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 rpm and prop ? 
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MMT Pro Member

Joined: Thu Dec 01, 2011 8:14 pm
Posts: 54
Post rpm and prop ?
Just a general question for the experts. Quick summary goes like this. I am now running a 9x8 hill prop on my 6.5hp surface drive and am very pleased with its performance. I am able to turn, with the gov tweaked that is, around 3900 rpms in the water. Everybody usually talks about pitch, but do you guys think I would be able to turn a 10x8 surface prop and will I gain anything? Any thoughts? I think I am getting close to the limits of this little motor and she does not have much more to give. :mrgreen: :mrgreen: I am about done tweaking her.


Fri Jul 06, 2012 4:51 am
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Joined: Sun Aug 28, 2011 4:27 pm
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Location: Utah
Post Re: rpm and prop ?
Thats alot of prop for a 6.5.Dont know if i would change it if your running good.What speeds are ya getting and what boat is it on?

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Fri Jul 06, 2012 7:00 am
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Post Re: rpm and prop ?
14x36 riveted jon, speeds right now are an honest 14-15mph, but she has alot of low end grunt and torque.


Fri Jul 06, 2012 9:20 am
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Location: Utah
Post Re: rpm and prop ?
I dont know as much as some of these guys.But i think thats pretty good for a 6.5hp motor if ya could find one to try and not have to buy it then id try it see what happens.Ya dont want to work that motor to hard.

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Fri Jul 06, 2012 1:55 pm
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Joined: Sat Jul 21, 2012 12:40 pm
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Post Re: rpm and prop ?
What brand of engine are you running? What gear ratio? What all have you done as far as mods? I'm building a 6.5 as well and trying to decide what prop to buy. 9x8 according to prop manufacturers is suitable for 23 to 27 hp but if you are getting good performance I may think about it. just hate to spend 160 + on a prop I hate.


Sat Jul 21, 2012 1:08 pm
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Joined: Thu Dec 01, 2011 8:14 pm
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Post Re: rpm and prop ?
Engine is a 6.5 harbor freight greyhound honda clone with header, high flow air filter, rejetted carb and gov a little tweaked. Gear ratio 1:63.1. I have a nice new 9x6 lite backwater inc prop if your interested. I will take 120.00 shipped.


Sat Jul 21, 2012 3:56 pm
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Joined: Sat Jul 21, 2012 12:40 pm
Posts: 20
Post Re: rpm and prop ?
Thanks, same engine I have. I will definately think about that prop and try to decide by monday/tuesday.


Sat Jul 21, 2012 5:07 pm
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Joined: Wed Jan 14, 2009 12:31 pm
Posts: 342
Location: Faribault, Mn
Post Re: rpm and prop ?
I would spend another $50 for a top (driver) pulley before spending $200 for a prop. Try closer to a 1.3:1 reduction. Getting that prop spinning a bit faster will accomplish about the same thing as adding pitch to a prop.

Mag10


Tue Jul 24, 2012 4:11 pm
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Joined: Sat Jul 21, 2012 12:40 pm
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Post Re: rpm and prop ?
That might work out if I already had a prop but I don't so a higher gear ratio won't do me much good.


Tue Jul 24, 2012 5:45 pm
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Location: Faribault, Mn
Post Re: rpm and prop ?
Sorry, that was directed at barrelburner


Wed Jul 25, 2012 8:15 pm
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MMT Member

Joined: Sat Jul 21, 2012 12:40 pm
Posts: 20
Post Re: rpm and prop ?
Oops, my bad


Wed Jul 25, 2012 8:19 pm
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MMT Member

Joined: Sat Jul 21, 2012 12:40 pm
Posts: 20
Post Re: rpm and prop ?
Barrelburnner, do you still have that 9 x 6 prop and if so is it stainless? I cant find any hill props that are "lite" so just wondering the difference.


Sat Aug 18, 2012 10:58 am
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Post Re: rpm and prop ?
Broke, prop is stainless back water inc. I told arlon at backwater my set up and this is what he specified for my hp and gearing. Prop is still available and is a longtail prop. Worked very well and I just dont run alot of mud but shallow water so I went with 9x8 for a little more speed. Guess he specified it as a lite 9x6 because he machined it for my set up. :mrgreen:


Sun Aug 19, 2012 5:10 am
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Joined: Sat Jul 21, 2012 12:40 pm
Posts: 20
Post Re: rpm and prop ?
Ok, that makes sense. I don't run much mud either, mostly open water, some is very shallow but I don't have that mucky mud, ours is different. Thinking about a 9 x 8 also

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Sun Aug 19, 2012 9:18 am
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