1990-91 Force 90 HP recommended WOT RPM's

The Force power

The Force power

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I've been going through a lot of old posts and find various Max RPM's for this motor.
What is the MAX recommended RPM for a '91-'92 / 90 hp Force?

Many thank in advance
 
N

Nordin

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Specs from service manual OB4642 1988 thru 1991 A models says 1990 B 1991 A model 90Hp at 5250 RPM.
Recommended range 5000-5500 RPM, soo I think 5500 RPM is about maximum.
This is the one with 3,375 in bore.
The earlier 85Hp and 90Hp 1990 A model with 3,312 in bore are rated at 5000 RPM and recommended range 4500-5500 RPM.
 
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The Force power

The Force power

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Nordin said:
Specs from service manual OB4642 1988 thru 1991 A models says 1990 B 1991 A model 90Hp at 5250 RPM.
Recommended range 5000-5500 RPM, soo I think 5500 RPM is about maximum.
This is the one with 3,375 in bore.
The earlier 85Hp and 90Hp 1990 A model with 3,312 in bore are rated at 5000 RPM and recommended range 4500-5500 RPM.
Click to expand...

Thank you Nordin,

I'm am a little hesitant to have it screaming at 5,500 but if that's what it is. good to know.
I may stay around 5000 or so (I don't want to blow up this motor)
 
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Nordin

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I agree with you and remember that these engines are about 30 years old and older.
Handle them with care and do not "run the hell out of them".
Then they will last for a very long time.
I run my OB:s at about 3/4 throttle at maximum, sometimes at full throttle for a very short time.
 
jerryjerry05

jerryjerry05

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My twin 88/85hp seemed to run best at about 3800-4400.
and max was about 5300
The right propeller will make a lot of difference.

The boat 88 with twin 85hp came with 17p Alum. props.

I wanted more, so I got a pair of 19p alum.
I got more, about 2-3mph more and my fuel usage went up(more) by about 15-20%.
The rpm's dropped about 300-400
I changed back real quick.
 
nalegtx149

nalegtx149

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i keep my 99 Force 75 at 3/4 most of the time....very rare do i ever full throttle it. Just like most small engines high constant RPM's are a death sentence
 
The Force power

The Force power

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jerryjerry05 said:
My twin 88/85hp seemed to run best at about 3800-4400.
and max was about 5300
The right propeller will make a lot of difference.

The boat 88 with twin 85hp came with 17p Alum. props.

I wanted more, so I got a pair of 19p alum.
I got more, about 2-3mph more and my fuel usage went up(more) by about 15-20%.
The rpm's dropped about 300-400
I changed back real quick.
Click to expand...

Now that I (finally) have a Tach. in the dash, I can start playing with the props.
I'll shoot for 4,500 to 5000 max at Wot & hope for the best.
 
nalegtx149

nalegtx149

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may the force be with you said:
HEY,
Thanks for looking, yeah there are lots of "samples" out there.
I'd like to know for my year of the motor ,in the meantime I'll keep sorting through the archives
Click to expand...

Do you know which ignition system you have? Thunderbolt or Prestolite? ci (CC) are also different, check your engine ID label

1990A 72.4ci (1186.6cc) Prestolite listed at 4500-5500
1990-96 75.2ci (1232.5cc) Thunderbolt listed 5000-5500 cubic inc
 
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