Cam duration
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Cam duration

  1. #1
    Member $BLOWNNYS's Avatar
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    Default Cam duration

    I have purchased a used boat and believe someone built the engine with to much cam. I believe the engine is sucking in water at an idle causing small mis fires when the engine speed is below 800rpm. The engine has the stock merc exhaust, and based on seat of pant I feel the engine power band is 3000rpm and over. What maximum duration should be installed on a stock system, I have heard a 257 advertised is about the max. Have no idea whats in the engine at this time but plan on a disassemble this winter to find out.

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  3. #2
    Senior Member Boat 405's Avatar
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    Default

    With the stock exhaust I wouldn’t go over 250 duration. With good cmi headers water jacketed tail pipes you could get away with 260-270. But that’s not all of the equation. Lobe sep needs to be around 112-114. Down in the 106-110 you’ll have reversion problems.
    Boat 405.

  4. #3
    Member $BLOWNNYS's Avatar
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    The durations you are listing, are they advertised or at .050 lift? I have been checking out the marine comp cams but all have a 110 -112 lobe separation. Whats your thoughts on hyd cams verses hyd roller cams. Dont really want to set lash every year like I do on my mechanical roller in my other boat.
    hyd roller. E

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  6. #4
    Senior Member ol guy's Avatar
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    Default

    Quote Originally Posted by Boat 405 View Post
    With the stock exhaust I wouldn’t go over 250 duration. With good cmi headers water jacketed tail pipes you could get away with 260-270. But that’s not all of the equation. Lobe sep needs to be around 112-114. Down in the 106-110 you’ll have reversion problems.
    Agreed! it is more the lobe separation than duration.

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