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rpm and prop ?
http://www.mudmotortalk.com/mmt_v2/viewtopic.php?f=41&t=30545		 Page 1 of 1
Author:  barrelburner [ Fri Jul 06, 2012 4:51 am ]
Post subject:  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.
Author:  mud slinger 69 [ Fri Jul 06, 2012 7:00 am ]
Post subject:  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?
Author:  barrelburner [ Fri Jul 06, 2012 9:20 am ]
Post subject:  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.
Author:  mud slinger 69 [ Fri Jul 06, 2012 1:55 pm ]
Post subject:  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.
Author:  Broke Okie [ Sat Jul 21, 2012 1:08 pm ]
Post subject:  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.
Author:  barrelburner [ Sat Jul 21, 2012 3:56 pm ]
Post subject:  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.
Author:  Broke Okie [ Sat Jul 21, 2012 5:07 pm ]
Post subject:  Re: rpm and prop ?
Thanks, same engine I have. I will definately think about that prop and try to decide by monday/tuesday.
Author:  Mag10 [ Tue Jul 24, 2012 4:11 pm ]
Post subject:  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
Author:  Broke Okie [ Tue Jul 24, 2012 5:45 pm ]
Post subject:  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.
Author:  Mag10 [ Wed Jul 25, 2012 8:15 pm ]
Post subject:  Re: rpm and prop ?
Sorry, that was directed at barrelburner
Author:  Broke Okie [ Wed Jul 25, 2012 8:19 pm ]
Post subject:  Re: rpm and prop ?
Oops, my bad
Author:  Broke Okie [ Sat Aug 18, 2012 10:58 am ]
Post subject:  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.
Author:  barrelburner [ Sun Aug 19, 2012 5:10 am ]
Post subject:  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:
Author:  Broke Okie [ Sun Aug 19, 2012 9:18 am ]
Post subject:  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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