User Tag List

Page 1 of 2 1 2 LastLast
Results 1 to 15 of 21
  1. #1
    Join Date
    May 2010
    Location
    Germany
    Posts
    15
    Thanks (Given)
    9
    Thanks (Received)
    0
    Likes (Given)
    5
    Likes (Received)
    5
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Effect by shortening the shaft of an 2 stroke outboard

    Dear all,

    i tried to find an answer on the internet but can't get one.

    Wich effekt does it have on a 2 stroke when i shorten the aluminium housing (shaft) where the exhaust pipe is sitting in. The exhaust pipe ist just cylindrical with an open end. So no tuner there. Does the motor extremly change in power when the backpressure is influenced by a modified housing with less volume?
    I see i.e. mercury racing motors with ultra short shafts. They should have a similar problem...

    Dont start loughing, but i like do this to a 3HP Yamaha Malta.

    DIY dyno is already finished;-)

    https://www.youtube.com/watch?v=W6F1K8IYDhM

    Any answers are highly appreciated!

    Thx
    Oliver

  2. #2
    Join Date
    Dec 2001
    Posts
    5,271
    Thanks (Given)
    0
    Thanks (Received)
    42
    Likes (Given)
    0
    Likes (Received)
    230
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Mostly for lower C/G on fast boats with heavy motors. If your 3 hp is on a canoooe it will flip.....

  3. Thanks ostsideend thanked for this post
  4. #3
    Join Date
    Feb 2009
    Location
    Dunnellon, Fl. / Cincinnati, Oh
    Posts
    193
    Thanks (Given)
    35
    Thanks (Received)
    12
    Likes (Given)
    57
    Likes (Received)
    73
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    No laughing here. You sure seem pretty passionate about what you got going on..... Wish I could be more help. I'm no engineer, nor do I know what the phuck I'm lookin at in the video, but I know MY 3 HP. won't flip MY canoe. Interest is interest and you appear genuinely interested!

  5. Thanks ostsideend thanked for this post
  6. #4
    Join Date
    Dec 2001
    Posts
    5,271
    Thanks (Given)
    0
    Thanks (Received)
    42
    Likes (Given)
    0
    Likes (Received)
    230
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I did not look a video just saying high C/G will tend to unstable canoooe.... Story here...... at a boat race me and someone.... both drinking watching race boats. I was in front watching and Canoooe wiggled..... other drunk fell out of canoooe with out captsizeing... I stayed dry. Canoooe is just a longer canoe .... or I just mis/spell......

  7. Thanks ostsideend thanked for this post
    Likes rochelle howell liked this post
  8. #5
    Join Date
    Jul 2012
    Location
    Huntington, Texas
    Posts
    1,422
    Thanks (Given)
    111
    Thanks (Received)
    105
    Likes (Given)
    741
    Likes (Received)
    471
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I don’t think the weight of a 3hp will cause your canoe to capsize unless you hold it over your head while standing and under way..

  9. Likes ostsideend liked this post
  10. #6
    Join Date
    Dec 2001
    Posts
    5,271
    Thanks (Given)
    0
    Thanks (Received)
    42
    Likes (Given)
    0
    Likes (Received)
    230
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I don't think he has a canoe..... I started that.... C/G thought. Maybe he has a Min=maxx.... who knows.....He might not have a boat. Needs to visit we can give him a ride.....

  11. Thanks ostsideend thanked for this post
  12. #7
    Join Date
    Apr 2001
    Location
    Michigan
    Posts
    13,147
    Thanks (Given)
    78
    Thanks (Received)
    214
    Likes (Given)
    3424
    Likes (Received)
    1930
    Mentioned
    0 Post(s)
    Tagged
    1 Thread(s)
    That's a lot of work for a dyno pull on a drill,

  13. #8
    Join Date
    May 2010
    Location
    Germany
    Posts
    15
    Thanks (Given)
    9
    Thanks (Received)
    0
    Likes (Given)
    5
    Likes (Received)
    5
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)


    Thx for your answers. I am doing this just for fun!

    i do have a Bayliner 285. My small rubberboat with approx. 6 feet length takes me to the coast when anchoring. On this dinghi a light weight Yamaha 3HP dos the job.
    I would like to get the dinghi to plane. (For fun)

    i did a lot of work to sqeeze more HP out of it but i found out that without a Dyno it is almost impossible to have progress. Boat doe not plain jet, so no speed comparerism can be done.
    thats why i did the dyno.

    The Motor dos have Cfk Membran, 11:1 compression ratio, larger kart carburettor, digital inner rotor PVL ignition, slightly changed porting and and and...

