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Thread: Racing exhaust for laker 49 OMC

  1. #81
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    Hi Tim
    Yes so the V6 could whilst keeping the banks separate?

  2. #82
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    Default Banks of three

    Quote Originally Posted by Powerabout View Post
    Hi Tim
    Yes so the V6 could whilst keeping the banks separate?
    Yes, any engine with banks of three: Exhaust systems should be separated.

    In it's truest form, each bank of three should have exhaust ports located on the piston thrust side (starboard side for a RH engines as viewed from the top like the Mod50). V6's power is compromised because the banks feed a central exhaust cavity (the tower).

    Does anyone care to guess why?

    Tim

  3. #83
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    you gave away the answer ( almost)

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    Default Get 'em thinking

    A strong hint......... Looking for the technical reason for the phenomenon. Willl give a few days.

    Tim

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    Narrowness. If the exhausts BOTH exited to their port side, the motor would be both wider and non-symetric.

    Jeff

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    Default Restated question

    Indeed, centralized exhaust is used to keep the engine slender. But the questions is:

    Why does one bank produce less power than the other even though they both have 120 degree spaced pulse tuned exhaust?

    Try again,

    Tim

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    Okay; the crank is spinning in an opposite directions relative to the charge flow into the transfer ports.

    Jeff

  8. #88
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    corriolis effect?
    should you run the engine backwards in the southern hemiphere?
    and maybe the bores shouldnt be round?

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    Default Down under

    The Corriolis effect would only apply to engines near the equator, and we all know engines spin backwards down under - LOL - that only means the opposide bank would produce less power. But why?

    Tim

  10. #90
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    Quote Originally Posted by Tim Kurcz View Post
    Be aware the V6 is actually two banks of triples, each with 120 degree firing order spacing. The triple "pulse tuning" phenomenon only works with this configuration (or multiples thereof).

    Twins, fours, and early Merc in-line sixes tuned with 180 degree alternate firing pairs do not get the 120 degree tuning advantage. It should be noted that Mercury later rephased inline six cranks to take advantage of twin stacked triple exhaust tuning.

    The answer to your question is no. Engines with other than 120 degree firing order cannot take advantage of the the simple "open chest" exhaust design.

    Tim
    Merc used 3 + 3 exhaust tuning on the inline 6's starting with the first gearshift motors. Generally the firing order was alternating pairs for balance with odd/even exhaust coupling (1, 3 & 5 in one group and 2, 4 & 6 in the other). The disadvantage was length between these 3 cylinder exhaust groups favored power in the 5,000 rpm range rather than the 8,000 rpm range.

    Its not that it wasn't there, it just wasn't there for super top end.

    On the T-2 and T-2x race motors they welded 2 3cylinder 49ci cranks together to get 3 + 3 exhaust tuning with close spacing, 1, 2, 3 in one group and 4, 5, 6 in the other exhaust group. Again there was a problem with length ... the original T-2 set up put them TOO close for 7,000-8,000 rpm. Like these OMC side exhausts ... the T-2X used an extended exhaust chest to drop the tuning into the 7,000-8,000 rpm range and get almost 20 hp over the T-2.
    Since 1925, about 150 different racing outboards have been made.


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