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  1. #76
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    Yes 2 stroke exhaust is all about stuffing it back in as the port timing is symmetrical hence you dont have the control you need, so mix lost out the exhaust at non optimal rpms.
    Dfi fixed the fuel part but not the air part

  2. #77
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    Don't confuse single cylinder port timing with expansion chamber design - two different animals.
    On V outboards, the firing order helps with the fuel charge was the point.

    pointer

  3. #78
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    With 120 degree timing between cylinders in the same manifold and megaphone the reverse pulse from one cylinder charges the next one.
    3 and v6 engines use this effect.

  4. #79
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    Quote Originally Posted by powerabout View Post
    With 120 degree timing between cylinders in the same manifold and megaphone the reverse pulse from one cylinder charges the next one.
    3 and v6 engines use this effect.
    Do v4s do the same but at 180 degrees? Gary
    "12" Super Lite Tunnel (11') "88" 25 Yammy twin carb "BANANA SPLIT"
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  5. #80
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    Quote Originally Posted by dwilfong View Post
    So the charge that is pulled into the ex chest by the tuner is then pushed back in by the next ex pulse from the next cyl firing?
    thats the theory, change the design of an outboard megaphone and you will see a change, so it all works.

  6. #81
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    [QUOTEis a omc patent on this exolboatman;2653590]Do v4s dits the same but at 180 degrees? Gary[/QUOTE]
    They dump to common megaphone so its 90 degree pulses.
    There is an omc patent explaining it from the 60's on the web somwhere

  7. #82
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    Quote Originally Posted by olboatman View Post
    Do v4s do the same but at 180 degrees? Gary
    No, by 180° one port is full open and the other full closed; the bang from other cylinder has no effect. All you can do with 180° is have the paired cylinders share a pipe.

    At 120° with triples and multiples, 2 cylinders are always open.

  8. #83
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    Quote Originally Posted by powerabout View Post
    [QUOTEis a omc patent on this exolboatman;2653590]Do v4s dits the same but at 180 degrees? Gary
    They dump to common megaphone so its 90 degree pulses.
    There is an omc patent explaining it from the 60's on the web somwhere
    You are going to have to explain all this to me ... I have no idea where 90° pulses will come from with cylinders firing 180 apart.

  9. #84
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    [QUOTEis onlyMark75H;2653653]You are going to have to explain all this to me ... I have no idea where 90° pulses will come from with cylinders firing 180 apart.[/QUOTE]
    4 x 90 = 360
    There is only one passage in the megaphone on v4 and 2 on a v6

  10. #85
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    Then it has nothing to do with 180° degrees other than co-incidence

    You still need to explain some benefit. At 90° I think the transfer ports are generally still open and this would be a problem rather than benefit. Add to that, the fact that its about 30° before the exhaust port closes, a lot of time prior to the critical event.

    Try to dig up that patent you referenced

  11. #86
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    Quote Originally Posted by Mark75H View Post
    Then it has nothing to do with 180° degrees other than co-incidence

    You still need to explain some benefit. At 90° I think the transfer ports are generally still open and this would be a problem rather than benefit. Add to that, the fact that its about 30° before the exhaust port closes, a lot of time prior to the critical event.

    Try to dig up that patent you referenced
    What can I say thats how all OMC v4's are made. They could have very easily had it as 2 separate 2 cylinder engines but they clearly wanted all 4 cylinders to dump to one megaphone.
    I was just stating the obvious that it fires each 90 hence the pulse comes back at each 90 degrees.

    I'll find the patent.
    Last edited by powerabout; 06-28-2014 at 02:00 PM.

  12. #87
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    http://www.google.ca/patents/US3692006
    I did think there was one from the 60's?
    drawings are of the race motor but basically morphed into the 135 style.

    Just thinking, is the exhaust design to suit the dump or the pulse coming back?

  13. #88
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    3520270 TUNED EXHAUST GAS SYSTEM FOR OUTBOARD MOTOR July 1970 Miller
    3507301 COLLECTOR AND METHOD OF MAKING THE SAME April 1970 Larson
    3470690 EXHAUST HEADER October 1969 Thompson
    3385052 Exhaust system May 1968 Holterman et al.
    3233598 Marine engine February 1966 Van Ranst
    3045423 Muffled exhaust release for an outboard motor July 1962 Hulsebus
    2921567 Slot-controlled two-stroke cycle internal combustion engine January 1960 Medenus
    2858667 Water cooled exhaust manifold November 1958 Reske

    there we go, keep us all busy for hours...
    Now I just need to the find the Rick McChesney one on the etec crossflow
    Last edited by powerabout; 06-28-2014 at 02:27 PM.

  14. #89
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    How does compression and flow rate differ from a 5 peddle intake to a larger 7 peddle system? Wouldnt the flow speed be slower going in?

  15. #90
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    Quote Originally Posted by powerabout View Post
    http://www.google.ca/patents/US3692006
    I did think there was one from the 60's?
    drawings are of the race motor but basically morphed into the 135 style.

    Just thinking, is the exhaust design to suit the dump or the pulse coming back?
    I'm lost already doesn't the first line say 3 cylinders or multiples?

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