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Thread: My Kilo Motor

  1. #181
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    mmm and i just ran my 49er at 100mph testing at about 2400 feet above sea level,,,honest,,,just a teaser guys,,,, but did hit 100mph,,,,, keep digging,,

  2. #182
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    Quote Originally Posted by JohnsonM50 View Post
    With the specs you gave, 1st post I find potential speed to be 70.79mph. Im not trying to cast doubt tho just to say there are variables on the boat beyond arithmetic while #s are cut & dry. The 1.85 :1 ratio with the 12 x 23 prop @ 6500Rs could potentially go 76.4. I dont know much about the powerhead except to say it will need to produce power at much more rpm. for that 83mph+ mark. At 2:1, 23P youll need a minimum of 7700 Rs to reach 83.8 & thats before subtracting slip/resistance that can vari from about 90% [very efficient] or less.
    What I do to get these #s is Pitch times RPM divided by 12, times 60 divided by 5280, times Ratio. [.5 in this case]= Potential Speed. To get ratio I divide the low # of gear teeth by the high #. for instance Yamato 14/15s = .933:1 using .933 to multiply. Best of Luck with that run for the record.
    Hi Rob I dont know where you have seen 75mph maybe behind your car! I built the boat and my mechanic Alan Downes built that motor it was the fastest 850 cc mono in Queensland Australia, I have been racing for a long time and have a lot of experience with 5 championship wins as you know, the best speed I ever saw was 71mph but in race trim 69 / 70mph when the motor was fresh and the boat was new and the bottom had just been straightened . To gain 4 mph with the same motor is a big ask. Also the 1250 record of Steve Medaris's that you want to beat was with a standard sst60 and any motor used to attempt to beat the record must be standard production and under 1250cc read your rule book for the class rules. People in Brisbane here are laughing.

  3. #183
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    Hi Derek, I can confirm 110% the boat has done 75mph with that motor on it. This thread is over 2 years old. i dont see why people are laughing? im only stating what it has done.

    I later did 78mph when i first put the mod 50 on the boat.

  4. #184
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    Quote Originally Posted by 850cc racer View Post
    Hi Derek, I can confirm 110% the boat has done 75mph with that motor on it. This thread is over 2 years old. i dont see why people are laughing? im only stating what it has done.

    I later did 78mph when i first put the mod 50 on the boat.
    Hi 850 racer. The 1250 cc mono record was set by me with a speed of 81.33mph with a stock SST 60 OMC swinging a very thin 25inch prop with the motor height right on the temperature limit and cooled down at the end of each run. The boat is identical to yours. I beleive that this speed can be bettered as I had a one way speed of arround 85 mph. In 1980 the 1000 cc mono record was set by me with a FT 19s on the original wooden version at a speed of 82.33
    mph.The FT19s was latter banned from competition as it was considered to not be a stock outboard. New records were called for and set with stock engines. I changed to a 75 hp Hustler and in 1988 set the1250 cc mono record at 76.88 mph with a 25 inch prop with the motor height on the temperatur limit and then overheated at the finish of the record attempt. As your motor is modified the speeds you state are obtainable but is all dependant on the diameter of your prop as those tha I ran were extremly thinned and less than 12 inch diameter. My kilo speeds were around 4 to 5 mph better than my circuit speeds due to a different setup and being able to swing the 25 inch prop. From memorary I think that the best revs by the stock 75 Hustler was 6400 - 6500. Are you still 850 cc racing.
    Regards
    Stephen Medaris

  5. #185
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    the straight in Mod 50 made more power than the ft19s, it is a better moda

    Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052

  6. #186
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    Fast Fred. Yes these would be faster than the FT19S but would not have been allowed in Australia as the class in which the FT19S raced were stock motor class. The SST 60 that I raced was slightly slower than the FT19S. With a finger ported 920 OMC with a 31M straight front and dual carbs the mono was achieving speeds in the low 90mph which was a lot of fun. This modified 920cc motor was unreliable and prone to seizing No 1 piston due to airpockets around that cylinder. A teltail out of the thermostat resolved this. Also the heads were prone to cracking if shaved too much.
    Regards
    Stephen

  7. #187
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    this 920 engine is this the oval port engine ? the one made between 93 and 2004 ?
    or an older engine ?

    .

  8. #188
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    bridge port makes a bigger overall Exhaust port, oval port is for a round power band and can not meet the over all size of a bridge port exhaust window. i have made good power with oval, but never as much as a bridge. i some have heard that some are makin more power with oval, reminds me of some racers that would cover there prop at the races like it was all that, thay were vary fast, too fast, for the rules . it was never the prop, it was the three trick ilegal sleves that thay had put in, cuzz of there big time last name they never got called on it, thats racin,

    Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052

  9. #189
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    bridge port have larger area than oval ?????????

    omc claimed the oval port had more exhaust area than the bridged port version from new on the standard motors that anyone could just walk in and buy.
    im not talking about specials or sst60 race engines.
    have you ever worked out the area of an oval port 56cu in engine fred, ? I have not, I am only going by what OMC claimed when the oval port 56 ci came onto the market.
    I think there might even be something about it in their sales brochure for 1995/6 ?
    being oval makes it a touch harder to actually measure the area I suppose. I have never tried, but would be interesting to actually find out.

    .

  10. #190
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    a piece of graph paper is a quick and dirty measure

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