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Chevy big block cylinder boring, how much?

Discussion in 'The Garage' started by madmike, Mar 4, 2003.

  1. madmike

    madmike 1/2 ton status

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    Who here has safely bored out a 396 (4.094" bore) or 402 (4.125" bore) to a 4.25", which is for 427 or 454?

    I have a factory 402 (4.125" bore), but the block casting number (3999289) indicates it is a 454 block. I am thinking (hoping) that it is a genuine 454 block that just wasn't bored out as much as it could've been from the factory. In other words, the block was cast for 454 use, but machined for 402.

    I have access to a 4" stroke forged crank for a good price, and if I can safely, reasonably, and reliably turn this into a 454, I would like too. I plan on having the cylinder walls sonic tested for thickness, but I was just wondering if any of you had any experience with this. Thanks for any insight! /forums/images/graemlins/smile.gif
     
  2. Mr.Chevy4x4

    Mr.Chevy4x4 1/2 ton status

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    I seriously doubt the cylinder walls are thick enough to go .125 over. .100 over on blocks that have been filled is very common. My suggestion would be to have it sonic tested to determine the thickness and go from there.


    Mike
     
  3. madmike

    madmike 1/2 ton status

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    C'mon peeps, chime in!
     
  4. Lonnie

    Lonnie 1/2 ton status

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    That casting number is not in my listing, but I can tell you that some early 396's (not all) were suitable to bore to the 4.25" bore. These were to the best of my knowledge, only thru the '69 model year & were all Hi-perf 4 bolt blocks with the same casting #'s as a 427. 2 of these castings are the 3855961 & also the 3937726. This is still not 100% reliable as it only took a different water jacket sand core in the casting process to change the wall thickness. I have done this with both a '65 block & a '69 block. The only way to know is to have it sonic checked. If yours is supposedly listed as a 454 casting, it is definitely a '70 or later block, so I would be skeptical.
     
  5. madmike

    madmike 1/2 ton status

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    Thanks for the response Lonnie. I do plan on having the block sonic tested, a shop said $50. I think that's reasonable.
     
  6. Brady

    Brady 1/2 ton status

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    Not positive on this but have been told the 454s have a thick wall.A guy I know has his bored .070.Should be able to go .100 on these.Brady
     

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