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  1. #1

    Impeller pitch designations

    After measuring and testing several impellers, i have came to the conclusion we need a 3rd number in the pitch designation on impellers. My 15-27 impeller has the last 1-1/4 inch of the trailing edge pitched at 27. Another impeller i tested measured a 14-26 and by the numbers it should have given me more rpms. Quite the opposite is what happened. I lost 50 rpms with it. On closer inspection this impeller was bent to a 14-26 and the difference is the 26 bend goes up a full 2 inches on the trailing edge of the impeller blade.
    Both of these impellers are bent by extremely knowledgeable people, and neither is right or wrong, just a different style to their work.

    So to closer gauge what an impeller is custom bent to, ad a 3rd digit telling the length of the final pitch on the trailing edge.
    Example --- instead of this being just a 15-27, this should be called a 15-27-1-1/4...
    Example 2--- Instead of this being just a 14-26, this should be called a 14-26-2.
    Obviously the length of the final pitch is as/if not more important than the degree of the bend itself, so why not create a numerical designation for it?
    This third digit would ad a new level of accuracy in fine tuning your impeller to match your combo, and would end some confusion on why some impellers dont do what you think they should.
    Ross

    Ross


  2. #2
    Thats a good observation Ross. I have heard several times now that one shops pitch is different than another shops pitch even though the final #s are the same. Neither is right or wrong but just different like you said. It does make it harder to order a certain pitch prop. Im all for a standardized method.

  3. #3
    Who pitched this impellers???

  4. #4
    It doesnt matter who pitched them. No names will be named. Thats not the point. The point is when it comes to custom bent impellers there are many ways the bend can be made, and putting a number on the way its bent will help in its application..

  5. #5
    Dave Sharp dav_dman's Avatar
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    good point. And then you have multipitch, where each blade is independently pitched... And staggered cyl compression and porting , and jetting due to different heat and balance in each cyl...

    a LOT more info could be posted that isn't, imo.

    thx Ross.

  6. #6
    Dav just like engine builders dont post porting specs, people that do props dont post impeller pitching specs eithers. In the worls of high performance, those on top have their secrets, that is just the way it is, that is why we go to the water on the weekends to compete, if everyone had the same there would be no competition.

    Coming back to the impeller pitch, Ross there is more thatn just those 3 numbers, blade height, and setback. There is no way to reproduce a prop just by having these numbers, you can probably get close enough, that is why bsns like Skat Trak digitize an impeller to be able to clone it.
    Last edited by Fercho; 07-03-2007 at 10:19 AM.

  7. #7
    (Coming back to the impeller pitch, Ross there is more thatn just those 3 numbers, blade height, and setback.)

    I realize that. Simply bending the blades to a certain position is what most of us do ourselves. Most of us dont cut blades to attain a certain blade height, or set back an impeller because it takes a machinist to do that. Its just an idea for those who like to share info to do just that. If someone doesnt want to, thats their right as a free american also. And all it takes is a pitch gauge and a caliper to measure whats been done anyway so why not label it to begin with? Just my opinion..

  8. #8

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    From what I've noticed the props can be pitched all over the place in terms of numbers. No two props are identical, depends on how far up the blade they are bent and who is doing it. I've learned its hard to compare other setups and props.

    I've seen single pipes turning big 15-26+ props and only going high 70's. I know of a single pipe that is only turning a little 14/23 and going 83mph+ Whats up with that??

  9. #9
    Quote Originally Posted by Ronn25 View Post
    From what I've noticed the props can be pitched all over the place in terms of numbers. No two props are identical, depends on how far up the blade they are bent and who is doing it. I've learned its hard to compare other setups and props.

    I've seen single pipes turning big 15-26+ props and only going high 70's. I know of a single pipe that is only turning a little 14/23 and going 83mph+ Whats up with that??
    Who is that???

  10. #10
    (From what I've noticed the props can be pitched all over the place in terms of numbers. No two props are identical, depends on how far up the blade they are bent and who is doing it)

    You are exactly right Ron, and thats why i started this post, so maybe we could all learn something, and be aware that the specified pitch doesnt mean that much.

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