 318 even doable? Just curious, as I have only done big blocks. We usually go .020, .040 or at the most .060, but 60 is pushin it! How much overbore will a 318 take? Is 90 the max? Thanks.
         
      • prorac1

        prorac1 Well-Known Member

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        From what I understand earlier 318 blocks can be sonic checked for wall thickness, and often bored to a 4.00 bore.
         
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        • 1Badcolt

          1Badcolt Well-Known Member

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          Shane @ Crower Cams has went beyond 90 over
          Im using a 68 model block that has been sonic tested and block will have a partial fill also.
           
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          • 1Badcolt

            1Badcolt Well-Known Member

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            I have the following
            68
            70
            (2) 1974 blocks
            They are cheap to purchase and works for me .
            My recent purchase/ project 66 Dart has a nice 70 340 in it but Im trying this format first with the 318 blocks and my custom crank with 3.20 stroke.
             
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            • Garys72Duster

              Garys72Duster Well-Known Member

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              Makes sense, I would definitely get it checked before I bored it that much. I am more and more impressed with the A engine as time goes by. Saw a Duster with a 408 run a 10.75 last summer, at 5400 feet! Wiki stated the LA engine is just a lighter version of the early A motor. So LA stands for Light A. Like 40 pounds lighter. They may not take as much of an overbore.
               
            • 1Badcolt

              1Badcolt Well-Known Member

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              Older the block normally the better this engine is going in a 66 Dart which will be run in the Super Stock division and with a Jerico.

              20160518_0621221.jpg
               
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              • Garys72Duster

                Garys72Duster Well-Known Member

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                What displacement do you end up with a 318 bored 90 over? Then adding the 3.20 stroke crank, what do you have? Is that a shorter stroke than a stock 318?
                 
              • 4spdragtop

                4spdragtop FABO Gold Member FABO Gold Member

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                • 1Badcolt

                  1Badcolt Well-Known Member

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                  Crank is special
                  Bob Glidden unit from late 1978
                  It uses small journal Chebby rods machinist is using a 6.200 H Beam and custom pistons to be ordered soon just getting started with shortblock
                  321 CI on the build
                  Super Stock class Im running in is 9.5 lbs per Cubic inch
                   
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                  • 1Badcolt

                    1Badcolt Well-Known Member

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                    • 1Badcolt

                      1Badcolt Well-Known Member

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                      20180910_163818.jpg

                      20180910_132153.jpg
                       
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                      • Garys72Duster

                        Garys72Duster Well-Known Member

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                        Summit shows those gaskets fitting all the wedge small blocks from 273 to 360, up to a 4.060 bore. Good luck with your SS engine!
                         
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                        • xLURKxDOGx

                          xLURKxDOGx "An angel fat, at satan's feast" FABO Gold Member

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                          I’ve got a steel shim 4.06 bore
                          6AD3B318-A119-4A4C-9007-B66D2DB0F65E.jpeg

                          E1CAC2C8-A1BE-4A9B-8D37-430CF289698B.jpeg

                          156D695C-F25F-4DCF-BB88-6F656927093C.jpeg
                           
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                          • 1Badcolt

                            1Badcolt Well-Known Member

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                            Thank you
                            Great info
                             
                          • 1Badcolt

                            1Badcolt Well-Known Member

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                            • skrews

                              skrews Well-Known Member

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                              Don't use a 4" bore gasket on a 4" bore block the fire ring will over hang the cylinder bore after chamfering the block to drop in the rings. I'd recommend a 4.08 gasket.
                               
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                              • 1Badcolt

                                1Badcolt Well-Known Member

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                                Thank you
                                 
                              • 4spdragtop

                                4spdragtop FABO Gold Member FABO Gold Member

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                                I'd have to chk my set, but pretty sure they are bigger bore than what summit lists...I hope so my 340 is 0.030" over lol.
                                 
                              • nm9stheham

                                nm9stheham Well-Known Member

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                                Yes, I went to 4.125" with a set of Cometics on a 340 over bored to 4.060". There will also be some small mis-registration of the chambers on the bores that will require a slightly larger gasket bore hole. So the 4.080" recommended above is the most suitable size for your use here IMHO.

                                The Cometics can be had in quite a variety of thicknesses and bore sizes too, starting at .027" thick.

                                Go here:
                                https://www.cometic.com/c-1280258-automotive-domestic-mls-head-gaskets.html
                                Then enter your engine type and it will pop up a whole list of MLS head gaskets for the LA with their whole variety of thickness and bore hole sizes.

                                Be aware that the head and block surface finishes need to be in a certain range for these MLS head gaskets. So keep that in mind. The info is somewhere on the Cometic site.
                                 
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                                • 383Scampman

                                  383Scampman Well-Known Member

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                                  I may be mistaken but I believe the early 318's (67-69) have thicker walls and forged cranks . Don't throw away those old 318's folks .
                                   
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                                  • xLURKxDOGx

                                    xLURKxDOGx "An angel fat, at satan's feast" FABO Gold Member

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                                    Looks like .32, not sure its going to compress much more than that.

                                    Jake
                                     
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