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  1. #1
    MR. SCOVILLE UNIT SUCKMYWAKE's Avatar
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    Choosing The Right Prop

    not all props are the same

    most props are descibed according to the pitch. pitch is the forward movement of the propeller thru one complete revolution. pitch can be thought of as speed. the higher pitch the prop can turn, the faster the boat will usually go.

    what if your engine operates at wrong rpm at wot? pitch and rpm have an inverse relationship. increasing pitch reduces rpm and reducing pitch increases rpm. a 1'' change in pitch will usually result in a 200 rpm change in engine speed. therefore, if your engine operates below the proper rpm, consider a propeller with less pitch. if your engine over-revs, consider increasing the pitch.

    i know, i know, excellent post bri.


  2. #2
    Pistonwash's Avatar
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    1 inch change = 200 rpm? Better go back to math class peanut head.

    I think you meant 1 degree which usually translates into 150 rpm. Other than that good post. Oh yeah...and you are actually trying to "get-on-the-pipe" when you are adjusting your prop pitch. Find the rpm's where the pipe quits making power and that is where you want your prop to be in and around 100 or so rpm's in the +. I'm speaking in general applications, not all.

  3. #3
    MR. SCOVILLE UNIT SUCKMYWAKE's Avatar
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    1 inch change = 200 rpm? Better go back to math class peanut head.

    a 1 inch change, not one degree
    one degree is less of an rpm change ya coconut head
    like going from a 25 to a 23 might be one inch

  4. #4
    MR. SCOVILLE UNIT SUCKMYWAKE's Avatar
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    The last 2 inches of the trailing blade is what you bend to change rpm"s Higher pitch # reduces rpm's lower pitch # increases rpm's A '1' increase in prop pitch trailing end of blade usualy changes 75-100 rpm"s Leading edge pitch changes usualy has to to with acceleration only not max rpm's The lower the # on the leading edge the better acceleration I usualy run a 13 most of the time and change the trailing end to match my desired rpm's I like 7150-7250 on a single pipe ski.

    read above for 1 degree change rpm's i still love ya mikey

  5. #5
    Hydrotherapy's Avatar
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    great info but can you explain how the dyna fly pitch relates to rpm as i'm baffled how i,m going up so high in pitch and still turnig good rpm's,hence thinking i can go at least another 2 degrees then i will be spinning a 25.

    not starting a peanut or coconut head fight just need to learn

  6. #6
    MR. SCOVILLE UNIT SUCKMYWAKE's Avatar
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    i think your mods have given you the extra rpms that you can spin it paul.
    the reeds, the keyway, etc.

  7. #7
    Moderator RX951's Avatar
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    Very Good information Brian !

  8. #8
    Hydrotherapy's Avatar
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    Quote Originally Posted by SUCKMYWAKE View Post
    i think your mods have given you the extra rpms that you can spin it paul.
    the reeds, the keyway, etc.
    got that bit ok brian but this is the wierd bit that dont equate

    spun with all modds a 14/20 box dyna fly pitch checked @ 7240..

    spinning a 14/23 with no more modds @ 7190..

    rpm checked and recorded with pet 2100 and tiny tach running side by side..

    3 degrees on prop and only 50 rpm lost...

    what can i spin to get me to 7150 my ideal rpm ?????

  9. #9
    mtrager's Avatar
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    Salty,

    How props are pitched is the key and who is pitching them. I have lots of props for my single. Some can be used on my triple. I have a 16/25
    that Gpr Pittman pitched that would spin 7180 before my throttle bodies
    were done. I have a Fercho 14/23 that would spin 7300. Both had vey similar performance.

    I have a Scat Swurl impeller that is a 14/28/29 ? the gauge does not go that high. My single pulls no problem. Its who is pitching them not what size they are.



    Jim made me a 13/26 last week which put me over 80 in a short distance.

    My Efi ski has always run fastest in the 7080 to 7100 range.

    All the above are running the 85 nozzell except the Scat. Which I will now try with the throttle body mod.
    Last edited by mtrager; 04-12-2007 at 08:52 AM.

  10. #10
    Happily Self-Employed WFO's Avatar
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    BTW Mark

    While your at it what is your neck and BVD size ???

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