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  1. #1
    JFizzleJR's Avatar
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    Air Intake Vs. Prop Pitch

    Is a different than stock prop pitch needed to accomodate a custom air intake? I ask this because of a simple equation dealing with rpms.
    8100 (stock) + 150-200 = 8250-8300
    rev-limit = 8200 8200+ = banging off limiter without a new prop.
    is the 14/19 the key to the problem for an rxp? the pitch maybe drops the rpms 200 to equalize the 200 rpms gain with the non-restrictive air intake.
    does anybody understand what i'm talking about??


  2. #2
    Ahh....where am I?
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    I comprehend! But I got nothing to add...

  3. #3

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    Well it is possible YES if you are using STOCK ECU. I currently have a Stage 1 that runs around 8120 RPM's . I noticed however that the RIVA intake that comes with the stage 1 kit DID NOT increase my RPMS over stock since it was turning the same rpm with the STOCK intake. Now IF I was using a 4 inch intake setup, it is possible that I could see an increase to 8200-8300 . As horsepower increases so does the ability of the ski to turn the same prop at FASTER rpms. That is why for example the riva stage 2 kit calls for the 15/20 impeller instead of the 14/19 impeller. IF you used the 14/19 impeller with the stage 2 kit your rpms would probably be 8300-8400. Now IF you used the RR 4501 ECU then the rev limiter in THAT ECU is set higher so I know some of the faster guys on the board go this route.

    On a side note, with the RIVA intake it is probably taking in as much air as it can considering it's diameter because when I took the bucket out it still would NOT RPM any higher. I KNOW the 4 inch system will allow the motor to rev higher. Also consider that warmer water like what I run in (84-88 degrees) is limiting RPM to a certain extent also.

    So as we get COLDER weather, the RPM on these skis will get higher so some of the guys that are marginally high now may start to hit off the rev limiter.

  4. #4
    Site Admin Green Hulk's Avatar
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    Quote Originally Posted by Schlonky1
    Is a different than stock prop pitch needed to accomodate a custom air intake? I ask this because of a simple equation dealing with rpms.
    8100 (stock) + 150-200 = 8250-8300
    rev-limit = 8200 8200+ = banging off limiter without a new prop.
    is the 14/19 the key to the problem for an rxp? the pitch maybe drops the rpms 200 to equalize the 200 rpms gain with the non-restrictive air intake.
    does anybody understand what i'm talking about??
    You got it! When going with a better air intake such as the Riva you get the most benefit by going to a steeper pitch. The 14/19R fits the bill on your setup.

  5. #5
    Will work on YOUR ski for FREE! GeoRXT's Avatar
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    What happens when you hit the rev limiter? Does it loose power? Does it just keep going up and down to the limiter?

  6. #6
    JFizzleJR's Avatar
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    Quote Originally Posted by GeoRXT
    What happens when you hit the rev limiter? Does it loose power? Does it just keep going up and down to the limiter?
    i'm pretty sure both happen at the same time. When it hits the limiter you lose power from the rpms suddenly dropping. Then you have surges upward and hit the limiter. But the power surges aren't too out of control, you won't fly off your ski. It's just bad for the ski.

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