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Thread: Anyone ever dynoed a 20H conversion?

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    Default Anyone ever dynoed a 20H conversion?

    I was wandering about the 20H popper, conversion, toilet, whatever one wants to call it, if one was ever dynoed......If so, what horsepower did this engine actually make? I know for sure that a true stock 20H made about 23-HP off the cuff...

    I am thinking about building a 20H popper later on for A-Mod class....THANKS!!

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    Team Member JohnsonM50's Avatar
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    That is a good question, somebody's got to know.

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    I figure it may be maybe 26-27hp? The reason I think this is that the 15ss Hot Rod is reportedly about 25hp at 8500+RPM.

    The 20H popper is only no more than equal to a 15cid Hot Rod performance in 250cc Modified where the HR is allowed pipes. The "A" Mod runabouts are only one or two mph faster than the "B" stock 15ss HR runabouts and slightly less on the kilo record! I figure that pipes on the "A" Mod is at most about 1-2 more hp than stock is @ 25hp. So the 20H popper is maybe 27 at best. The 20H conversion wont beat a 20cid HR with pipes without extensive mods to the power head and running 20lbs lighter, so the "B" deflector merc is at to much disadvantage for B mod. But since I actually have 20cid merc powerhead parts I figure "why not" for an "A" mod? I could probably come across a conversion tower and header as cheap as buying a new 15HR cylinder block, pistons, rings, and pins to swap on my 20HR... and just having another engine would a lot more convenient.

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    Here's my recollection from a fading memory. KG4H 16hp, Quincy dyno. KG7H 18 hp Hubbell dyno. 20H 20 hp reference unknown. Converted 20H 24 hp , reference lost in the sands of time.

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    Team Member smittythewelder's Avatar
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    I heard 29hp at 7200, but forget the source.

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    Default Hp

    Quote Originally Posted by smittythewelder View Post
    I heard 29hp at 7200, but forget the source.
    That's a good bit! But the 20H popper runs AMH at only 365lbs, and its still not quite as fast any faster than a 20SSH that runs 400lbs minimum. The 20SS are no more than 30 hp with a blunt gearfoot with greater drag too.

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    Team Member Danny Pigott's Avatar
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    Quote Originally Posted by champ20B View Post
    That's a good bit! But the 20H popper runs AMH at only 365lbs, and its still not quite as fast any faster than a 20SSH that runs 400lbs minimum. The 20SS are no more than 30 hp with a blunt gearfoot with greater drag too.
    Remember the Yamato is a 20 cu. looper the 20 H is not, it is 1950's design . The other thing is no (offence) but the 20H's running to day or not as good as in there hay day.

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    Default HP quote

    Quote Originally Posted by Danny Pigott View Post
    Remember the Yamato is a 20 cu. looper the 20 H is not, it is 1950's design . The other thing is no (offence) but the 20H's running to day or not as good as in there hay day.
    Well, its just all in fun and interest....but Rumley says 24HP and I estimate 26-27HP. Yet, 29HP might be a stretch based on the stats I mentioned since it is still raced. I guess we can say that the Mark 20H Conversion is 24-27 horsepower respectively. There are still some good engine builders out there though that are still messing with these motors, and the other kinds are old engines just the same. One can still build a fresh 20H or any thing else as good as ever if desired I think. If anything isn't as good, maybe its just the fuel. But that would effect anybody with any engine regardless. Anyway, I wish that there was an actual manufacturers rating for this engine just for history sake. I always wondered for years what it really made, being that it was such a favorite in racing history. Ill bet a lot of enthusiasts have.

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    Team Member JohnsonM50's Avatar
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    It seemed in the time that Mercury had an odd rating system. Of course HP is just a # & only one of the factors in what makes speed. In fun & interest, somewhere in the AOMCI links I read a converted 20H produced 45hp, hard to believe of course. I also heard of a mod that should do 72mph ??, doubtful. There are some racing locally that do ok considering the A-mod competition [converts]. All in all, from an AOMCI point of view the most over rated motor going & one of the most collected & over priced.

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    Team Member zul8tr's Avatar
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    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?
    " Three may keep a secret if two of them are dead" Ben Franklin
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