Understanding Core Shift in the 455 block- why sonic checking is so important.

Discussion in 'Street/strip 400/430/455' started by Jim Weise, Feb 14, 2009.

  1. Bluzilla

    Bluzilla a.k.a. "THE DOCTOR"

    I have a Dakota Ultrasonics PR-82 that has a curved transducer. It conforms extremely well to the cylinder walls. It's the larger one in the picture. It doesn't look curved but it is. I use ultrasound gel, it's a bit pricey but works great. This unit will repeat thickness measurements after calibrating time and time again, ..... I love it.

    [​IMG]

    Larry
     
  2. Jim Weise

    Jim Weise EFI/DIS 482

    Rear pin side of number 6... always the thinnest for some reason, big or small block.

    Nice thickness overall, but that .114 center measurement just passes muster.. I set aside anything less than .100 before boring on the pin sides, for a sleeve.

    JW
     
  3. GRNDNL

    GRNDNL Wannabe

    How much is a sonic tester?
     
  4. Jim Weise

    Jim Weise EFI/DIS 482

    Keith,
    From $400 to past 2K depending on brand, features ect. The big dollar ones have built in memories and sweep readings, where you just swipe the probe down the side, and it builds a picture of the wall from top to bottom. Then interfaces with your computer and creates a report on the block.. slick, I would like to have one when I upgrade...I think I paid about $700 for my current unit, maybe 8 years ago. Figured it would pay for itself, since I was paying to have every block checked. It has.

    JW
     
  5. Bluzilla

    Bluzilla a.k.a. "THE DOCTOR"

    My Dakota Ultrasonics PR-82 sells for $1125.00, though I bought mine used in like new condition from a member for less. Like Jim said, .... if you are paying to have multiple blocks tested and plan on continuing to test, then buying one makes good sense.

    Larry
     
  6. sean Buick 76

    sean Buick 76 Buick Nut

    Jim, based on that 0.114 test (on the 350) would you advise anything over a 60 thou overbore or do you think it is good to go larger?

    I just overbore them all 30 thou and skip the sonic testing... I figure more meat (strength) in the bores is WAY better than a slight overbore advantage.
     
    8ad-f85 likes this.
  7. Mart

    Mart Gold level member

    Sean, those readings are at .030 over. Block will just get a light hone.
     
    Last edited: Jan 28, 2018
  8. sean Buick 76

    sean Buick 76 Buick Nut

  9. Gallagher

    Gallagher Founders Club Member

    Isn’t .100” getting a bit thin?
    At what point do the cylinders start to have ring sealing issues?
    Is it a certain power level, RPM, compression ratio?
     
    8ad-f85 likes this.
  10. Mart

    Mart Gold level member

    Cutting the deck thin to win may only apply playing poker!:D
     
  11. Jim Weise

    Jim Weise EFI/DIS 482

    If I saw that sonic test in a 455, I would set that block aside for a no more than 450 HP engine, and then we would move the holes around during the process, and do the minimum overbore to clean it up, and would change the size on my AutoTec or Diamond pistons to account for that. I have a small pile of blocks have been set aside for exactly this reason. Core supply is still reasonable, and typically the next one I check is thicker, and suitible for the standard .038 overbore.

    I would not bore that 350 block any more, unless your going to limit the rpm to about 5500. Even then, I would sleeve that hole, it's a good thing it's at size now for his build.

    JW
     
  12. sean Buick 76

    sean Buick 76 Buick Nut

    Thanks for the information Jim it is always nice to learn from you.
     
  13. Mart

    Mart Gold level member

    Oh boy, Now I'm looking into either block fill or a new core, sheesh!:D
     
    300sbb_overkill likes this.
  14. Mart

    Mart Gold level member

    With bore spacing on the 350 at 4.240, if you figure .100 water passage space between cyls., in a perfect no core shift blk., that ends up at .170 thickness on pin side.
    At .030 overbore (pretty std. rebuild), you would be at .155 thickness on wrist pin walls. .060 over = .130

    Only .050 of core shift would give you the readings I checked on my SB blk.

    Think we need an x-ray machine!:D
     
  15. 8ad-f85

    8ad-f85 Well-Known Member

    You'll have to machine 8 thick sleeves and silver solder them to a dry deck, siamesed except for a few air bleeds then furnace braze the bottoms in place after it's set in. Kinda like a dry deck diesel but more solid. Or skip the dry deck and braze it all in.
     
  16. sean Buick 76

    sean Buick 76 Buick Nut

    Or just keep the bore to 30 thou and skip all the hassle
     
    8ad-f85 likes this.
  17. patwhac

    patwhac Well-Known Member

    Has anyone had any experience with the cheaper sonic testers ($100 - $300) that you can now find on eBay and similar places? Most of them don't come with a curved transducer, but the price is appealing!
     
  18. BennyK81

    BennyK81 Well-Known Member

    Where do you take the three measurements?
    where the rings travel or on the whole bore length?
     
  19. piston1

    piston1 Well-Known Member

    This was disappointing! Sonic check of 2nd block in progress now.
     

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