how many rpms?

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hrzracr23

Petty Officer 3rd Class
Joined
Aug 15, 2006
Messages
78
How many rpm is a good place to max out at? I have an older 85 horse evinrude. if you put the hammer down she will max out my tach which goes to 6000 RPM i back it down off but what is a max rpm I can run it at for a longer period of time without hurting anything? thanks~josh
 
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emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: how many rpms?

Your engine was rated to operate between 4500 and 5500 rpm. It makes maximum torque in that range. You probably can safely run it to 56-5700. Your engine will run out of breathing capability over that and the torque band drops. I would go to the next higher pitch prop.
 
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F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,226
Re: how many rpms?

Assuming the tach is correct, that is too much RPMs for an 85. Get some more pitch on the prop and it will not only bring down the RPM, but go faster too.
 
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Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: how many rpms?

We'd aim for 5800 with an average load. But first verify that the tach is correct.
 
O

ob

Admiral
Joined
Aug 16, 2002
Messages
6,992
Re: how many rpms?

I agree with DH on verifying the tach reading.Also if you can provide more info on what boat this engine is pushing and the diameter and pitch prop you are currently running,it would make for more accurate advice.
 
H

hrzracr23

Petty Officer 3rd Class
Joined
Aug 15, 2006
Messages
78
Re: how many rpms?

well the boat is a crestliner crusader 550 17 foot open bow. now at the risk of sounding silly. pitch drop and diameter, what's that? the pitch of the motor to the boat? or maybe the pitch of the motor to the water? and i have no guess for diameter lol sorry if I frustrate ya'll im very very new to boating.
 
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hrzracr23

Petty Officer 3rd Class
Joined
Aug 15, 2006
Messages
78
Re: how many rpms?

oh ps. how do I verify my tach is correct? thanks
 
D

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: how many rpms?

You can have a shop verify the tach. They use a shop tach or a known good one and run the boat and compare.

Pitch is measured in inches. It's how far the prop will move in 1 revolution with no slip. A 19" prop will, theoritically, move forward 19" in one revolution. All props slip so then that becomes a factor.

Diameter is simply the measurement across the circle if you were to draw a circle around the prop at the tip of the blades.
 
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