max rpm's?

[mattttt25]

well, i just started to try and absorb as much info as i can from my new shop manual. talk about detail! anyway, for my engine - 1998 johnson 150 hp oceanrunner - it states max rpm's should be 4500 - 5500. seems like a large range. last time on the water, at calm seas and good trim, i maxed at 4600 and was thinking of re-proping. but i meet their range. what do you guys think??? thanks-

 

[angus63]

Re: max rpm's?

Drop at least 2" in pitch. Your motor will thank you. My 95 175hp evinrude WOT is 5300 and I'm going to drop 1" this year.

 

[Dhadley]

Re: max rpm's?

You are at least 1000 rpm short. That will wear out a motor very quickly. Shoot for 5800 to 6000 with an average load.<br /><br />Rather than drop in pitch I would fine tune the set up. Try to pick up as much rpm as possible by playing with the X dimension and your existing prop. You have your baseline - make ONE change at a time and test under (as close to) the same conditions each time. Test with your average load and in typical water conditions.<br /><br />Just curious - are you sure the tach is correct? Make sure its set on position 6. It may pay in the long run to have it checked aginist a known accurate tach.<br /><br />Good luck!

 

[mattttt25]

Re: max rpm's?

so you're telling me the shop manual (clymer) is wrong??? i'll check the tach position, but not sure how else to test unless i replace. i do plan on fine tuning the set-up, ensuring the throttle linkage is correct, etc. the question had more to do with what the manual is telling me...

 

[wilde1j]

Re: max rpm's?

You could check the tach against a shop tach to verify your own. Dhadley is correct in suggesting 5800 to 6000 RPM and recommending that you get everything else optimized before you start changing prop pitch. Get the motor as high as possible w/o cavitating in turns excessively.<br /><br />Bottom of the RPM range is NG.

 

[mattttt25]

Re: max rpm's?

thanks guys.<br /><br />hey JB, ancient mariner/4-star admiral/old salt, you have an opinion? is the manual off when it recommends 4500-5500 rpm?

 

[mattttt25]

Re: max rpm's?

^

 

[ob]

Re: max rpm's?

matttt25,Rather than implying to prop your motor where it will only be capable of the stated rpm with a given pitch ,it is rather meant as a guideline of Wot operation.It is not advisable to operate said engine above the recommended range for sustained periods.As Dhadley suggests,prop it to turn at the upper range or slightly above ,and operate it within the parameters of the stated range at WOT.Your motor will last longer and throttle response will be crisper.My engine is rated at 5500 to 6000 and is capable of 6200. However only for brief periods does it see 6200 before I throttle back to the recommended range.Propping as such will also accomodate situations of increased payload such as added occupants or skiing.

 

[mattttt25]

Re: max rpm's?

thanks ob, makes sense. i'll try to tune and prop it to run at 5500. that's if this weather ever breaks.