    Parallel to this work i think i have to change the motor position as well. For that i will build a combination from a set back and Jack plate. When i do this, the shaft will be way to long.

    There my question comes from. What will happen to the power of an 2stroke outboard when the volume of the area (shaft) where the exhaust gas of an open ended pipe are blown into? (Due to cutting i.e. 100mm out from the shaft length)

    best regards Oliver

  14. #9
    Join Date
    Sep 2001
    Location
    Pekin, IL
    Posts
    7,414
    Thanks (Given)
    175
    Thanks (Received)
    218
    Likes (Given)
    791
    Likes (Received)
    1102
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    From a performance perspective there is very little if any difference. The main gains are as stated above. Center of gravity and less weight.

    Rock
    Team Junk

    No sparkling wiggles in here, only dump truck grinches.

    "Screamin Heathen"

  15. Thanks ostsideend thanked for this post
    Likes ostsideend liked this post
  16. #10
    Join Date
    Dec 2001
    Posts
    5,271
    Thanks (Given)
    0
    Thanks (Received)
    42
    Likes (Given)
    0
    Likes (Received)
    230
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Trying to get 3 hp to plane off.......going to need a Merc lab 5 blade..... HeeHee....Boat might have a hook....going to need some balsa core here.... Smiles...

  17. Thanks ostsideend thanked for this post
  18. #11
    Join Date
    May 2002
    Location
    Victorville ca.
    Posts
    434
    Thanks (Given)
    0
    Thanks (Received)
    23
    Likes (Given)
    2
    Likes (Received)
    57
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    When you are dealing with only 3hp a 20% gain is not much in terms of power but might be noticeable? These kind of projects are fun.

  19. Thanks ostsideend thanked for this post
  20. #12
    Join Date
    Dec 2001
    Posts
    5,271
    Thanks (Given)
    0
    Thanks (Received)
    42
    Likes (Given)
    0
    Likes (Received)
    230
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    More fun would be kg7 with Mk 7 covers......smoking as it goes buy all rich guys yachts....With a R tail...

  21. Thanks ostsideend thanked for this post
  22. #13
    Join Date
    May 2010
    Location
    Germany
    Posts
    15
    Thanks (Given)
    9
    Thanks (Received)
    0
    Likes (Given)
    5
    Likes (Received)
    5
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    3HP does not work, but 6 does

    Click image for larger version. 

Name:	Twin Malta.jpg 
Views:	28 
Size:	120.1 KB 
ID:	422947

    Anf if i don't reach 6HP out of one, i still have a bottle of NOS laying around...

  23. #14
    Join Date
    May 2010
    Location
    Germany
    Posts
    15
    Thanks (Given)
    9
    Thanks (Received)
    0
    Likes (Given)
    5
    Likes (Received)
    5
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    How about this Malta (stage 3 or so) ? Looked, let me say interesting similar to a phallus symbol. But the first section of the tuner was a lot to short.

    Click image for larger version. 

Name:	fertsch totale v re.jpg 
Views:	32 
Size:	66.9 KB 
ID:	422951
    Last edited by ostsideend; 11-09-2018 at 03:36 PM.

  24. #15
    Join Date
    Sep 2008
    Location
    Mass
    Posts
    440
    Thanks (Given)
    0
    Thanks (Received)
    15
    Likes (Given)
    1
    Likes (Received)
    37
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Seen as you're in Germany get an ignitech P1 programmable CDI and hook it up to that pvl. Pvl have no ignition curve as far as I know. With a programmable ignition curve you can tune it for way more torque out of the hole and find the best timing for top speed and power.

  25. Likes ostsideend, Cervelo777 liked this post
Page 1 of 2 1 2 LastLast

Similar Threads

  1. Yamaha 50HP 4-Stroke Used Outboard Boat Motor Engine 20″ Shaft
    By marine planets in forum Outboard Engines
    Replies: 0
    Last Post: 09-23-2017, 10:40 AM
  2. Replies: 0
    Last Post: 04-14-2017, 05:57 AM
  3. A couple more drive shaft shortening questions...
    By Blown Up in forum Technical Discussion
    Replies: 1
    Last Post: 07-25-2011, 01:09 PM
  4. Drive shaft / shift shaft shortening questions.
    By Blown Up in forum Technical Discussion
    Replies: 6
    Last Post: 07-21-2011, 03:00 PM
  5. Shaft shortening
    By TTriton in forum Technical Discussion
    Replies: 29
    Last Post: 12-13-2001, 06:25 PM

Posting Permissions

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