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Thread: 4agze compression ratio

  1. #1
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    Default 4agze compression ratio


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    Hey guys what would a trd 0.5mm head gasket bring 4agze 8.0:1 compression ratio to ? been trying to find the conversion formula , unable to find it. Also anyone running this headgasket with a turbo ?
    Last edited by reecegze; 18th March 2009 at 11:23 PM.

  • #2
    Veteran Jonny Rochester's Avatar
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    Let us assume, the swept volume is 1600ml.

    If all pistons were at the top, the room (C) in the chamber for gas would be:
    (1600 + C) / 8 = C
    funny maths...
    C = 228.5ml

    Let us assume the bore is 81mm, and a normal gasket is 1mm thick.
    Volume used by a normal gasket is:
    (3.14 x 81^2) / 1000 = 20.612

    Volume used with thin gakset is half that, = 10.306

    New C = 228.5 - 10.306 = 218.194

    New compression ratio =
    (218.194+ 1600) / 218.194 = 8.33 : 1


    I probably have this wrong. Failed maths...
    Last edited by Jonny Rochester; 19th March 2009 at 12:37 AM.

  • #3
    Senior Member Hen may possibly be a nut's Avatar
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    Johnny, I get slightly different numbers through the working, but exactly the same result. I think you are out by a factor of 4 in both C and gasket volume, but for different reasons.

    C (for a single combustion chamber):
    (400 + C) / C = 8 ... so C = 57.14 cc

    Area of a circle is (depending on radius or diameter measurement):
    pi * r^2
    or
    pi * D^2 / 4

    So the volume reduction for each combustion chamber, given the thinner gasket is:
    V = 0.5 * pi * 81^2 / 4
    V = 2576 mm^3
    V = 2.576 cc

    New CR = (400 + 57.14 - 2.58) / (57.14 - 2.58)
    New CR = 8.33

    Which is exactly what you got too...

    But also bear in mind that all this is based on ideal numbers, that the head has never been shaved, and the bores are standard etc, etc, etc. It gives you an idea, but I wouldn't bet on any exact figures.
    Last edited by Hen may possibly be a nut; 19th March 2009 at 02:11 AM.

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    pffft yeh jonny how could you fuck a simple thing like that up.


  • #5
    Veteran Jonny Rochester's Avatar
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    Sorry, I was working too quick for you. The 4 cancels out because I have 4 cylinders, as I was doing total volumes of the motor, not just one cylinder.

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    awesome guys. I was thinking around 8.5:1 area

    cheers

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