Custom Piston compression height

Discussion in 'Street/strip 400/430/455' started by sean Buick 76, Jul 8, 2021.

  1. sean Buick 76

    sean Buick 76 Buick Nut

    I have a friend overseas asking for help buying custom pistons. He has unknown brand flat top pistons at zero deck and he measured the compression distance to be 2.1866” however that seems high compared to the off the shelf pistons specs. He wants forged replacement pistons the same spec but 30 thou overbore I’m just trying to double check this before I help buy and ship him new custom pistons.

    in an ideal world I would have the engine here to triple check this all but it’s challenging overseas.
     
  2. Stevem

    Stevem Well-Known Member

    It would emencely help to know what cid motor we are discussing here!?
     
  3. sean Buick 76

    sean Buick 76 Buick Nut

    sorry it’s a stock stroke 455 with TA alum heads
     
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    In a zero deck engine, 1/2 the stroke + rod length + compression height =Deck height

    The stock deck height listed for a 455 is 10.57"

    So, 3.90/2 + 6.600 = 8.55

    10.57 -8.55 = 2.02" compression height

    Blocks vary somewhat, so you would need a more exact measurement for deck height, and that 10.57 doesn't count any resurfacing of the deck or align honing, so the above is all theoretical:).

    EngineSpecs.JPG
     
    Last edited: Jul 8, 2021
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  5. Jim Weise

    Jim Weise EFI/DIS 482

    Compression distance is measure by actually measuring the piston thickness from the pin hole to the top of the piston.. Then, since the distance is actually specified from the pin centerline, add half the pin diameter.. or .500 if your working with a 1" Buick Pin.

    The pistons with the largest CD that are not customs that I am aware of in the aftermarket for this engine are the KB hypers, with a CD of 2.020.

    So your going to need to tighten up that measurement spec, nothing was ever 2.1 anything.. Pistons would be hanging out of the deck.

    JW
     
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  6. sean Buick 76

    sean Buick 76 Buick Nut

    Thanks guys I will have him re measure
     
  7. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Jim can advise you about the Diamond or Autotec pistons.
     
    sean Buick 76 likes this.
  8. sean Buick 76

    sean Buick 76 Buick Nut

    Thanks will give him a call
     
  9. BrianTrick

    BrianTrick Brian Trick

    Gawd that’s a tall piston!
     
  10. sean Buick 76

    sean Buick 76 Buick Nut

    I don’t think it’s that tall. Good thing I didn’t order pistons for him based on that spec.
     
  11. BrianTrick

    BrianTrick Brian Trick

    The factory Buick 455 pistons are just naturally big tall slugs. A lot of weight at the end of the rope. Even with a stock crank,I still run a longer rod,a much shorter/lighter piston,and a modern ring stack.
     
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  12. sean Buick 76

    sean Buick 76 Buick Nut

    Agreed, I can imagine a lot of weight can be saved with a longer rod. Getting custom pistons without taking advantage of longer rods and a better ring pack seems like a waste.
     
  13. 1969RIVI

    1969RIVI Well-Known Member

    Getting custom pistons is a benefit on its own for getting to zero deck for a better running engine. Having longer rods is a bonus added to the equation. I went with custom pistons and a better ring package on my build and I'm using stock reconditioned rods and my deck was cut down to 10.55. Just my 2 cents on it anyways.
     
  14. sean Buick 76

    sean Buick 76 Buick Nut

    I had him double check and the pistons are 1.989” compression height. Does that seem to match what the TA pistons are? The website doesn’t list that spec.

    that does seem to match the math Larry did so is thanks.
     
  15. Bens99gtp

    Bens99gtp Well-Known Member

    Most shelf stk piston are 1.975-1.980. So his numbers are close enough to roll with.
     
  16. john.schaefer77

    john.schaefer77 Well-Known Member

    I thought TA's JE pistons were 2.0.
     
  17. john.schaefer77

    john.schaefer77 Well-Known Member

  18. sean Buick 76

    sean Buick 76 Buick Nut

    john.schaefer77 likes this.

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