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Thread: Fast Fred's Secrets of the OMC MOD50's Thread #1

  1. #81
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    Default Porting ?

    What kind of porting did you do to make this type of Exhaust work ?

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    on page one of the tred

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    Team JDS Jeff Akers's Avatar
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    Quote Originally Posted by Fast Fred
    kinda like this but w/ a slippy can on it

    YOU BUILD IT I"LL BUY IT
    Jeff 93-C



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    Default Exhaust

    Fred,
    Thats a great looking exhaust but not what you want for the Mod 50. Port runners are going to be way too long. If you think about the systems used on the Mod 50 & Merc V6 they are very simular. Merc V6 is tuned as if it were two 3-cylinder engines. I doubt you will have any luck finding the original pattern equipment for the FR-19, I am sure it was scrapped years ago. The system used on the -31 is excellent, except it goes on the wrong side of the engine. Here is something to think about -- what happens if you put the outlet at the top of the block? Don't laugh.

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    Sam Cullis Mark75H's Avatar
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    Quote Originally Posted by NERSTROM
    Here is something to think about -- what happens if you put the outlet at the top of the block? Don't laugh.
    Wouldn't that sort of be like changing the firing order or running the motor backwards .... or ... turning the motor inside out and putting the exhaust on the other side of the block?
    Since 1925, about 150 different racing outboards have been made.


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    no, the firing order is the same on the m-31, spins the same direction as the 19s, the m-31 had a better intake flow , it was also said that the rings sealed
    better on the exhaust side of the piston in the m-31.

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    my self, i got to dump in to the midsection, thats the rule.
    i'm running an FT-19s ( nitro L/U with trick bigfoot nose cone, SHIFTABLE. thats
    another rule on a vary short list). the hull has a 13" tunnel, it has to carry it self at all times, torque, got to have a bunch of low end

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    Sam Cullis Mark75H's Avatar
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    With the same crankshaft, the actual firing order is the same .... but the motor with the exhaust on the other side is in essence reversed on the crankshaft .... for the exhaust tuning the firing order is reversed. Jim asked what the effect would be of letting the exhaust out the top of a regular motor .... it would be the same effect .... changing the exhaust tuning's firing order
    Since 1925, about 150 different racing outboards have been made.


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    interesting, please explain how changen the order of the lengths dose something.
    thinkin it needs a reflective cone, the closer the better, like a bumble Bee, in line, on the top.

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    Quote Originally Posted by Mark75H
    Jim asked what the effect would be of letting the exhaust out the top of a regular motor .... it would be the same effect .... changing the exhaust tuning's firing order
    Sam; I believe you are over-thinking this situation. All three cylinders are [must !] exhausting into the same chamber, each one firing at 120 deg intervals. The pressure pulse felt by the next firing cylinder [120 deg later] is the same whether one exhausts top or bottom. I have made up two MOD50 clones from billet exhausting out the top, with good results.
    Cheney Street also went out the top, and his 105 run still stands !
    Biggest problem is folks throwing their gum wrappers in there, others calling it the 'slurppy exhaust', cause the tapered cone sitting on top lookes like one. But it is great fun to leave a oily rag in the pipe, and have it exit flaming on fire up!

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