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Thread: Mercs and megaphones--thinking the unthinkable?

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    Brilliant! The length can also be adjusted with sliding sections, as kart racers do.

    On the subject of "it's already been done" and "can't make any more improvements", this is historically untrue. Some smart person out there is sure to come up with a trick no one thought about before (or didn't act on/ do it right) and another small increase is achieved.

    Look at emissions in cars as an example. When this all began--in the mid-70s--car engines were God awful! Not only did they barely run, they were powerless slugs. Bleeck! (You older guys know what I'm talking about.) But over the years the horsepower has come back--big time!--and new cars are so clean they are air cleaners in some smoggy areas: the air coming out the back is cleaner than the air coming in! Amazing. But all this improvement took time--one little thing at a time.

    Jeff
    "We live at the bottom of an ocean of air." - General Marvage Slatington

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    Quote Originally Posted by Fastjeff57 View Post
    Brilliant! The length can also be adjusted with sliding sections, as kart racers do.

    On the subject of "it's already been done" and "can't make any more improvements", this is historically untrue. Some smart person out there is sure to come up with a trick no one thought about before (or didn't act on/ do it right) and another small increase is achieved.

    Look at emissions in cars as an example. When this all began--in the mid-70s--car engines were God awful! Not only did they barely run, they were powerless slugs. Bleeck! (You older guys know what I'm talking about.) But over the years the horsepower has come back--big time!--and new cars are so clean they are air cleaners in some smoggy areas: the air coming out the back is cleaner than the air coming in! Amazing. But all this improvement took time--one little thing at a time.

    Jeff
    Look out, Charlie Strange and Mr. Christner!!! (Champ20B) just come up with a way to help make mod motors their fastest!!

  3. #43
    modifiedoutboard OUTBOARDER's Avatar
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    Default as Speed insreases resistance in creases exponentially

    Quote Originally Posted by Dixon263 View Post
    There is something that I've never been able to figure out and never heard a good explanation either. Here's the deal, I own a Stuska water brake dynamometer (130 hp max, 14,000 rpm) and have dyno'ed many four cylinder 44 cu in Mercs in quiet form. They dyno real close to 40-41 hp in stock, quiet form with a great horsepower curve. I chose to dyno directly off the driveshaft to reduce unneeded wear on the "D" Quicksilver or 45SS unit. A friend with a 12' 6" hydro saw 79 mph many times but never broke 80. We put his motor on the dyno and pulled 40.6 hp in the 6500 rpm range consistently. Then we installed a set of Parker megaphones and saw 57 hp with a wide power curve that was right in the range the motor would be run at for top end. A trip to the water saw some odd results, 79 mph and not a tiny bit faster. The pipes still made good hp to well over 7000 so we were definitely in the higher hp range. With megaphones, at top speed, the motor was developing close to 50% more hp, but was not able to go ANY faster.

    Before I present a possible theory, here is another example. I modified a '44 with single ring Turner pistons, mild porting used the larger KC carb instead of the KA's. The dyno showed 46 hp, in quiet form again. A trip to the water showed a max top speed of 85 mph, quite a difference from my usual 78-80 bests. So what is going on here? These tests are not flukes but consistently this is the way it will go every time. So here is a possible theory. After decades of racers using megaphones on Mercs, is it actually possible that somehow the high speed air that flows across the pipes is cancelling the 50% gain shown on the dyno? I realize that this a big pill to swallow, but something is really wrong with this picture. 50% more power being applied to the prop at top end and not any more speed at all? I have a friend that manufactures the 'Hurricane' 27 hp industrial leaf blower that will move a large volume on air at 160 mph, I guess it would be interesting to set it up in front of the dyno with a megaphone Merc running at 57 hp and turn the air on. Any other ideas on this one?
    as speed increases Resisteance "Drag" from air increases exponentially so does resistance to lower unit.
    Speed as a function of Horse Power thru air alone can be expressed by

