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  1. #1

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    Prop Pitched Higher - Speed Decrease

    I have been having great luck, having Speedfreaks pitch my prop increasingly higher. It is now a 25, but today my rpms decreased and so did my speed. I lost 100 rpms when it was pitched from a 24 to 25. It is now 7140. I lost .7 mph. The temp was about 15 degrees warmer with a lot of humidity today. Would that make a difference in my speed decrease? We were trying to get the rpm in the 7130-7170 range. I wonder if this is always the range for 1300s?


  2. #2
    ABBOTT's Avatar
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    7150-7200 is the power band for the GPR (single pipe). Anything significantly lower can mean pre-detonation and anything significantly higher, you will be spinning your tires.

    15 degrees - you bet your rear end that made a difference. That may be where all of the speed went. You will have to test when it's identical to what you last ran with on the last pitch you had to know for certain and you will have to do several runs to get the average.
    Humidity matters too along with the pressure, chances are with a 15 degree hike in temp---the humidity went with it and the barometer probably nose-dived to the low 29's.

    Hope that this helps.

  3. #3

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    Yes, that does help. I am going to give it a try this weekend, since the weather is cooling rapidly. Thanks for posting the range. I was hoping to pick up some speed as we decreased my rpms. Thanks.

  4. #4
    Quote Originally Posted by ABBOTT
    7150-7200 is the power band for the GPR (single pipe). Anything significantly lower can mean pre-detonation and anything significantly higher, you will be spinning your tires.

    15 degrees - you bet your rear end that made a difference. That may be where all of the speed went. You will have to test when it's identical to what you last ran with on the last pitch you had to know for certain and you will have to do several runs to get the average.
    Humidity matters too along with the pressure, chances are with a 15 degree hike in temp---the humidity went with it and the barometer probably nose-dived to the low 29's.

    Hope that this helps.
    I run my ski's 7100-7150 RPM

  5. #5
    ABBOTT's Avatar
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    Good deal! Hence the word "significantly" in my post.

  6. #6

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    I'm sure both of your have reasons for running in the rpm range that you have listed. Just curious as to why you've selected those ranges? With the mods listed on my 1300 should I be at the lower or upper level of the range 7100-7200? I appreciate your knowledge.

  7. #7
    Happily Self-Employed WFO's Avatar
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    Being ported with a key and EFI I would shoot for 7140-7180 range. Your timing starts to drop off considerably after 7200 rpms.

  8. #8
    ABBOTT's Avatar
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    Quote Originally Posted by WFO
    Being ported with a key and EFI I would shoot for 7140-7180 range. Your timing starts to drop off considerably after 7200 rpms.
    That is correct.

  9. #9

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    If I am running in between 7100 and 7200 then I am happy.

  10. #10
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    Quote Originally Posted by Fercho
    I run my ski's 7100-7150 RPM
    You rode your ski ?

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