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  1. #1
    Mike's GPR's Avatar
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    Summer RPM's (How low is too low?)

    I ran my ski in cooler weather a couple weeks ago and ran a constant 7150rpms on numerous outings. I then went up to Wisconsin last week and the weather was a little warmer and more humid and my rpms went down to 7050. My mods are listed below...


    ???'s
    * I am starting to think I am a little shy on rpm's. Where is the dreaded detonation zone for max rpms?

    * Ideal rpm's are ??? (7150-7200?)

    * Should I keep the Solas concord 14/20 or go back to the 13/19? Any other prop suggestions are welcomed.

    * Typically how many rpms are gained by going from an 85mm nozzle to an 87mm nozzle?
    (not sure how many rpms I gained by boring out my 85mm nozzle to 86.8mm as I did this with a few other mods)

    * (A question was PM'ed to me... Has anyone ever tuned there ski in the cooler weather with an 85mm nozzle and then just switched to an 87mm nozzle in warmer weather to make up the rpm loss?)


    1200 grate
    R&D ride plate (IR mod 4)
    R&D Auto Drop Nozzle & stock steering nozzle (no difference in RPMS)
    4 degree keyway
    stock reeds and no stuffers
    150 psi milled head
    jetworks
    dumping 3rd cylinder water
    Riva Free Flow
    1300r Waterbox
    85mm nozzle bored to 86.8mm
    old style pump with a IR 14/20 prop (measures 13/19 on my guage)


  2. #2
    alex29573's Avatar
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    if rpms are low you will detonate??? oh snap...

  3. #3
    Altezza01's Avatar
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    Jun 2007
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    yes if you're rpms are too low you can detonate and you're overloading the motor. that's why it's critical to have your ski running in the power band usually around 7150-7250.

  4. #4
    Happily Self-Employed WFO's Avatar
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    Quote Originally Posted by Mike's GPR View Post
    I ran my ski in cooler weather a couple weeks ago and ran a constant 7150rpms on numerous outings. I then went up to Wisconsin last week and the weather was a little warmer and more humid and my rpms went down to 7050. My mods are listed below...


    ???'s
    * I am starting to think I am a little shy on rpm's. Where is the dreaded detonation zone for max rpms?

    below 7000

    * Ideal rpm's are ??? (7150-7200?)

    yes, depending on porting and timing

    * Should I keep the Solas concord 14/20 or go back to the 13/19? Any other prop suggestions are welcomed.

    14/20 unless you can get the r's up

    * Typically how many rpms are gained by going from an 85mm nozzle to an 87mm nozzle?

    60-80
    (not sure how many rpms I gained by boring out my 85mm nozzle to 86.8mm as I did this with a few other mods)

    * (A question was PM'ed to me... Has anyone ever tuned there ski in the cooler weather with an 85mm nozzle and then just switched to an 87mm nozzle in warmer weather to make up the rpm loss?)

    yes

    1200 grate
    R&D ride plate (IR mod 4)
    R&D Auto Drop Nozzle & stock steering nozzle (no difference in RPMS)
    4 degree keyway
    stock reeds and no stuffers
    150 psi milled head
    jetworks
    dumping 3rd cylinder water
    Riva Free Flow
    1300r Waterbox
    85mm nozzle bored to 86.8mm
    old style pump with a IR 14/20 prop (measures 13/19 on my guage)
    gimmie a ring if you want to chat about it

  5. #5
    RHeller1's Avatar
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    May 2008
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    I am in the same situation...7050rpm is what I am hitting at max rpm...any quick tips to get the rpm up about 100 rpm?

  6. #6
    All hail the Chief! fullboogie's Avatar
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    Quote Originally Posted by RHeller1 View Post
    I am in the same situation...7050rpm is what I am hitting at max rpm...any quick tips to get the rpm up about 100 rpm?
    Repitch the prop for summer heat. You'll get extra rpms in the winter, but that's not a bad thing.

    Or better yet, have a summer and a winter prop.

  7. #7
    SHOBiz's Avatar
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    Quote Originally Posted by fullboogie View Post
    Repitch the prop for summer heat. You'll get extra rpms in the winter, but that's not a bad thing.

    Or better yet, have a summer and a winter prop.

    +1

  8. #8
    RHeller1's Avatar
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    May 2008
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    Minnesota
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    up here in MN we only have summer... how much change equals about 100rpm?

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