1988 mercury 90 3cyl redline

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Weston666

Cadet
Joined
Sep 23, 2010
Messages
25
I recently bought a 1988 mercury 90 with powertrim, I'm trying to get the correct prop size and was wondering what the redline was on this motor is, I'm currently hitting 5000 rpms at WOT @ 37 mph. It is on a 18 foot aluminum boat. It has a 19 degree pitch on it now
 
Barnacle_Bill

Barnacle_Bill

Admiral
Joined
Feb 8, 2004
Messages
6,469
Re: 1988 mercury 90 3cyl redline

That motor should run between 5000 and 5500 RPM at WOT.
 
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Weston666

Cadet
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Sep 23, 2010
Messages
25
Re: 1988 mercury 90 3cyl redline

bhile said:
That motor should run between 5000 and 5500 RPM at WOT.
Click to expand...

I though I read somewhere that it was 5500 but I'm just not sure. It runs about 4850 wot right now. Would it be safe to prop down to a 17 degree pitch?
 
1

1nebel0

Chief Petty Officer
Joined
Nov 28, 2005
Messages
512
Re: 1988 mercury 90 3cyl redline

most certainly go down to a 17pitch as you aren't spinning enough..The 17 will put you at a little better than 5000... If you want more and can find one rather than buying one, try a 15 which will put you around 5300...it is trial and error for sure buy you are currently over propped...
 
jerryjerry05

jerryjerry05

Supreme Mariner
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May 7, 2008
Messages
17,926
Re: 1988 mercury 90 3cyl redline

Profile?? Where are U.
Most dealers have some props setting around.They will talk to U and even loan U a prop if they think your gonna buy a new one.
Sounds like the 17 is closer to what U need.Things like load, trim, motor performance help decide what U should use.
An 18ft boat with 3 adults 2 kids 2 coolers 3 dogs and a full tank of fuel will operate a lot different than 2 people and 1/2 tank of fuel.
Figure out the regular load and go from there.I just took a boat to the dump The hull had an extra 600# of soaked foam.Good luck,J
 
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