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  1. #1
    oz_speed's Avatar
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    Nozzle Ring Size

    I am looking for a good start point with a Riva Pro Reduction Nozzle. I just have the OEM nozzle on now.

    Can anybody tell me the size of the OEM nozzle? Engine RPM is around 8350-8400 now on good flat water. I am really looking at getting another 100-150rpm out of the ski. I believe moving one size of ring makes around 50rpm is this correct. Looking on the Riva site they recommend a 82mm ring but that is when fitted with a 15-19R

    Mods as below

    RXP
    X-Charger
    Riva ECU
    50 Injectors
    Fizzle intercooler
    3" Riva air intake (soon to be rear air)
    15-22R
    Plastic ring
    R&D Pump cone
    Riva intake grate
    Riva ride plate

    A few other mods but nothing which will effect engine performance.


  2. #2
    Vern's Avatar
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    Nothing wrong with the stock nozzle on your setup. First put on the rear air ... you might get all the rpms you want from that, gaining 100+ rpms with that is not unusual. After the rear air is on, if you still need rpms, you would be best off to tweak the trailing edge of your impeller rather than mess with getting a nozzle. Almost all the nozzle rings are SMALLER, reducing rpms, so I would not change nozzles in your setup.

  3. #3
    oz_speed's Avatar
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    Quote Originally Posted by Vern View Post
    Nothing wrong with the stock nozzle on your setup. First put on the rear air ... you might get all the rpms you want from that, gaining 100+ rpms with that is not unusual. After the rear air is on, if you still need rpms, you would be best off to tweak the trailing edge of your impeller rather than mess with getting a nozzle. Almost all the nozzle rings are SMALLER, reducing rpms, so I would not change nozzles in your setup.
    Do you know size of the OEM nozzle.

    My set up is not much different to the RXP-X set up other that I have the Riva ecu. Riva say you should use the the 82mm ring the stage 1 kit and as my set up is very similar to the Riva stage 1. My thinking was if I went up to a 83mm ring I would gain around 100rpm or am I was off on this?


    Any input on this would be appreciated.

  4. #4
    Moderator Snoman's Avatar
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    215 HP OEM nozzle is 83 mm....
    X-boats OEM nozzle is 87 mm...

  5. #5
    Bob 1tommygunner1927's Avatar
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    Stock reduction nozzle (venturi) is 87mm & each ring, in decending order, will reduce rpm approximaetly 40-50 rpm, according to my findings on my RXT-X. Your venturi is smaller & results may differ.

  6. #6
    CHAD IBADTON's Avatar
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    Rxp stock size is 83

  7. #7
    Bob 1tommygunner1927's Avatar
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    I stand corrected, but the rpm changes will be similar.

  8. #8
    oz_speed's Avatar
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    I am going to be fitting a new S/C something like a Mini Rude or a Rude 2 after the summer so I will be looking at a new impeller then I would think so for now I would prefer to not re-pitch the impeller.

    For now if I fitted a 84mm ring and fitted the rear air kit from what you are saying I should gain around 150-200rpm and a faster pick up.

    Slightly off topic but can anybody also tell me what size spacer I should be looking at fitting under my Riva ride plate to help keep the front end down.

  9. #9
    Moderator Snoman's Avatar
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    With the Riva ride plate .020 seems to be the sweet spot,BUT every boat differs so you may or may not need that much..you will have to "Tune" your ride plate to your boat....

  10. #10
    oz_speed's Avatar
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    Quote Originally Posted by Snoman View Post
    With the Riva ride plate .020 seems to be the sweet spot,BUT every boat differs so you may or may not need that much..you will have to "Tune" your ride plate to your boat....
    Am I right in thinking 0.20 inch is around 5mm. To fit is it just a case of taking the plate off and refitting and sealing with the 0.20 spacer washers between the plate and the hull on the rear two mounting bolts.

    Do you think I will be about right with the 84mm ring and rear as a good starting point to gain 150-200 rpm.

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