    V(hp)air = K * (square root of HP)

    example 14' Gw invader goes 72 mph with 90 hp aired out.
    so K = V/sqrt hp = 7.8
    with 100 hp goes as follows
    V(hp) = 7.8 * sqrt 100 = 78mph very close to reality
    this is very simplified and will still be very close over a small range.
    (if you look at any function/formula at a small enough interval a straight line will approximate)

    with all this said the prop may not be taking advantage of hp increase at certain speeds/conditions etc............test test tes
    ANTHONY McCULLOCH
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    Team Member zul8tr's Avatar
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    Quote Originally Posted by OUTBOARDER View Post
    as speed increases Resisteance "Drag" from air increases exponentially so does resistance to lower unit.
    Speed as a function of Horse Power thru air alone can be expressed by

    V(hp)air = K * (square root of HP)

    example 14' Gw invader goes 72 mph with 90 hp aired out.
    so K = V/sqrt hp = 7.8
    with 100 hp goes as follows
    V(hp) = 7.8 * sqrt 100 = 78mph very close to reality
    this is very simplified and will still be very close over a small range.
    (if you look at any function/formula at a small enough interval a straight line will approximate)

    with all this said the prop may not be taking advantage of hp increase at certain speeds/conditions etc............test test tes
    Thru air or water per basic physics, Drag (a force) varies as the Velocity squared, Power varies as force x velocity, so Power (Hp) varies as Velocity cubed ======>> or Hp varies as V^^3

    or in your form, V = K *(cube root Hp)

    Running the numbers with a new K value your 10 hp increase (90 to 100) will not yield a 6 mph increase (all else remaining constant) but about 2.6 mph increase or 74.6 mph.

    As always testing is the last word
    " Three may keep a secret if two of them are dead" Ben Franklin
    " ------- well Doctor what have we got a Republic or Monarchy? A Republic he replies if you can keep it"
    Benjamin Franklin, 1787 Constitutional Convention, as recorded by signer James McHenry's in his diary at the Library of Congress

    Location: SW Orlando, Fl

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    To simplify this........72mph divided by the square root of 90hp equals 7.6

    now, we take 7.6 and multiply it times the square root of 100hp (since we are souping up the boat) and we then get 76mph......all answers rounded off.


    72/sqrt of 90=7.589 7.589 X [sqrt(100)]=75.89mph (75.89)-72=an increase of 3.89mph going from 90 to 100 hp

  6. #46
    Team Member zul8tr's Avatar
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    Quote Originally Posted by champ20B View Post
    To simplify this........72mph divided by the square root of 90hp equals 7.6

    now, we take 7.6 and multiply it times the square root of 100hp (since we are souping up the boat) and we then get 76mph......all answers rounded off.


    72/sqrt of 90=7.589 7.589 X [sqrt(100)]=75.89mph (75.89)-72=an increase of 3.89mph going from 90 to 100 hp
    Not quite you are not simplifying anything with the wrong relation, as I note above the relation from basic physics is a cube root function:

    V = K *(cube root Hp)

    K = 72/ (cube root 90) = 72/4.48 = 16.07

    V = 16.07 x (cube root 100) = 16.07 x 4.64 =74.6 mph a 2.6 mph increase all else being equal which generally never happens. As always testing is the final answer.
    " Three may keep a secret if two of them are dead" Ben Franklin
    " ------- well Doctor what have we got a Republic or Monarchy? A Republic he replies if you can keep it"
    Benjamin Franklin, 1787 Constitutional Convention, as recorded by signer James McHenry's in his diary at the Library of Congress

    Location: SW Orlando, Fl

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    Quote Originally Posted by zul8tr View Post
    Not quite you are not simplifying anything with the wrong relation, as I note above the relation from basic physics is a cube root function:

    V = K *(cube root Hp)

    K = 72/ (cube root 90) = 72/4.48 = 16.07

    V = 16.07 x (cube root 100) = 16.07 x 4.64 =74.6 mph a 2.6 mph increase all else being equal which generally never happens. As always testing is the final answer.
    I know.......but I was referring to the first formula mentioned.

