Results 1 to 7 of 7

Thread: Impellers, RPM and other voodoo

  1. #1
    Member Yukoner's Avatar
    Join Date
    Aug 2007
    Location
    Whitehorse Yukon
    Posts
    1,340

    Default Impellers, RPM and other voodoo

    My Evinrude/BRP FICHT 115 is supposed to have 5750 RPM WOT.
    Right now, i'm pulling ~5200 WOT.
    Brand spankin new 4 blade stainless impeller with a "C" forged on it.
    Any idea who makes this impeller and the pitch? Would the fact that its a 4 blade be the cause of the drop in my WOT RPM? Should i care
    Runs great, lots of oomph.
    Thanks all
    Paul

  2. #2

    Default

    The loss of some RPM's going to a stainless 4 blade vs an aluminum 3 blade is not unusual. The stainless has an additional blade and is heavier. You could go to a stainless with less pitch to get your RPM's back. I don't know how that would affect the overall performance of your motor.
    From what i've heard a general rule of thumb is:
    80 HP and less stay with aluminum
    90-120 can go either way
    over 120 hp go stainless

    Just what I've been told. Hope it helps.

  3. #3
    Member Yukoner's Avatar
    Join Date
    Aug 2007
    Location
    Whitehorse Yukon
    Posts
    1,340

    Default

    Thanks for the info.
    It would be nice to see HP, thrust and RPM all plotted on the same graph with different impellers on the same engine, just to see.

  4. #4
    Member
    Join Date
    Apr 2006
    Location
    chugiak, ak
    Posts
    630

    Default Merc

    I got the optimax 150hp. And that is exactly what mine did, i talked to a few shops, and they said i was right were I was supposed to be. So it sounds like you are where you are supposed to be also. Give A1 prop a call in anchorage, they seem to know what they are talking about.

  5. #5
    Member Akgramps's Avatar
    Join Date
    Apr 2008
    Location
    Last civilized place on the planet
    Posts
    2,077

    Default

    On a jet drive OB 5200-5300 rpm would be about right, if you start seeing max rpm it would mean its time to reshim the impeller or replace the cone or both.

  6. #6
    Member
    Join Date
    Sep 2007
    Location
    Fairbanks
    Posts
    65

    Default

    In my limited experience, a properly adjusted impeller, of either kind, will limit RPM to around 5200. As the impeller and sleve wear, RPM will gradually climb.
    When it passes 5,600 RPM, it is time to move a shim from the bottom to the top. This will cause the RPM to drop to around 5,000 t0 5,200, indicating a properly adjusted impeller.
    When all the shims are on top, it is time for either a new liner, new impeller, or both.
    BTW, with the rocks I chew, I never get to use all the shims.
    PS; You are looking for the maximum efficiency of the impeller, not peak hp from the motor.

  7. #7
    Member Yukoner's Avatar
    Join Date
    Aug 2007
    Location
    Whitehorse Yukon
    Posts
    1,340

    Default

    Quote Originally Posted by snowtigger View Post
    In my limited experience, a properly adjusted impeller, of either kind, will limit RPM to around 5200. As the impeller and sleve wear, RPM will gradually climb.
    When it passes 5,600 RPM, it is time to move a shim from the bottom to the top. This will cause the RPM to drop to around 5,000 t0 5,200, indicating a properly adjusted impeller.
    When all the shims are on top, it is time for either a new liner, new impeller, or both.
    BTW, with the rocks I chew, I never get to use all the shims.
    PS; You are looking for the maximum efficiency of the impeller, not peak hp from the motor.
    Pretty much what i had been thinking, but good to here it from other sources.
    Cheers
    Paul

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •