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  1. #1
    DaveC's Avatar
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    RXP lowered performance

    I had the Riva stg. 1 with a Rotax Racing SC impeller, skegs and holes filled etc. with a best of 8120 RPMs and 74.1 mph

    Now I have this,


    Riva parts-rear air, adjustable nozzle with 81mm ring,intake grate, 2* wedge, intercooler w/metal pipes and no BOV, SC washers,SS wear ring,
    Rotax parts- SC impeller and thermostat. Also have Piranha front motor mount and exhaust hose without resonator. Solas 15/20R, RE OPAS blockoffs, 42# injectors, Groco strainer,oil catch can,ride plate holes filled, GH skegs and reverse bucket trimmed.

    This has resulted in 67.3 at 7400-7500 RPMs. Not sure where to start, I checked for boost leaks and removed/cleaned then re-installed the inlet and outlet pipes for the intercooler. If felt faster but had the same speed.

    I am going to add the SC3 but wanted to check the difference with the RR impeller, performance was down so much I have opted to attempt to trouble shoot the problems first.

    Any ideas appreciated,
    Dave


  2. #2
    JFizzleJR's Avatar
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    Who did the supercharger service?
    If it wasn't someone reputable, the washers on your shaft could be the wrong year.
    What pitch prop did you have before?
    The 15/20 you have now, is it out of the box pitch?
    Do you have a boost gauge?

  3. #3

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    I'd say it's a charger issue and /or 81mm ring 15/20 combo not enough thrust.

  4. #4
    Quote Originally Posted by DaveC View Post
    I had the Riva stg. 1 with a Rotax Racing SC impeller, skegs and holes filled etc. with a best of 8120 RPMs and 74.1 mph

    Now I have this,


    Riva parts-rear air, adjustable nozzle with 81mm ring,intake grate, 2* wedge, intercooler w/metal pipes and no BOV, SC washers,SS wear ring,
    Rotax parts- SC impeller and thermostat. Also have Piranha front motor mount and exhaust hose without resonator. Solas 15/20R, RE OPAS blockoffs, 42# injectors, Groco strainer,oil catch can,ride plate holes filled, GH skegs and reverse bucket trimmed.

    This has resulted in 67.3 at 7400-7500 RPMs. Not sure where to start, I checked for boost leaks and removed/cleaned then re-installed the inlet and outlet pipes for the intercooler. If felt faster but had the same speed.

    I am going to add the SC3 but wanted to check the difference with the RR impeller, performance was down so much I have opted to attempt to trouble shoot the problems first.

    Any ideas appreciated,
    Dave
    Sounds exactly like the problem I had a month or so ago. You say you checked for boost leaks in the pipes connecting the SC, IC, and TB but have you checked the stock IC blockoff? How well did you seal it with silicone? I noticed that a small bead will not do the job.

    How is the acceleration and hole shot? Is it snappy or noticably different than before or is the ski acting sluggish?

    Also, how many hours are on your SC since you upgraded the washers and how hard do you ride the ski? Your clutch could be starting to slip earlier now.

  5. #5
    Dont judge me...
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    that sounds like a boost leak to me as long as the sc and everthing is put together right.

  6. #6
    REID2168's Avatar
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    is the PIRAHNA MOTOR MOUNT the SAME height as STOCK??????? if NOT u could have DRIVELINE BIND!!!!!!!!!!!!!! causing RPM LOSS AND SPEED LOSS IMMEDIATELY!!!!!!! i already watched my buddy do it to his boat with the ROTAX mount it was 2mm shorter than the STOCK MOUNT!! i said NO he did it ANYWAY WITHOUT SHIMMIMG THE MOTOR BACK AND lost 3MPH PERIOD! most skis DONT HAVE GREAT DRIVELIVE ALIGNMENT TO BEGIN WITH and if u alter it EVEN MORE THE WRONG WAY IT IS GOING TO EFFECT YOUR SKI BIGTIME! PERIOD!

  7. #7
    REID2168's Avatar
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    as well TODAY i watched BOB!(** run his SOLAS 15/20R and LOST 200 RPM over RIVA 15/19R but picked up 1 MPH when we changed it out! BOTH THOSE COULD BE POTENTIAL effects to your SITUATION. just my thoughts good luck!!!!!!!!!!

  8. #8
    DaveC's Avatar
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    JFizzle,

    Jerry did the SC and of course it appears correct. I had the 14/19R from the Stg. 1 kit and the 15/20R is out of the box.

    I have a dynotune gauge and it was showing 7-7.5 psi. The gauge seemed to act a little funky to me, perhaps just the way they work.
    Jerry has made a few suggestions that I am checking now, I will report back soon as completed and tested.

    thanks,



    Quote Originally Posted by JFizzleJR View Post
    Who did the supercharger service?
    If it wasn't someone reputable, the washers on your shaft could be the wrong year.
    What pitch prop did you have before?
    The 15/20 you have now, is it out of the box pitch?
    Do you have a boost gauge?

  9. #9
    DaveC's Avatar
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    I am checking the TB andd stock IC blockoff again. I used silicone on the blockoff during install perhaps I did not use enough for a good seal. Are you applying the silicone on the O-ring or just closer to the edge where it fits up against the intake ? Is there a problem using teflon tape on the sending unit for the Dynotune gauge ?

    The throttle response does not feel that bad, just does not have the pull it used to. It has 13 hours total on the SC. Most of the time I would say that it is ridden between 3500-6500 RPMs along with a few WOTs approx. 1/4 mile long max.







    Quote Originally Posted by RXPkid View Post
    Sounds exactly like the problem I had a month or so ago. You say you checked for boost leaks in the pipes connecting the SC, IC, and TB but have you checked the stock IC blockoff? How well did you seal it with silicone? I noticed that a small bead will not do the job.

    How is the acceleration and hole shot? Is it snappy or noticably different than before or is the ski acting sluggish?

    Also, how many hours are on your SC since you upgraded the washers and how hard do you ride the ski? Your clutch could be starting to slip earlier now.

  10. #10
    Quote Originally Posted by DaveC View Post
    I am checking the TB andd stock IC blockoff again. I used silicone on the blockoff during install perhaps I did not use enough for a good seal. Are you applying the silicone on the O-ring or just closer to the edge where it fits up against the intake ? Is there a problem using teflon tape on the sending unit for the Dynotune gauge ?

    The throttle response does not feel that bad, just does not have the pull it used to. It has 13 hours total on the SC. Most of the time I would say that it is ridden between 3500-6500 RPMs along with a few WOTs approx. 1/4 mile long max.
    Don't apply it to the o-ring. just apply it to the mating surface where the blockoff mates up against the intake manifold. I decided to fill my u-clamp that holds the blockoff in place with silicone too for extra insurance. It makes a little mess, but I felt it was worth the extra insurance.

    If it does not have the pull it used to then there is most likely a boost leak. After going stage 2 my holeshot was worse than a stock RXP. After reinstalling the blockoff and pipes and sealing them all well my holeshot and acceleration throughout the RPM range were night and day.

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