440 piston compresson height question

Big Block A body Tech

  1. 69B-Cuda

    69B-Cuda Well-Known Member

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    this may be a stupid question but, here goes.....
    I have a 440 with KB 1276 pistons in it now. The "compression distance" is listed at 1.912 in.
    If I were to replace those with KB 1263 pistons (listed comp dist. on those is 1.969 in.) I am assuming that would bump my compression up a bit.. My question is, would the bit taller pistons be a noticeable change If I do nothing else to my engine? (I have no idea what cam is in it, it came out of a motorhome originally, then was supposedly in a monster jeep, and now in my Barracuda)

    engine is .030 over, I did a gasket match and ported the heads a bit, edelbrock performer intake, not much else done to it though.
     
  2. moper

    moper Well-Known Member

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    You are effectively losing .057" of combustion chamber volume - so yes - it will be an increase on the order of 1 point. But - you will have to re-balance the assembly as they will be heavier. So there has to be other work beyond pressing off and installing the new pistons on the rods. Assuming you have stock rebuild - you can get almost the same gain by replacing the stock type head gaskets with the MP steel shims for no expense but time and gaskets.
     
  3. 69B-Cuda

    69B-Cuda Well-Known Member

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    Thanks, I am aware of the work and needing to have it balanced, and I already have the MP steel shim gaskets in it. By an increase of one point, do you mean like going from 8:1 to 8.1:1 or from 8:1 to 9:1?
     
  4. bOb shingler

    bOb shingler Well-Known Member

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    one point is 1.0 so at 8.1 it'd go to 9.1 as you stated. do both, new steel shim and pistons for a 2.0 increase.
     
  5. 69B-Cuda

    69B-Cuda Well-Known Member

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    Bob, I already have the steel shim gaskets in it now..... reading, it looks like 1 point is ~4% increase in HP.... not sure about torque... so, if the 440 is putting out 350hp, it would be a ~14hp increase. If 400 HP, then ~16hp increase... If I do that, I may need to look at swapping out the cam. I have a used purple shaft I got with another 440, but I have no idea what the specs are on it or how to tell if it is OK. None of the lobes look burned or flat...

    Thanks guys!
     
  6. moper

    moper Well-Known Member

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    It's probably closer to 7.5:1 now unless the heads and or block had some blueprinting or milling work done. You'd be better served to just repalce the cam and valve springs. You'll gain more for less investment. just keep it conservative.
     
  7. ir3333

    ir3333 Well-Known Member

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    read the current post in the performance forum "dyno testing a stock '72 440"
    this will answer some of your questions.
     
  8. 80fbody

    80fbody Well-Known Member

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    You could also pull the heads and have them shaved for $100 or so and accomplish the same thing.
     
  9. 69B-Cuda

    69B-Cuda Well-Known Member

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    just read that thread... great info! Thanks, ir333!!
     
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