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  1. #1
    rick xp's Avatar
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    RXP Nozzle Sizing

    Hey guys,

    Im just trying different nozzle combos on my ski at the moment.

    My results so far have showed that every 1mm decrease in nozzle size is 1 MPH faster.

    -1mm venturi size = 1 MPH top end.

    I tested the 81mm, 80mm and 79mm nozzle and turned the prop to 8500 everytime and i saw a gain of 1 MPH per 1mm reduction. It obviously took a bit more boost to get there but this was tested in the same hour, water, fuel, etc.


    How small can you go before you start getting too much back pressure in the pump?

    Would it be wise to try 77mm or 78mm?


  2. #2
    rick xp's Avatar
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    Bump!

    Does anybody have any info regarding this?

    I have tried the 79mm reduction ring and i was actually getting back pressure back through the bailer tubes.

  3. #3
    Got Boost? psycho rxp's Avatar
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    I usually don't go smaller than an 80mm, because it gets too sluggish off the line. And only use a 79mm ring to choke it off the limiter for a ride till I add pitch, or larger prop.. 81mm seems the sweet spot before adding pitch for me.

  4. #4
    ROTAX RACING performance
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    do run more prop pitch at 81 mm, is sure faster then a smaller prop at 79 mm !

    if you turn up the boost , and would increase the pitch insted of decrease the nozzle, you would get faster as well

    with turbo setup and only 8500 RPM Limiter, you are allways in the Limiter, and you allready run a big prop so degreasing the nozzle is a solution to get of the Limiter at more boost , but that is not optimal for speed, ( accelleration is complete gone at 81 or smaller )

    with 79 mm the overall performance is very poor !

  5. #5

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    Quote Originally Posted by rick xp View Post
    Hey guys,

    Im just trying different nozzle combos on my ski at the moment.

    My results so far have showed that every 1mm decrease in nozzle size is 1 MPH faster.

    -1mm venturi size = 1 MPH top end.

    I tested the 81mm, 80mm and 79mm nozzle and turned the prop to 8500 everytime and i saw a gain of 1 MPH per 1mm reduction. It obviously took a bit more boost to get there but this was tested in the same hour, water, fuel, etc.


    How small can you go before you start getting too much back pressure in the pump?

    Would it be wise to try 77mm or 78mm?
    IF do you us smaller ring in nose you will be much more steering leak.
    Else which setup you like us 77mm ring??

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