Those with merc 25 2s experience- what was your RPM?

Discussion in 'Outboard Maintenance' started by Dillusion, Feb 22, 2013.

  1. Dillusion

    Dillusion devilray snob

    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.
  2. 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

  3. Dillusion

    Dillusion devilray snob

    Merc goes up to 6000
  4. HaMm3r

    HaMm3r Well-Known Member

    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. ;)
  5. Dillusion

    Dillusion devilray snob

    Dont mind my explanation...whatever a cup does- it's doing it.
  6. HaMm3r

    HaMm3r Well-Known Member

    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.
  7. Creek Runner

    Creek Runner Well-Known Member

    ^ 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!
  8. HaMm3r

    HaMm3r Well-Known Member

    Can't argue with that. Taking gear ratio into account, a 15 or 16 pitch at 5400 rpm would give you a potentially higher top speed than a 13 or 14 at 6000. If you're happy with the low end, then you're done.