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Advertised Cam Duration Q?

This is a discussion on Advertised Cam Duration Q? within the Internal Engine forums, part of the LSx Technical Help Section category; What are Advertised Intake Duration /Advertised Exhaust Duration numbers as opposed to Intake Duration at 050 / Exhaust Duration at ...

  1. #1
    Member 89LX's Avatar
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    2000 Z28 M6

    Advertised Cam Duration Q?

    What are Advertised Intake Duration /Advertised Exhaust Duration numbers as opposed to Intake Duration at 050 / Exhaust Duration at 050? The advertized duration numbers are always larger. I understand the 0.050 sizeing
    but they never mention that figure when talking "advertized" numbers.
    2000 Z28 M6, SLP Lid, SLP Bellows, SLP UD,
    P&P Maf, TB By-Pass, PS Shorties, LS6 Intake, FAST 78mm TB, Hooker CB, Hurst Billet, Front Tower Brace, small 218/218....527/527....114 cam.
    337rwhp/348rwtq

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    Slow'er'Ass Mr. Luos's Avatar
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    Red Tint Jewelcoat
    2008 Trailblazer SS

    Intake:
    Degrees BTDC intake valve begins to open + 180 degrees of crank rotation + degrees ABDC intake valve begins to close = advertised duration.

    Example: 33 degrees BTDC + 180 degrees + 67 degrees ABDC = 280 degrees.



    Exhaust:
    Degrees BBDC exhaust valve begins to open + 180 degrees of crank rotation + degrees ATDC exhaust valve begins to close = advertised duration.

    Example: 69 degrees BBDC + 180 degrees + 39 degrees ATDC = 288 degrees.

  3. #3
    Senior Member mrr23's Avatar
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    dark bowling green
    2000 corvette

    back in the 'day', each manufacturer 'advertised' their cam specs at different points of lift. some .006" some .004". there was no common ground to compare cams from one manufacturer to another. it was harvey crane who came up with the idea of having everyone put up the specs of .050" lift.

    basically it's the amount of time (duration) the valves are open from beginning to ending of the event.

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    Mag Red
    2002 Vette

    There is a SAE standard that provides guidelines on cam measurement. The standard is for the measurement to be taken at 0.006" lift, with a what was standard 1.5 rocker ratio, this equates to 0.004" at the cam lobe. Isky and Comp do not follow the standard. These numbers are used to represent the valve seat timing. David Vizard's valve train book discusses this and is a very good read if you don't have it.

  5. #5
    Member 89LX's Avatar
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    Good Info

    Outstanding feedback from everyone...thanks.

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