    I agree, testing is the final truth and/or proof of it all as well. But I did think that resistance is simply the measure of force alone as to determine/estimate "energy(horsepower)". Without resistance, force couldn't be recognized in the coarse of movement.

    The function is: W=f(D)

    this is ........work= force X distance

    If you calculate work in unit weight with time it takes , then you find horsepower. There is only one force factor and if the horsepower is known as well as speed, then you get an efficiency factor as to use to estimate possible results of greater hp.

    Another way to describe horsepower is rotating force in number of rotations in given time (minutes) when referring to motors. That would be: f(d)/t..... I hope I got it right.

  8. #48
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    14' gw Invader 90 hp = 72 100 = 78. The boat is dragging less in water.
    So V(hp) = k*(hp)^.5 works on planing hulls (racing) over small intervals.
    air resistance increases proportionally to Velocity Squared. recall your basic diferential equation course word problem.

    water resitance increases proportinally to velocity cubed. used for discplacemant hulls like the USS United States.

    any way my 14' john did 25mph with 15hp and did 36mph with a 30hp. it works on planing hulls that are not draggin in the water.

    yes very simplistic indeed but useful
    ANTHONY McCULLOCH
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    Quote Originally Posted by zul8tr View Post
    Thru air or water per basic physics, Drag (a force) varies as the Velocity squared, Power varies as force x velocity, so Power (Hp) varies as Velocity cubed ======>> or Hp varies as V^^3

    or in your form, V = K *(cube root Hp)

    Running the numbers with a new K value your 10 hp increase (90 to 100) will not yield a 6 mph increase (all else remaining constant) but about 2.6 mph increase or 74.6 mph.

    As always testing is the last word
    sqrt did not mention cubed
    ANTHONY McCULLOCH
    modifiedoutboard@hotmail.com

    Some things never change!

    They Want it cheap..............

  10. #50
    Team Member zul8tr's Avatar
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    Quote Originally Posted by OUTBOARDER View Post
    14' gw Invader 90 hp = 72 100 = 78. The boat is dragging less in water.
    So V(hp) = k*(hp)^.5 works on planing hulls (racing) over small intervals.
    air resistance increases proportionally to Velocity Squared. recall your basic diferential equation course word problem.

    water resitance increases proportinally to velocity cubed. used for discplacemant hulls like the USS United States.

    any way my 14' john did 25mph with 15hp and did 36mph with a 30hp. it works on planing hulls that are not draggin in the water.

    yes very simplistic indeed but useful
    The basic physics relation (Drag proportional Velocity squared and Power proportional to Velocity cubed) I stated still applies, it's the K that is variable with different conditions of boat operation. You stated that "The boat is dragging less in water" which is contradictory to what I stated in my posts above and implied when using the formula that "all else remaining constant". "K" is NOT constant. The calculated value based on a single velocity and Hp was used for the increased Hp to estimate velocity to keep consistent with your approach. There are many variable conditions going on to apply a single K value to all operation conditions.

    Relations noted here (K usually known as Cd - coefficient of drag):

    http://en.wikipedia.org/wiki/Drag_(physics)

    Examples for drag and power (air drag used here but same applies to water drag and Cd still not constant but used that way for easy relative to compare calculations)

    http://phors.locost7.info/phors06.htm

    Let's get this post back on track regarding megaphones!
    " Three may keep a secret if two of them are dead" Ben Franklin
    " ------- well Doctor what have we got a Republic or Monarchy? A Republic he replies if you can keep it"
    Benjamin Franklin, 1787 Constitutional Convention, as recorded by signer James McHenry's in his diary at the Library of Congress

    Location: SW Orlando, Fl

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