20hp/test results after raising motor

[davejnz]

87 Johnson 20hp with a OMC 10/13 aluminum prop.I was turning 4900RPM's but after reading about x dimension in the forums here,i realised my AV plate was about an 1" lower than the bottom of my hull.I raised it up to 3/4" above the bottom and am very happy with the results.25.4mph(GPS) at 5050RPM.I was able to get to 5100 but didn't get to verify speed at that RPM.While testing,the boat was fully loaded.I still think i need to get my RPM's up so i'm probably gonna go with a 12 or an 11 pitch,hopefully a stainless steel that will bite better because my current setup seems to blowout during tight turns.

 

[fireman57]

Re: 20hp/test results after raising motor

If it is blowing out on the turns then you probably are at or almost at your max on height. Dhadley will probably see this thread and help you on the setup. He is one of the best. Not saying that other here don't know what they are talking about but after reading his threads and helping me, he is good. This will probably get moved to non repair outboard discussions.

 

[davejnz]

Re: 20hp/test results after raising motor

I forgot to mention my top speed was taken while running with the tide.When running against it,top speed was 23.4mph@5050RPM.I'm off to the Intercoastal tonight to do some testing with just me(light load) to see what i can get.

 

[Dhadley]

Re: 20hp/test results after raising motor

I agree about the better prop. SS is the way to go. While youre testing with the aluminum prop dont worry too much about the venting. Its expected and we're only after how the motor and hull react to X dimension changes. So far it looks like your combo responded very favorably.<br /><br />Dave, I have some Turbo props that we've tested. If that is of any interest to you just e-mail. Just to be sure, count the splines. Unfortunately I will be on the road all week (Mon - Fri) so I will have limited computer access. But I'll get back to you as soon as I can.

 

[davejnz]

Re: 20hp/test results after raising motor

Turbo was the prop i wanted to get anyway so that <br />would be great.I'll drop you an e-mail this wk on it.I got to do some more testing this evening with just me.Results were pretty much the same although top speed running against the current was a little better(24.3mph/5100rpm)

 

[G DANE]

Re: 20hp/test results after raising motor

You could look at E-bay for a 25 or 35 HP carb between 80-88 now and then. Your 20 HP has a nylon limiter in the carb throat, reducing it from 25 HP. Cylinder head is different too, but if you change carb, you cant tell difference from a 25. Continue the prop work, too, it pays off.

 

[davejnz]

Re: 20hp/test results after raising motor

thanks for the advice,I'll keep an eye out for one.I had considered trading up for a 25 or 30 but this motor has never let me down/stranded over the past 3yrs that i've had it.Here in FL,it gets used all yr and i'm on the water twice a week.