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devilray snob
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Discussion Starter · #1 ·
As the title says, was the most efficient/highest/best spot/etc to get your RPM's at on your merc 25 2s?

My tinytach (accurate) is showing about 5300-5400 WOT with a 15 pitch SS prop cupped down to almost 14p on mine...seems like I can get a little more RPM out of her. Holeshot is good, no pushing/pulling at WOT, not blowing out...

I know that higher RPM != better performance. Just looking to see where others are at.
 

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904 Redfish
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605 Posts
I have almost the same setup on my boat being a shadwocast 16 with johnson 25 with a powertech sra3 in 15 pitch but I have mine double cupped but I am getting around 5450 solo and 5300 with two people and full gear. So that rpm range sounds about right. But for my motor the prm range is 4500-5500 idk if mercs is higher then that
 

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... a 15 pitch SS prop cupped down to almost 14p on mine...
What does this mean? I'm certainly no prop expert, but adding cup typically makes the prop perform as if it were a higher pitch, not lower. Maybe you had some cupping taken out?

At any rate, with my Merc 25 2-stroke and a 4 blade, 14 pitch with heavy cup added, I run around 5900 rpm. Although, the fastest I ever went was when I pushed it to 6170. Won't make a habit of that though. ;)
 

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devilray snob
Joined
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2,398 Posts
Discussion Starter · #5 ·
... a 15 pitch SS prop cupped down to almost 14p on mine...
What does this mean? I'm certainly no prop expert, but adding cup typically makes the prop perform as if it were a higher pitch, not lower. Maybe you had some cupping taken out?

At any rate, with my Merc 25 2-stroke and a 4 blade, 14 pitch with heavy cup added, I run around 5900 rpm. Although, the fastest I ever went was when I pushed it to 6170. Won't make a habit of that though.  ;)
Dont mind my explanation...whatever a cup does- it's doing it.
 

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... a 15 pitch SS prop cupped down to almost 14p on mine...
What does this mean? I'm certainly no prop expert, but adding cup typically makes the prop perform as if it were a higher pitch, not lower. Maybe you had some cupping taken out?

At any rate, with my Merc 25 2-stroke and a 4 blade, 14 pitch with heavy cup added, I run around 5900 rpm. Although, the fastest I ever went was when I pushed it to 6170. Won't make a habit of that though.  ;)
Dont mind my explanation...whatever a cup does- it's doing it.
LOL...ok. ;)

So, if you started with a 15 pitch and had cup added, that prop may be closer to a 16p. Since you're 500-600 below your optimal RPMs, you should be able to drop down at least two inches in pitch. Each inch will roughly increase RPM by about 200, so a 14 pitch or a 13 with extra cupping might be perfect.
 

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... a 15 pitch SS prop cupped down to almost 14p on mine...
What does this mean? I'm certainly no prop expert, but adding cup typically makes the prop perform as if it were a higher pitch, not lower. Maybe you had some cupping taken out?

At any rate, with my Merc 25 2-stroke and a 4 blade, 14 pitch with heavy cup added, I run around 5900 rpm. Although, the fastest I ever went was when I pushed it to 6170. Won't make a habit of that though.  ;)
Dont mind my explanation...whatever a cup does- it's doing it.
LOL...ok.  ;)

So, if you started with a 15 pitch and had cup added, that prop may be closer to a 16p. Since you're 500-600 below your optimal RPMs, you should be able to drop down at least two inches in pitch. Each inch will roughly increase RPM by about 200, so a 14 pitch or a 13 with extra cupping might be perfect.
^ correct adding cup increases pitch or rake depending on where its added.

Your getting your best performance already leave it alone!

Higher RPM does not mean better performance, just as adding cup doesn't decrease pitch.

Cup added to the trailing edge increase pitch, to the tip increases rake!
 
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