Results 1 to 9 of 9

Thread: Mini 105 with 447

  1. #1
    Member fox river rat's Avatar
    Join Date
    Jan 2011
    Location
    Batavia, Illinois
    Posts
    50

    Mini 105 with 447

    A two year project to get this puppy wet. The 447 rebuilt with IVO trimmed to around 59 inches. Revs to nearly 7000 rpm with a 2.58 reduction box. It just doesn't get up and go. I can walk faster. What to do???
    Name:  mini-1stday.jpg
Views: 1495
Size:  47.0 KB
    Name:  mini105-447.jpg
Views: 1604
Size:  94.2 KB

  2. #2
    New Member
    Join Date
    Jan 2012
    Location
    Levy, Fl
    Posts
    35
    This is just my opinion based on my experience and research, not enough displacement for the thrust. Have you tried to plane in shallow water? My 12' x 7' Alumitech with a 35 Briggs, a 1.7:1 belt reduction and a 3 blade 60" warp drive with just driver will plane easily. With another rider I need skinny water or I can quickly snap the rudders back and forth and jump up on plane. I am sure there will be suggestion on this site. On other sites you may get some smarty remarks. Good luck with this project. Your engine is something I am considering for my third mini.

  3. #3
    Administrator Papee's Avatar
    Join Date
    Jan 2008
    Location
    PA/GA
    Posts
    2,721
    What pitch do you have in the prop?
    Please check out our YouTube channel and subscribe! Our YouTube Channel helps fund the site. Check it out at https://www.youtube.com/channel/UCTv...FrJP7yQVFVZnyA


  4. #4
    Fox River Rat

    I would think that motor would push that featherweight boat around just fine. Doesn't that engine produce about 50hp at 7000rpm's? Perhaps your motor is running rich, causing it to bog down or load up as we call it up here, resulting in not producing its rated torque for a given rpm. What exhaust are you using? I can't see it clearly in the pictures....Mine gave me all kind of heartburn until I figured out the snowmobile tuned pipe would not work well on my airboat. Usually with a tuned pipe, there is a 'dead' spot in the rpm band just before the engine 'comes on the pipe' and really screams. Perhaps, in reality, you are not getting past that 'dead' spot.....

    Flathead

  5. #5
    Senior Geezer buster's Avatar
    Join Date
    Dec 2008
    Location
    1540 miles northwest of Miami
    Posts
    1,097
    If you can turn the engine up to 7000 rpm, with a 2.58 reduction, your prop should be turning 2,713 rpm if I figured right. That should be plenty to get up on plane. I have to think your problem is with the prop itself, or something other than the engine. There are a number of things you should check out.

    Good luck, Dave

    BTW, How's it going Flathead, it's about time you came out of hibernation!
    IF YOU WON'T STAND BEHIND OUR TROOPS, THEN JUST STAND IN FRONT OF THEM!

  6. #6
    Member fox river rat's Avatar
    Join Date
    Jan 2011
    Location
    Batavia, Illinois
    Posts
    50
    Well, talking to an aviation friend, I need to adjust the prop so the engine only spins at 64-6500 r's. Pitch is too flat, that is why it's running at 7150. That's suppose to make a big difference. This same engine was flying a plane before I got it, same exhaust, etc. So I should be OK. I'll check back in a couple days.

    Thanks for suggestions.

  7. #7
    Member fox river rat's Avatar
    Join Date
    Jan 2011
    Location
    Batavia, Illinois
    Posts
    50
    BTW—447 is around 39.5HP at 6500 rpm.

  8. #8
    Senior Geezer buster's Avatar
    Join Date
    Dec 2008
    Location
    1540 miles northwest of Miami
    Posts
    1,097
    Sounds to me like prop pitch IS a good place to start!
    Dave
    IF YOU WON'T STAND BEHIND OUR TROOPS, THEN JUST STAND IN FRONT OF THEM!

  9. #9
    Administrator Papee's Avatar
    Join Date
    Jan 2008
    Location
    PA/GA
    Posts
    2,721
    Quote Originally Posted by fox river rat View Post
    Well, talking to an aviation friend, I need to adjust the prop so the engine only spins at 64-6500 r's. Pitch is too flat, that is why it's running at 7150. That's suppose to make a big difference. This same engine was flying a plane before I got it, same exhaust, etc. So I should be OK. I'll check back in a couple days.

    Thanks for suggestions.
    I wouldn't stick to a certain or targeted rpm, you need to find out where that motor likes to be run. I'm sure it's just a matter of getting the pitch set, I was thinking belt slippage until I seen that it's a gearbox.
    Please check out our YouTube channel and subscribe! Our YouTube Channel helps fund the site. Check it out at https://www.youtube.com/channel/UCTv...FrJP7yQVFVZnyA


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
  •