Page 1 of 4 1 2 3 ... LastLast
Results 1 to 10 of 39
  1. #1

    Join Date
    Aug 2006
    Location
    Gonzales, La
    Posts
    2,145
    +1
    9

    Prop experts, please help

    In the course of all my turbo testing, I've run into a problem that I can't seem to get my head around.

    Test A:
    10 psi boost, 15/20+1 prop (According to IMPROS, it measured at 15/21 on the pitch block), Riva Grate, Stock nozzle, nose cone installed, tank near empty, 8100 rpm, 77.5 mph.

    Test B:
    11 psi boost, Prop re-pitched to 17/22, Riva Grate, Stock nozzle, nose cone removed, 3/4 tank fuel, 8050 rpm, 73 mph.

    I was able to pull the 17/22 prop past 8000 rpm, which I should NOT have been able to do at that boost level. But why the big speed drop??? I called IMPROS and Dave is stumped too.

    Any ideas???

    I can fab stuff up, make big power numbers, and am pretty good with engine management, but it's humbling to find out I apparently know nothing about jet drives even though I'm a PUMP engineer!!!

    All testing was done with a T3 60 trim turbo, TurboXS intercooler, thru-hull exhaust, stock ECU, and 42 lb/hr injectors.

    Mike
    Last edited by engineermike; 03-17-2008 at 09:16 PM.


  2. #2

    Join Date
    Aug 2006
    Location
    Gonzales, La
    Posts
    2,145
    +1
    9
    TTT

  3. #3
    EZ Dock of Long Island Shibby1485's Avatar
    Join Date
    May 2005
    Location
    Long Island, NY
    Posts
    9,464
    +1
    4
    something sure doesn't add up huh Mike. that's strange!!

    given that greatly increased prop pitch, an extra psi of boost, and nearly the same rpms.. it's evident the ski made quite a bit more power from test A to test B...

    4.5 mph difference certainly is NOT from 50 rpms and 3/4 tank of fuel

  4. #4

    Join Date
    Aug 2006
    Location
    Gonzales, La
    Posts
    2,145
    +1
    9
    Quote Originally Posted by Shibby1485 View Post
    ...given that greatly increased prop pitch, an extra psi of boost, and nearly the same rpms.. it's evident the ski made quite a bit more power from test A to test B...
    I don't think so - I added less than 1 psi boost and the weather was a little warmer, so I think the power was about the same in both tests.

    Soooo. . . same power, more pitch, slightly less rpm (not enough to even consider), and much less speed.

    Mike

  5. #5
    I'm probably overstepping my bounds here...

    What kind of clearance does that prop have with the wear ring?

    Did you by chance try putting the nose back on?

  6. #6
    EZ Dock of Long Island Shibby1485's Avatar
    Join Date
    May 2005
    Location
    Long Island, NY
    Posts
    9,464
    +1
    4
    well i'll give you an example...

    about the most drastic thing one of my skis ever did on me was this...

    i had a stock prop turning 8050 with flashes of 8100 @ 68.3 mph

    i replaced it with a solas prop that had more pitch than a stock prop, and i had a constant 8100 and it went up to 71.1

    and those were two runs about 1 hour apart... took me an hour to davit the ski out of the water, drop it on a dolly, take the pump off, change props, lower it back in the water

    so i guess i had a comparable example where i turned two different pitched props at almost the same RPMs with not an ounce more HP and had 3-4 mph change in 1 hour

  7. #7

    Join Date
    Aug 2006
    Location
    Gonzales, La
    Posts
    2,145
    +1
    9
    Quote Originally Posted by VaRedneck View Post
    What kind of clearance does that prop have with the wear ring?
    Probably on the high side at about .020 radial, but it was the same in both tests.

    Just some food for thought, as with any pump, for the same power input, if you get less liquid hp (less thrust), that means that either a) the pump is cavitating or b) the pump is less efficient.

    Mike

  8. #8

    Join Date
    Aug 2006
    Location
    Gonzales, La
    Posts
    2,145
    +1
    9
    Quote Originally Posted by Shibby1485 View Post
    ... i had a stock prop turning 8050 with flashes of 8100 @ 68.3 mph

    i replaced it with a solas prop that had more pitch than a stock prop, and i had a constant 8100 and it went up to 71.1...
    I suppose that just proves that 2 props can take the same hp to drive, but produce different amounts of thrust, meaning 1 is more efficient than the other. Did I just kill the efficiency of my 15/20 by making it a 17/22???

    Mike

  9. #9

    Join Date
    Jan 2006
    Location
    Rydal, Georgia U S A
    Posts
    3,936
    +1
    14
    Quote Originally Posted by engineermike View Post
    I suppose that just proves that 2 props can take the same hp to drive, but produce different amounts of thrust, meaning 1 is more efficient than the other. Did I just kill the efficiency of my 15/20 by making it a 17/22???

    Mike
    You have a PM regarding this.... YES.

  10. #10

    Join Date
    Jan 2006
    Location
    Rydal, Georgia U S A
    Posts
    3,936
    +1
    14
    Quote Originally Posted by Shibby1485 View Post
    something sure doesn't add up huh Mike. that's strange!!

    given that greatly increased prop pitch, an extra psi of boost, and nearly the same rpms.. it's evident the ski made quite a bit more power from test A to test B...

    4.5 mph difference certainly is NOT from 50 rpms and 3/4 tank of fuel

    If you only knew how many times I've done that

Page 1 of 4 1 2 3 ... LastLast

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. No pressure from fuel pump EXPERTS Please Help!
    By jdjd in forum Polaris PWC Performance
    Replies: 6
    Last Post: 08-13-2011, 11:28 PM
  2. experts please help!!!!
    By mfdkhoff261 in forum 4-Tec Performance
    Replies: 5
    Last Post: 05-01-2010, 03:52 PM
  3. Open loop cooling experts- Please Help
    By Importracer in forum 4-Tec Performance
    Replies: 6
    Last Post: 07-23-2009, 07:55 AM
  4. Prop Confusion Please help
    By zerowake in forum 4-Tec Performance
    Replies: 13
    Last Post: 03-16-2009, 09:17 PM
  5. Installing new prop now. Please help.
    By 04RXP22 in forum 4-Tec Performance
    Replies: 4
    Last Post: 09-13-2007, 07:50 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
  •