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Thread: Unicorn :Compresion ratio [Update 1]

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    Rusted viv.nomad's Avatar
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    Default Unicorn :Compresion ratio [Update 1]

    finally i have decided to try to increase compression ratio on my v1 uni and by the calculation and assumin the metal i m going to remove will result in volume change which would be equal to volume of cyllindrical shape of radius [bore\2] and length that i removed \ shaved from block .

    for 9.6 : 1 compression ratio the length i should remove came out to be .4 mm

    it is like

    SV = pi*(57.3\2)^2*57.8*(1/1000) = 149.05 cc

    default CR 9.1:1

    so CV = SV \ (9.1 - 1) = 18.4 cc

    now if i remove 0.4 mm from the block

    volume change = pi*(57.3\2)^2*0.4 *(1/1000) = 1.03 cc

    new CV = 18.4 - 1.03 cc = 17.37

    hence new CR
    (149.05/17.37)+1 = 9.58 : 1

    should i go ahead any other adjustment required?????

    and how much can i increase CR without worrying abt any thing!! max value??????

    UPDATE 1:
    Compression ratio mod is complete , sattled for 10.1:1

    http://www.xbhp.com/talkies/help-me/...tml#post223651
    Last edited by viv.nomad; 06-09-2009 at 02:19 AM.

  2. #2
    MG
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    Query Approved

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    Quote Originally Posted by viv.nomad View Post
    how much can i increase CR without worrying abt any thing!! max value??????
    Just make sure that the engine is not knocking and valves do not bang into the piston. You can increase the CR to that limit.
    Your biking tells a lot about the person you are!

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    u sure??

    share some exp!!

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    I do not have any practical experience dude. But, AFAIK these are the two factors that limit the compression ratio. Maybe others with practical experiences can confirm.

    And your calculations are correct!
    Your biking tells a lot about the person you are!

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    that are max physical borders.. i was talking abt limit where only increasing CR will give performance and it may not involve other component adjustment like valves..

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    Quote Originally Posted by viv.nomad View Post
    that are max physical borders.. i was talking abt limit where only increasing CR will give performance and it may not involve other component adjustment like valves..
    Increasing your CR up to these physical limits will improve performance irrespective of any changes in the valve timings. However, after a certain point, ignition timings will need to be changed to allow further increase of CR till the limits.
    Your biking tells a lot about the person you are!

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    woich to .. are bhai kab ignition timing change karne ki jururat padti hai.... kis CR k baad..

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    Quote Originally Posted by viv.nomad View Post
    woich to .. are bhai kab ignition timing change karne ki jururat padti hai....
    That depends on how the bike is currently set up. I do not have any idea about the unicorn. If ignition timings are not retarded, knocking may occur.

    You can do one thing - go ahead and shave the 0.4mm from the head. If knocking occurs you will have two choices - use double head gasket to decrease the CR a bit, or use high octane petrol.

    If everything is fine, go ahead and shave a bit more. If knocking occurs again use double head gasket or high octane fuel.

    So, the idea is to discover the limit of your bike with the current timings.
    Your biking tells a lot about the person you are!

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    you'll come to know when your engine knocks

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