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  1. #76
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    Every mod depends on what you want from the eng. You can't have it both ways. are you looking for the family truckster or a top end beast?
    A small case will most definitely give great low RPM response. This also depends on the port volume and timing. Port volume means a lot in velocity in to the cyl. To big of a port runner and you will lose velocity at low RPMs. But there is a trade off in top end flow. Transfer timing mans a lot as to where the power band will be best. High transfers will give good timed area but will reduce velocity. with out a pipe to draw the charge high transfers will not work to good. I see that tune pipes are not used on large out boards as the rules for racing do not allow this. Would be hard to have proper fuel delivery with out some very expensive testing to get it right. Could you imagine the power when it hits the pipe!!!

  2. #77
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    Quote Originally Posted by dwilfong View Post
    Every mod depends on what you want from the eng. You can't have it both ways. are you looking for the family truckster or a top end beast?
    A small case will most definitely give great low RPM response. This also depends on the port volume and timing. Port volume means a lot in velocity in to the cyl. To big of a port runner and you will lose velocity at low RPMs. But there is a trade off in top end flow. Transfer timing mans a lot as to where the power band will be best. High transfers will give good timed area but will reduce velocity. with out a pipe to draw the charge high transfers will not work to good. I see that tune pipes are not used on large out boards as the rules for racing do not allow this. Would be hard to have proper fuel delivery with out some very expensive testing to get it right. Could you imagine the power when it hits the pipe!!!
    sure but without 10 gears its useless

  3. #78
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    OK Guys please help me out! I have read over the years that tuned pipes on a 2 stroke produced more power buy using sound waves to ram part of the charge back thru the exhaust ports to in affect "supercharge" the cylinder--- not suck out the exhaust. Have I been misled ? Gary
    Last edited by olboatman; 06-27-2014 at 11:49 AM. Reason: old age!
    "12" Super Lite Tunnel (11') "88" 25 Yammy twin carb "BANANA SPLIT"
    "77" Hydrostream Viper "87" 140 Rude heavy modded w/15" mid, Bobs nose and lwp (in progress)
    "Too much is never enough" Keith Richards " Dreams become reality via hard work and perseverance" G.A.Carbonneau

    "This coming from an old man that strapped two bananas together, hung a motor on it and calls it a boat" XstreamVking

  4. #79
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    People are mixing up two stroke and four stroke scavenging theories. Interesting.

  5. #80
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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

  6. #81
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    tune pipes do both suck and blow.LOL
    the front side of the pipe pulls the charge out of the eng (scavenging) loading the pipe with fuel air mix and the back side reflects the pressure wave mad by the explosion of the fuel.
    Using a multi stage rear cone will give a much broader power band to the eng. as the pressure wave will bounce of the rear cone at different points at different RPMs. using different cone angles will control how the pipe reacts to load at different RPMs.
    multiple front cones will control how much the pipe loads up at different RPMs
    the front side loads the pipe and the back side slams it back in. all calculated by the speed of sound . The big bang in the cylinder.
    It is only symmetrical if you use a symmetrical pipe.
    Last edited by dwilfong; 06-27-2014 at 05:13 PM.

  7. #82
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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

  8. #83
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    can you explain more on the fuel charging in relationship to firing order. This is new ground for me the v two stroke.
    always looking to learn new things.

  9. #84
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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.

  10. #85
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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"
    "77" Hydrostream Viper "87" 140 Rude heavy modded w/15" mid, Bobs nose and lwp (in progress)
    "Too much is never enough" Keith Richards " Dreams become reality via hard work and perseverance" G.A.Carbonneau

    "This coming from an old man that strapped two bananas together, hung a motor on it and calls it a boat" XstreamVking

  11. #86
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    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?

  12. #87
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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.

  13. #88
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    I can see all the ex chest work that is talked about. So making the chest larger (removing the stuffing) will let more charge load up in the chest. Then a shorter wider angle tuner will pull more at top RPMS to load the large chest.
    So how much stuffing you remove will determine the tuner used.
    More stuffing removed less low end power.
    So removing too much stuffing on a stock timed eng with a stock tuner my not show a increase in power but less power?

  14. #89
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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

  15. #90
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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.

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