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396 vs 427

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  • Wayne M.
    Expired
    • March 1, 1980
    • 6414

    #16
    Re: 396 vs 427

    Here's a view through the freeze plug hole on a 2-bolt 396/325 hp 3855961 block; you can see the casting date. Seem to remember that the distance between the cylinder external castings allowed the insertion of a standard HB hexagonal pencil diameter.
    Attached Files

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    • Patrick B.
      Extremely Frequent Poster
      • August 31, 1985
      • 1995

      #17
      Re: 396 vs 427

      Originally posted by Wayne Midkiff (3437)
      Here's a view through the freeze plug hole on a 2-bolt 396/325 hp 3855961 block; you can see the casting date. Seem to remember that the distance between the cylinder external castings allowed the insertion of a standard HB hexagonal pencil diameter.
      I don't know if the 961 block was the same internally as a 427, but the 65 model year 962 blocks certainly were. These blocks also have the webs below the front of the intake manifold like a ZL-1 block. Around August 65, the 962 casting number was retained but the blocks lost the front webs and the thick cylinder walls and could no longer be bored for 427 pistons. It is also odd that the block design changed in visible ways but the casting number did not change for the 66 model year.

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      • Bill W.
        Extremely Frequent Poster
        • March 1, 1980
        • 2000

        #18
        Re: 396 vs 427

        Patrick I have never been able to find out why the big change it castings without changing casting numbers . I have never seen a real 65 Corvette 962 2nd design block .

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        • Wayne M.
          Expired
          • March 1, 1980
          • 6414

          #19
          Re: 396 vs 427

          Originally posted by Patrick Boyd (9110)
          I don't know if the 961 block was the same internally as a 427, but the 65 model year 962 blocks certainly were. These blocks also have the webs below the front of the intake manifold like a ZL-1 block. Around August 65, the 962 casting number was retained but the blocks lost the front webs and the thick cylinder walls.....
          Here's another shot of my 961 2-bolt, cast mid-May '65, with webs both front and back. Seem to recall 961/962 blocks with webs (following eBay listings) with casting months H (Aug) or maybe even I (Sept) of 1965, before they were eliminated.





          c

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          • Keith B.
            Very Frequent User
            • March 7, 2008
            • 928

            #20
            Re: 396 vs 427

            Wayne for what its worth I have a 961 block dated Nov 4th 1965 that does not have the casting webs

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            • Patrick B.
              Extremely Frequent Poster
              • August 31, 1985
              • 1995

              #21
              Re: 396 vs 427

              Originally posted by Wayne Midkiff (3437)
              Here's another shot of my 961 2-bolt, cast mid-May '65, with webs both front and back. Seem to recall 961/962 blocks with webs (following eBay listings) with casting months H (Aug) or maybe even I (Sept) of 1965, before they were eliminated.





              c
              Wayne -- I am not familiar with 961 blocks but yours sure has the external peculiarities of the early 962 blocks. Some books also claim that very early 66 427s used the 961 block, so it must also have the thick cylinder walls of the 65 962 block. I don't know if the claim of its use as a 66 427 have been verified. Does the 66 judging manual accept it?

              Comment

              • Carl N.
                Expired
                • April 30, 1984
                • 592

                #22
                Re: 396 vs 427

                Michael, Joe, Patrick - If memory serves, in 1970 Chevrolet increased the bore size of the 396 block to 4.125 inches thus the 402 which showed up in a lot of the Chevelles as a "396". In an article by Smokey Yunick (Hot Rod Mag December 1965) called "396 Wedge Yunick Style" Smokey details the build up of a 396 to produce 560 hp on the dyno and live at 6400 rpm for NASCAR use. The 962 block he used is bored to 4.125 inches and GM 3879928 pistons .

                Comment

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