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Calculating Compression on 350

Discussion in 'The Garage' started by Blazer_Boy, Jul 5, 2002.

  1. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Does anyone know what the piston to deck clearance is on the 345np piston for the 350 chevy? Its pretty much the generic cast 350 piston used in several rebuild kits. Federal-Mogul makes them, I've also seen them sold as Sterling, Speed-Pro, and Sealed Power, all the same company. The amount of valve relief would be nice too. I've heard .040 clearance and 6cc worth of relief.

    Also, could anyone verify these head gasket figures. Basic Fel-Pro gasket rebuild kit being used. .041 compressed thickness with a gasket bore of 4.166.

    I'm getting a million figures from manufactures. I used the above componets with vortec heads. The heads and block have NOT been shaved. I've gotten anywhere from 9:2-10.6:1 for estimates. I figure I'll break out the paper and pencil and use math to settle this /forums/images/icons/smirk.gif .

    Thanks
     
  2. m j

    m j 1/2 ton status

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    measure it
     
  3. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Its assembled. Just curious is all.
     
  4. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    There are many variables that need to be calculated for the equation. You need to know cylinder head combustion chamber cc's, compressed head gasket cc's, piston valve relief cc's or piston dome cc's, block deck clearance cc's, and also cylinder swept volume cc's. Then you can accurately calculate compression ratio.
     
  5. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    I've got all those up in the post. Just need verification on the deck clearance and valve relief. They are vortec heads, so combustion chamer is 64cc. With .040 clearance, I'm getting 9.2:1.
     
  6. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Deck clearance can only be found by installing your pistons and measuring it. Each block can and will have a different deck clearance because GM was not that carefull about quality control. I have had a block that was off by .035" from one side to the other and also off by .012" from end to end.
     

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