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Thread: What makes Compression

  1. #1
    Join Date
    Jul 2001
    Location
    Chicago, IL
    Posts
    253

    Default What makes Compression

    When looking at the JH engine specs versus the Golf engines, same cylinder size, piston rod and stroke - is it the shape of the piston that gives the 10:1 versus 8.5:1 compression? aren't the cylinder heads essentially the same (except for solid versus hydraulic lifters)? thanks

  2. #2
    Join Date
    Jan 2001
    Location
    Flagtown, NJ USA
    Posts
    6,334

    Default

    Compression ratio is the ratio of the total cylinder and head volume w/ the piston at the bottom of it's stroke over the remaining volume of the cylinder and head w/ the piston at the top of it's stroke.

    While I haven't had a Golf 10:1 motor apart, I do believe that the shape of the piston 'dome' is different, and subsequently decreases the amount of 'residual' volume when the piston is at the top of its stroke.

    This volume represents a much smaller portion of the total volume than it does the residual volume, that's why the CR goes up.

    ------------------
    MARRS #25 ITB Rabbit GTI

  3. #3
    Join Date
    Oct 2001
    Location
    Issaquah ,Washington
    Posts
    9

    Default

    Bill is correct, the pistons are different. They have a smaller volume dome.

    Peter

  4. #4

    Default

    Hmmmmm...so if I slap on a set of these 10:1 pistons on my Rabbit motor...........
    ------------------
    Glenn
    MARRS ITB #07
    dead...for now

    [This message has been edited by GTI Cup (edited October 12, 2001).]

  5. #5
    Join Date
    Jan 2001
    Location
    Flagtown, NJ USA
    Posts
    6,334

    Default

    It will be illegal in ITB!!!


    But it will be legal in GProd!!!!

    ------------------
    MARRS #25 ITB Rabbit GTI

    [This message has been edited by Bill Miller (edited October 12, 2001).]

  6. #6
    Join Date
    Oct 2001
    Location
    Issaquah ,Washington
    Posts
    9

    Default

    Forget golf pistons, how bout Audi pistons. I can't remember what model, but you will end up with 10:1 cr and a total displacement of 1870cc. All totally illegal of course.

    Peter

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