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Thread: Anyone ever dynoed a 20H conversion?

  1. #11
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    Default figures

    Quote Originally Posted by zul8tr View Post
    Since popper Hp officially unknown look at it this way as an estimate. Power is proportional to V^3. From what I recall when racing in the 70's my unconverted 20H in BSH would run about 61 mph, a 20H popper about 66 set up for circuit on a hydro. Running the numbers and assuming 20 Hp for the 20H gives 20 Hp x (66/61)^3 = 25.3 Hp for the popper all else on the hydro being constant including rpm except speed. You can play with other numbers and get maybe 26-27 hp because some of the real good poppers set up right would tic at 67 mph and that gives 26.5 Hp.

    All this assumes 20 Hp for the 20H standard so the real answer is?
    The Mark 25 fishing motor was 20 actual HP. But the 20H was dynode at 23 by Hubbel I think. Doing this formula, that means that the 20H converted makes 29.13 HP.

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    I heard that the 25SS was a 25 hp engine. The 25SS and converted 20H were interchangeable to me. Same boat, same prop, same setup, same speed 64mph . Your 25 hp figure makes sense.

    Your calculation doesn't explain the KG4H. In ASH I read between 61 and 61 on the same Keller. This 16 hp motor was an anomaly that shouldn't have been able to run that fast.

  3. #13
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    Quote Originally Posted by rumleyfips View Post
    I heard that the 25SS was a 25 hp engine. The 25SS and converted 20H were interchangeable to me. Same boat, same prop, same setup, same speed 64mph . Your 25 hp figure makes sense.

    Your calculation doesn't explain the KG4H. In ASH I read between 61 and 61 on the same Keller. This 16 hp motor was an anomaly that shouldn't have been able to run that fast.
    The world is full of anomalies isn't that interesting! The relation (really a proportionality) is just that and estimate so don't expect a fit for everything. BTW what is the Hp of a stock KG4 at the reduced RPM that it was rated at compared to the 'H' engine at 7000 rpm or so on a race boat? Remember all the calc is doing is comparing the relative change in Hp for a relative change in speed (as stated rpm is not in the comparison and everything else is unchanged except speeds).
    " Three may keep a secret if two of them are dead" Ben Franklin
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    Quote Originally Posted by champ20B View Post
    The Mark 25 fishing motor was 20 actual HP. But the 20H was dynode at 23 by Hubbel I think. Doing this formula, that means that the 20H converted makes 29.13 HP.
    "I think are" the operative words, so base 20H Hp still unknown. I doubt the 29 Hp unless a popper was modded someway. BTW are all these dyno tests mentioned done at the prop shaft, or at the crank w/o the tower or with the tower and no gear foot
    " 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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    Frank Volker posted pictures of the Quincy dyno ( looks to be powerhead only ) in a thread called " Quincy Dyno and Pipe Stuff" here. I don't know what Hubbel had.

    The KG4 ( and ,I think, KG4H ) faceplate read 7 1/2 hp. Understating the hp rating helped sell motors on lakes with horsepower restrictions.

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    Quote Originally Posted by zul8tr View Post
    "I think are" the operative words, so base 20H Hp still unknown. I doubt the 29 Hp unless a popper was modded someway. BTW are all these dyno tests mentioned done at the prop shaft, or at the crank w/o the tower or with the tower and no gear foot
    I took a look at an old archive from boatsport about the services offered by Randolph Hubbel. According to the Hubbel service add, in the earlier times (1950s) they claimed that an "up front" stock "A" motor should do 15hp, and a "B" should do 21hp, a "C" do 30hp, and a "D" at 40hp all around 6000rpm.

    Now, in a 1961 add they changed the needed output for the "B" stock front runner up to 23HP with all others still the same. I assume that this was going from a KG7H to a 20H in true stock form. They did not mention or acknowledge the conversion kits as far as I could see. It was just either stock tuning or their pipes and mods alone.

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    Speed and Spray #8, June 1953, page 37. Hubbel dynoed a stock KG7 stock at 18 hp. The curves for 3 different modifications are also shown.

    It says he dynoed the powerhead so he must have used a powerhead dyno too.
    Last edited by rumleyfips; 10-25-2014 at 12:24 PM. Reason: spelling

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    Quote Originally Posted by rumleyfips View Post
    Speed and Spray #8, June 1953, page 37. Hubbel dynoed a stock KG7 stock at 18 hp. The curves for 3 different modifications are also shown.

    It says he dynoed the powerhead so he must have used a powerhead dyno too.
    As we all know the Hp at the crank is much higher than at the prop shaft. This was the reason Mr. K and C. Strang developed the tuned pipe popper tower to beat the Champion which had less Hp at the crank than the Merc 20H. Apparently the tower on the Champ didn't loose as much Hp as the 20H tower so the popper was born to beat the Champ. They never did figure out what advantage was in the Champ tower.

    Hp/torque at the prop is what the water reacts to.
    " 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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    Default 20H power

    If some one could ask John Timmons to inquire of Charlie Strang (sp) we might get a factory tested HP rating for the 20H conversion.

    In my 20H Book I have a letter from Strang while he worked at OMC written in 1992. He does not quote a horse power number but he does state the original number for the 20H was measured at the crankshaft with no exhaust cover in place and that the 20H powerhead did have more power then the Hot Rod but at the propshaft the Hot Rod with both mid sections installed had more power then the 20H. This is what he said about the power after the initial fabricated steel design was installed. Quote "The welded steel prototype pulled plenty of power on the dyno, well above the Hot Rod."

    In this letter he also stated that Edgar Rose was given the job to develop the conversion so no doubt he would also know what the power numbers were.

    David
    Old Race Boats Still Flip You Out

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    Quote Originally Posted by zul8tr View Post
    As we all know the Hp at the crank is much higher than at the prop shaft. This was the reason Mr. K and C. Strang developed the tuned pipe popper tower to beat the Champion which had less Hp at the crank than the Merc 20H. Apparently the tower on the Champ didn't loose as much Hp as the 20H tower so the popper was born to beat the Champ. They never did figure out what advantage was in the Champ tower.

    Hp/torque at the prop is what the water reacts to.
    I know that that is how the story goes. But Ive got to say, though I truly like Mercs and am working on building one, I do believe that a 20H may have had better low/mid torque on the dyno. But there is no way on earth I can believe it was more powerful than any good running Hotrod. And that's either one at the crank overall. My old "B-U" 6NHR is much faster with the open straight exaust, and that would take away any tuning if it really had it to start with. We have to remember that C.K got pi$$ed and called the final shot on that, and we know what that means.

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