How much would this increase compression?

Discussion in 'Engine Topic' started by Ryan 79, Aug 7, 2006.

  1. Ryan 79

    Ryan 79 Veteran Member Lifetime Gold Member

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    Mar 29, 1999
    Granite Falls, WA
    How many points would a 100 CC head on a stock compression 76 454 raise compression versus a stock set of 781's?
     
  2. theflash

    theflash Veteran Member Lifetime Gold Member

    11,005
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    Feb 27, 2004
    Podunk, CT
    Depends on how many cc's the 781's are. I have 100cc heads on my 454 with a 10cc dome piston, and I'm making about 10-1
     
  3. Ryan 79

    Ryan 79 Veteran Member Lifetime Gold Member

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    Mar 29, 1999
    Granite Falls, WA
    IIRC, I think the 781s are 119 cc
     
  4. pdq67

    pdq67 BANNED

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    Jul 26, 2001
    Columbia, MO, USA
    Probably from their terribly low CR that's like 7.9 to maybe 8 to 1 even tho they are supposed to be 8.5 to like 9.75 or so?

    Using a cast-iron head like an old -206 and .020" steel shim headgaskets, imho....

    pdq67
     
  5. ZS10

    ZS10 Moderator Staff Member Lifetime Gold Member

    12,165
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    Jan 18, 2003
    BC, Canada
    Look at a piston application chart.
    You won't quite get a full point increase, maybe .7
    A +.03 454 goes from 8.2 to 8.9 with a 12cc smaller chamber 124cc to 112cc.

    You may drop 8-10cc with that swap.
     
  6. rustbucket79

    rustbucket79 Veteran Member

    Your static compression will end up at about 8.25:1 with composite gaskets, more with steel shims. (a common choice from the factory in the early 80's, 70's, etc) Not a bad swap with the correct cam, intake and headers.

    As a side note, I did that swap using 366 truck heads on my 81 1 ton 4x4, including going up to the 2.06/1.725 valves, bowl work, etc. Still a slug due to the small propane system on the truck and stock exhaust manifolds, and my 04 extra cab long box with the 6L will KILL it while getting considerably better mileage. (and comfort) ;)
     

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