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Thread: My West Coast fishing machine

  1. #721
    If I recall correctly, aren't you running 1.6 ratio roller rockers?

    Based on my manual for marine performance engines that I used to build my 383's it appears that your cam specs are very close to maximum for a marine engine. In all 3 examples of suggested roller camshafts from near stock to very high performance the intake duration @.050 lift is 204 - 214 degrees intake duration and 214 - 220 degrees exhaust duration. Cam lift with 1.5 ratio rockers is .430 - .490 intake and .450 - 510 exhaust. The book suggests a lobe separation angle (LSA) of 113 - 116 for a smooth running idle and is less prone to suck water back up into the cylinders. It suggests 109 - 112 LSA as the ideal minimum for high performance marine.

    In conclusion when using a high performance cam it suggests:
    1. Choose a cam with 6-10 degrees more exhaust duration then intake.
    2. Install cam intake lobe centerline between 108 and 110 crankshaft degrees ATDC
    3. Choose a cam with 109 - 112 LSA
    4. Make sure you haven't set timing chain sprocket in the "advance" position as this can very easily cause water to be drawn into the cylinders.

    All in all from reading everything about cam choices and your cam specs I don't see a red flag anywhere other then the cam duration for both intake and exhaust are the same.
    Last edited by Bill V; 11-28-2017 at 04:58 PM.
    "Joint Venture" 1978 28' twin 2017 Vortec roller cam 383/6.3L 350hp engines - You name it, I've either replaced it, restored it, rebuilt it or repaired it. That's my job now that I'm retired.

  2. #722
    Senior Member
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    Sep 2013
    Location
    Victoria and courtenay, BC Canada
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    Quote Originally Posted by 18ftTrophy View Post
    After reading that article you might think about redoing your custom manifolds with a water break within the hot exhaust tube.
    I will be. Some how.

  3. #723
    Senior Member
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    Feb 2016
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    Camano Is. Wa.
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    I have an idea of how to make it. Make a ring out of pipe or flat stock, that is the same outside dimension as the inside dimension on the pipe on one side with a smaller dimension on the other side (tapered). Weld this inside the pipe.

  4. #724
    Quote Originally Posted by 18ftTrophy View Post
    I have an idea of how to make it. Make a ring out of pipe or flat stock, that is the same outside dimension as the inside dimension on the pipe on one side with a smaller dimension on the other side (tapered). Weld this inside the pipe.
    Could probably do a quick test to see if it works with a muffler pipe size adapter from your favorite local parts store-cut off some of the taper on an adapter and tack it in place.

  5. #725
    Senior Member
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    Sep 2013
    Location
    Victoria and courtenay, BC Canada
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    Click image for larger version. 

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    Bill. Yes the stock 1.6 ratio rockers are what I'm running. I'll have to do some investigating.

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