RPM’s

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user 21074

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I have a 1985 Johnson 20 hp converted to 30hp.I did have it as a 25 for awhile With an intake swap and found the parts needed to go to 30hp.Prior to conversions I was running approximately 6k according to tiny tach I finally put on.I new it seemed high just by ear.Repiched prop from 11 to 13 and running about 5500 to 5600 as a 30 hp.According to specs I believe 5500 is WOT unless I got wrong info?How detrimental is it to run at higher rpms if I decide to maybe go back to a little higher rpms?
 
Speed is 24mph at 5600 and 27/28 at 6000. Not really too concerned about either speed or hole shot.Just wondering if going over recommended RPM rating by a few hundred is a big deal?Not worth blowing a motor to gain acouple mph. Intake and carb from donor 30hp.
 
The max RPM is published, should be able to find it on the 'net easily. I wouldn't purposefully go over that, you will shorten the motor life.
 
CedarRiverScooter said:
The max RPM is published, should be able to find it on the 'net easily. I wouldn't purposefully go over that, you will shorten the motor life.

Yes.I am prettty sure it is 5500 when I searched for it.Once I repitched the prop It sounded better of course due to the rpm drop.I do miss the extra few mph though :cry:
 
I dont think 6K is "Out of bounds" so to speak, but if youre hitting that with the 13" prop move up to a 15" and you most likely will have the best of both worlds. (ETA, I misread your initial post)

The motor rating is at 5500rpm, ie that is where it theoretically should make the rated HP. It should be electronically governed at 6100 or not at all.

Look on your power pack, if it says 6100 youre governed, if not then you have no governor.
 
Thanks..Prop diameter is the same just the pitch was changed from OEM 11 to 13..Which is what dropped the rpms
 

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