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  1. #1
    NoMo-xp4me's Avatar
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    Prop question (root angle Vs. holeshot)

    Just got my 06 Rxp running (4" rear intake, RR s/c wheel, reverse bucket trimmed, 14/19r-stock) again and I am hitting the limiter hard out of the hole. It shoots straight to the limiter on the launch. I just had the carbon seal replaced and there is no water present in the hull.

    I can feather the ski and it launches pretty good, then pulls to 8260 or so (8 hrs). I know I need to tweek my prop, but I'm concerned that I'll still be all over the limiter on the launch.

    Will changing to a 15/20 be necessary, or can I tweek my current setup to get it right? How much would you guys suggest? 2mm or so?

    I've heard that the limiter is higher (8300) on the 06-up models. Do I still need to shoot for 8100-8140/60 rpms, or should I go higher (8200 or so)?

    There are a ton of threads on this I know (searched), but I haven't seen much info on the 06 limiter issue-everyone talks about 8150 rpms or so for the best top speed.


  2. #2
    NoMo-xp4me's Avatar
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    Quote Originally Posted by NoMo-xp4me View Post
    Just got my 06 Rxp running (4" rear intake, RR s/c wheel, reverse bucket trimmed, 14/19r-stock) again and I am hitting the limiter hard out of the hole. It shoots straight to the limiter on the launch. I just had the carbon seal replaced and there is no water present in the hull.

    I can feather the ski and it launches pretty good, then pulls to 8260 or so (8 hrs). I know I need to tweek my prop, but I'm concerned that I'll still be all over the limiter on the launch.

    Will changing to a 15/20 be necessary, or can I tweek my current setup to get it right? How much would you guys suggest? 2mm or so?

    I've heard that the limiter is higher (8300) on the 06-up models. Do I still need to shoot for 8100-8140/60 rpms, or should I go higher (8200 or so)?

    There are a ton of threads on this I know (searched), but I haven't seen much info on the 06 limiter issue-everyone talks about 8150 rpms or so for the best top speed.

    43 Lookers and no replies? No-one knows how much the first number on a prop "14" in 14/19r affects the hook-up of the ski? Do the larger props launch harder if you have the power to turn them?

  3. #3
    AKA: Larry lafjax's Avatar
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    Sorry, I don't know. This prop stuff is still a mystery to me. I just use folks recommendations until I find the right one. On airplanes the first number is the diameter and the 2nd number is the pitch (the number of inches the prop would travel in one reveloution) but evidently that dosen't work here.
    Last edited by lafjax; 05-29-2007 at 01:05 PM.

  4. #4
    The first number is the angle of the front of the blade. This is the hole shot number. The second number is the trailing edge. This is the top end number and how we control RPMs.

    or so I am told

  5. #5
    Moderator The Bandit's Avatar
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    You can add 2mm to the 14/19r and go from there. 06 is a higher limit but you want to be in the 8140-8180 range for max top speed. I experimented with getting the revs higher and I actually went slower.

  6. #6

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    I've wondered about this myself. I actually have a very similar setup (3" intake, RR SC wheel, grate, wedge, free mods) with a 14/19R that was re-pitched by Impros to 15/20R. With a brand new wear ring, it will come close to the limiter but not hit it. As soon as you get a tiny bit of wear in the ring, like 2 or 3 rides, it starts banging the limiter again. Not sure what to do here. . .

    I really think the RXP pump is just too small diameter for the power we're putting to it. It's the same pump that lesser power ski's use (to save money no doubt) and mine seems to be very sensitive to a small amount of clearance. It's probably marginal stock, but when you add 10% power it goes right on the ragged edge. My old HX would run nearly the same with a totally shot wear ring as it would with a new one.

    I imagine these Stage III ski's are all over the limiter out the hole. . . That's why they put in an adjustable venturi I think.

    Mike

  7. #7
    GTXX's Avatar
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    simple answer, usually you're better off taking pitch out of a too big impeller than adding pitch to a too small impeller because of the root angle at the hub. If your blowing out the 14/19 from a dead stop, get the 15/20 and take some out of the trailing edge if needed to adjust your max rpm, it will launch better

  8. #8

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    I was split between the 14/19R and the 15/20R since I'm only at Stage 1+, which falls between the 2 props according to Riva. Ask ou812 about the dozen or so PM's between us discussing this. . . Anyway, I thought that the 14/19 re-pitched to 15/20 would be the hot ticket for me, and it is as long as my wear ring is perfect. . .

    Mike

  9. #9

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    Quote Originally Posted by GTXX View Post
    simple answer, usually you're better off taking pitch out of a too big impeller than adding pitch to a too small impeller because of the root angle at the hub. If your blowing out the 14/19 from a dead stop, get the 15/20 and take some out of the trailing edge if needed to adjust your max rpm, it will launch better

    That sounds and works good on 4 blades... the new 3 blades are REAL tough to bend the leading edge.

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