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Technical Piston differences

Discussion in 'The Hokey Ass Message Board' started by Fermiumhalo, Jul 11, 2014.

  1. Fermiumhalo
    Joined: Jul 27, 2007
    Posts: 156

    Fermiumhalo
    Member
    from Japan

    ImageUploadedByH.A.M.B.1405136842.736275.jpg

    ImageUploadedByH.A.M.B.1405136914.215580.jpg

    These are the same model piston, KB 118 for use in a 350 rebuild. I'm assuming there must have been a change in design at some point. All the measurements are the same except for the height of material on the top of the piston. The straight edge relief has a thicker center section dividing the rings. The dual valve reliefs design is equally spaced. anyone know if one design is newer or older? Perhaps one design is stronger than the other?


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  2. if they came together in set they were packaged incorrect!
     
  3. 1934coupe
    Joined: Feb 22, 2007
    Posts: 4,605

    1934coupe
    Member

    I don't know if it's an optical illusion but the wrist pin heights (CD) looks different. I agree they are mismatched as far as a set goes.

    Pat
     
  4. Fermiumhalo
    Joined: Jul 27, 2007
    Posts: 156

    Fermiumhalo
    Member
    from Japan

    Not the same shipment, these are 2 individual sets of pistons. The specs are the same for both but one set was made in 2006 and the valve relief cut set was made in 2012. The only difference is the top of the pistons and the space between the rings. Does anyone know if there is an advantage of the D design over the heart valve relief design?



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  5. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

  6. slowmotion
    Joined: Nov 21, 2011
    Posts: 3,276

    slowmotion
    Member

    Wonder if they cc the same. To the naked eye it appears the top one could be slightly more.
     
  7. Mike VV
    Joined: Sep 28, 2010
    Posts: 2,406

    Mike VV
    Member
    from SoCal

    If the pictures are correct...2nd picture (from side), use the pistons on the left.
    The top ring appears to be higher. This will allow more gas to be burned rather thAn wasted.

    You'd have to CC them to find out which has the higher volume.
    Top picture, the one on the right has the better quench/mixture of fuel during the initial combustion process.

    Mike
     
  8. Speed Gems
    Joined: Jul 17, 2012
    Posts: 3,399

    Speed Gems
    Member

    The one with the D shape would probably have a lower CR.
     
  9. Relic Stew
    Joined: Apr 17, 2005
    Posts: 1,142

    Relic Stew
    Member
    from Wisconsin

    I'd guess the dish was changed to match modern aftermarket heads with heart combustion chambers.

    The D-shape would be good with stock D chambers, the heart would give more quench and swirl with a heart chamber.
     
  10. Fermiumhalo
    Joined: Jul 27, 2007
    Posts: 156

    Fermiumhalo
    Member
    from Japan

    Thanks for the intel guys, I spoke with UEM the makers and the specs are the same as far as piston height and cc. The d is just an older design that was used to promote swirl but it could never be proved. Therefore in 2011 they changed the design to the heart and the tech also said the heart is a little stronger due to the design. I'm using these with 305 58cc heads on a 350 bottom end, which would you throw in it? Motor won't rev past 5500 and it's in a cruiser so daily dependability is all I'm after.



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