gear ratio on 1997 johnson 150

[90srtatos]

does anyone know the gear ratio on this motor?

 

[90srtatos]

Re: gear ratio on 1997 johnson 150

and what was be the slippage on a 20 ft fish-n-ski with a 150 and a 21 pitch prop

 

[90srtatos]

Re: gear ratio on 1997 johnson 150

anyone know

 

[jy118lfd]

Re: gear ratio on 1997 johnson 150

1.86 to 1

 

[90srtatos]

Re: gear ratio on 1997 johnson 150

thanks jon for the answer

 

[michligj]

Re: gear ratio on 1997 johnson 150

In order to determine slippage, we would need some more numbers: the rpms and accurate mph speed.

 

[90srtatos]

Re: gear ratio on 1997 johnson 150

jm i can run about 51 @ about 5100 rpm

 

[michligj]

Re: gear ratio on 1997 johnson 150

That puts you at about 6.4% slip which is very good. <br /><br />I would bet that you are actually turning just a bit more than 5100rpm and have a slip closer to 8%. Very respectable numbers

 

[TLL]

Re: gear ratio on 1997 johnson 150

Sorry, numbers don't compute.<br />1.89 ratio<br />21 pitch<br />51 mph<br />5100 rpm<br />Equals -3% prop slip - impossible.<br /><br />Rpms or speedometer must be off, Prop slip calcuator shows a max of around 45 mph for your specs. Do you have speed by a gps?

 

[michligj]

Re: gear ratio on 1997 johnson 150

TLL,<br />I'm curious as to which calculator you are using. <br /><br />using 1.86 as the gear ratio (not 1.89 as you stated )<br /><br />I came up with 6.4%<br /><br />Even Plugging in a 1.89 ratio it kicks out 4.9% slip.<br /><br />I agree that some of the numbers can't be totally accurate. I suspect either the speedo is of by a couple mph or the rpms are off by maybe 100 or so. (the original post did say "about 5100 rpms")<br /><br />Changing the rpms to 5200 gives a slip of 8.2% @ 51 mph, which is realistic. <br /><br />I'm using a calculator at the following link, maybe I'll try doing the math myself and see if the calculator is not kicking out accurate figures.<br /><br /> http://www.rbbi.com/folders/prop/propcalc.htm

 

[TLL]

Re: gear ratio on 1997 johnson 150

Whoops, I ment 1.86. I was using the Mercruiser prop slip calcuator. Full out racing boats have to work at achieving values under 10%. Most light fast boats have 10-15% slip. <br /><br />Wouldn't you know I ran the numbers again and came up with 6.5%. Need to get my eyes checked.<br />6.5% is still too good to be true. I would guess that the boat speed is is off a bit.

 

[michligj]

Re: gear ratio on 1997 johnson 150

TLL,<br />Glad to hear that your numbers came in line with what I had. I did the math manually and got the same, So I was relly hoping. <br /><br />stratos,<br />We both agree that your numbers must be off by a little bit. But I wouldn't worry about it. It appears if you adjust the numbers slightly you will easily be below 15%, which is where you want to be.

 

[90srtatos]

Re: gear ratio on 1997 johnson 150

jm ,what change would i get by going to a 24 instead of a 21 , thanks guy for the help and answers,,

 

[Dhadley]

Re: gear ratio on 1997 johnson 150

5100 is lugging the motor now. Going to a higher pitch will only kill the motor sooner.

 

[90srtatos]

Re: gear ratio on 1997 johnson 150

so what pitch do i need to go with

 

[michligj]

Re: gear ratio on 1997 johnson 150

thoeretically, if you can still turn the 24 pitch at 5100 rpm, you could expect around 57mph.<br /><br />The big problem is that you will not be able to spin the 24pitch that fast. You generally lose about 250-300 rpms per inch of pitch increase. That would put you at 3900-4350 which will severely lug your motor and cause some serious problems and only give you about 49mph.<br /><br />So, long story short. Stay with your 21, it seems your setup is where it should be<br /><br />hope that helps

 

[Goodoleboy]

Re: gear ratio on 1997 johnson 150

Its my guess your gona get a blown up motor pretty quick. If you dont get those RPMs up to near 6000. Or at least high fives.<br /><br />I think your motor is lugging even now with the 21 pitch prop. Going to 24 will result in a quicker death of your motor.<br /><br />Drop back to a 20 or even 19 to get those RPMs up. Your prop slip should be someplace close 12 to 15%<br /><br />Your boat speed will remain close to the same as you have now. But your engine will live MUCH longer.<br /><br />Bet ya uh nickel DHadley will tell you something close to what Iam saying. <br /><br />Ive read a hundred of his post, And he never wavires...Get those RPMs up soon!<br /><br />Good Luck!

 

[90srtatos]

Re: gear ratio on 1997 johnson 150

so 50 to about 52 mph is the fastest i can get out of the 150

 

[walleyehed]

Re: gear ratio on 1997 johnson 150

21??? Yea, if we can get the R's up by atleast 500.<br />5100 is gonna smoke'er inside...5500 would be the minumum you want.<br />And just what 21" prop are we using???<br />On a jackplate I assume??

 

[90srtatos]

Re: gear ratio on 1997 johnson 150

its a michagan wheel ss 21 witout a jack plate