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Discussion Starter · #1 ·
hi

im wondering if someone could tell me what the best size and pitch would be or how to calculate it out? My boats a 17' flatbottom with a ford FE around 400hp and 9* gears in the v-drive.
 

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I had a 19' Schiada, ran 22 gears and 11 1/4 x 16 prop, turned 7000 + rpm. Its in the Orilla area I believe
I would be sure of the FE Hp prior to 1973 and past could be a 352- 427 CI. Thats 200 -425 HP. FE parst are hard to find and expensive.

If its 352 12 gears two blade 11 x 11 1/4 14 or 12 x 14 three blade about 4500 rpm possible 5000. Two blade will give you 5000 +

I have run 352,390,427 FE engines.
 

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Discussion Starter · #3 ·
its a 68 390 gt motor which is bored .60 with a 428 crank and 2 600 carbs. im thinking 6 grand would be the highest i would want to rev it. I was told a 11.25x15 2 blade would be a good prop on a dfferent forum. does that sound right?
 

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Yes it would,remember more pitch more speed. Gears also play a factor in thi equasion. If you can turn 15 pitch x 6000 x gears(12%) would be 6000 + 720 = 6720 x 15 =100800 divide 1056 = 95.45 mph - slippage 10% would be 85.90 mph. Remember slippage comes from all the factors above,hull, prop,diameter prop.

Useing this formula gives you an idea what you have to strive for
 

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SS 201, you're way low on the slip factor at 10%. You are correct that all boats have different slip factors. Rule of thumb on correctly setup lake boats is 10% for hydro's and 15% for flats. I confirmed this with my flat at Bakersfield with an actual timeslip. I spun 6,600 rpm w/ 25% gear and a 15 pitch prop. The timeslip was 100.50 mph.
An older style heavy flatbottom may even have closer to 18-20% slip.
Jocko
 
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