Recommend gear ratio

Automotive powered airboat discussion.
Cmcintosh721
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Recommend gear ratio

Postby Cmcintosh721 » Tue Aug 05, 2014 1:47 pm

I'm building a boat an have a 3 blade water walker 80" maximum prop an have a 400 small block complete roller motor around 475hp what ratio reduction unit should I buy

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Birddog247
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Re: Recommend gear ratio

Postby Birddog247 » Tue Aug 05, 2014 2:35 pm

I would first make sure what rotation the prop is. Left or right
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Cmcintosh721
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Re: Recommend gear ratio

Postby Cmcintosh721 » Tue Aug 05, 2014 2:57 pm

Right hand rotation

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Deano
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Re: Recommend gear ratio

Postby Deano » Tue Aug 05, 2014 2:59 pm

That part is easy.
If it is a Maximus, it is right handed. The left hand counterpart is the Sirius.

Gearing would depend on RPMs you are going to turn your engine.
If you're turning it about 5200 then a 2.3x gear would work.
If you're turning it about 5500 then a 2.5 gear would work.
If you're turning it more like 5900 then a 2.6x gear would be what you want.

Those blades should turn 2200 max at wide open throttle, a little more pitch and a less rpm is fine.
top engine rpm / 2200 (prop rpm) = gear ratio

And congrats on your prop ! You're gonna love the push. :thumbleft:
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Cmcintosh721
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Re: Recommend gear ratio

Postby Cmcintosh721 » Tue Aug 05, 2014 3:17 pm

Thank you sir that's exactly the info I was looking for thank you

Cmcintosh721
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Re: Recommend gear ratio

Postby Cmcintosh721 » Tue Aug 05, 2014 3:25 pm

Does anybody know anything about the precision gear drives out of Oviedo fl

swamp rat70
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Re: Recommend gear ratio

Postby swamp rat70 » Tue Aug 05, 2014 4:30 pm

there decent boxs but only come in 2 to 1 ratio so would be little low at only 4400rmp on motor i had one of the first new big shaft ones he made , i was the test boat lol
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Brotherbob
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Re: Recommend gear ratio

Postby Brotherbob » Tue Aug 05, 2014 5:10 pm

For whatever it's worth I run the same prop and about the same HP ,I run a 2.88 Stinger Gear drive in a 15' Air Ranger and its a real hot rod.
It turns lots o RPM 6200 to be exact and burns fuel but she can get up and run son. It's like a really fast bulldozer!LOL!
BB
BRAB41,TAA-220 ,Air Ranger 15x8 , SBC , 78 " 3 blade WW prop, 2.88 Stinger
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Cmcintosh721
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Re: Recommend gear ratio

Postby Cmcintosh721 » Tue Aug 05, 2014 10:05 pm

That is def a lot of rpms I'm thinking about keeping mine around 5600

Sniper
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Re: Recommend gear ratio

Postby Sniper » Wed Aug 06, 2014 7:11 am

2.68 is a great ratio
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ptr34
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Re: Recommend gear ratio

Postby ptr34 » Wed Aug 06, 2014 9:55 am

I have a used 2.5 ballistic box for u. 2900
if u don't run dry .then should have gotten a bassboat
tons videos on YouTube ptr34

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skinny99
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Re: Recommend gear ratio

Postby skinny99 » Wed Aug 06, 2014 10:18 am

ptr34 wrote:I have a used 2.5 ballistic box for u. 2900


That's a deal and a good combo for your 400. Lots of torque there most likely.
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OLD MAN JONES
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Re: Recommend gear ratio

Postby OLD MAN JONES » Wed Aug 06, 2014 12:25 pm

Sounds like that 2.5 might be your Hucleberry :)

I'm betting you'll love it. Also it should keep your fuel burn down a tad and increase engine life expectancy by a fair amount.
JMHO...
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