opinions on proping my 78 140 Johnson

Ranger 330V

Petty Officer 1st Class
Joined
Sep 25, 2007
Messages
242
well I got her on the water yesterday...ran great! Idle has an occansional cough/sneeze which I'm fixing to work on. This is the deal. 78 140 on a 83 ranger 330V. 6" jackplate (manual) cavitation plate level with keel. 13 1/4 X 17 aluminum (seen better days) prop. 6300 rpm at WOT 43mph speedo tube not gps...just for a few secs to verify. Wanting to hit 5500 wide open like dhadley says to help with coking. I was by myself...no gear...1/2 tank of fuel...livewells dry....one battery when I did this. Great day to fish but needed to build fence and didnt' want to be inticed by the great weather..lol. I'm going to try a 13 X 19 stainless from a friend this week. I think I read 300 rpm or every degree?? Is this right?? if so seems I could go 21...but I was light loaded so do you guys think the 19 will be the way to go?? What about diameter on these motors?? will 13 be good or do you guys think a larger diameter will be in order? I know this should probably be in the prop section but its hard to get answers there and you guys know johnsons and what they will do. Man she sounds great when you get on her and with the 17 its like a dragster taking off. One thing though....I can't get hardly any trim out of her...kick her all the way down and take off and get up and you can't give her much trim or she'll blow out. I'm sure the eat up aluminum has something to do with that...I have the plate level with the bottom pad...I could get alot of trim out of my 1150...but it has a nice 14X19 stainless prop on it. Anyways..thank you guys so much for helping me get this motor going...she's a beast!!
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: opinions on proping my 78 140 Johnson

Props are measured in inches. Diameter X pitch.1 inch in pitch is good for about 150 to 200 rpm.Generally going to stainless will reduce the rpm some more but usually produce more speed. same pitch to same pitch.
the 19" ss prop could produce about 300 to 500 drop in rpm.It will also help combat ventilation.
 
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