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Thread: RXT Low RPM

  1. #1

    RXT Low RPM

    Here's the story Fellas:

    Last summer I was turning 8060 RPM and 70 MPH with the following set up:

    RIVA Stage I kit
    RIVA / Vortech 'GEN-2' Supercharger Impeller
    RIVA Supercharger Blow-off Valve Kit

    Last ride of the summer my RPM had dropped to 7800 and speed to about 66 MPH, I thought this was due to higher air and water temps and maybe the need for new plugs.

    A month ago I did some work on my ski and have this set up:

    RIVA Stage II Kit
    RIVA Heavy-duty Supercharger Clutch Washers
    RIVA RXT Thermostat Kit (158 degree)
    RIVA Pro-Series Reduction Nozzle
    RIVA RXT Pro-Series O.P.A.S. Block-off Kit
    SS Wear Ring

    Dropped ski in water weekend before last and only had 7800 RPM and 68.3 MPH.... Spent all week looking for the obvious; boost leak (none found), oil level, fouled plugs, mis-aligned pump seal... all checked out.

    Dropped ski in water this past weekend and had a hard time reaching 7800 RPM and speed dropped about a half MPH versus week before. I just ordered a SC rebuild kit, this seems like the next logical step....

    I just dropped $3800 in parts and labor to upgrade my ski to Stage II + and now another $325 for the rebuild kit... I hate chasing this with cash.

    UPDATE: Had the SC rebuilt today, RPM's were actually down... couldnt get above 7680... speed was 67.3. Everytime I put it in the water it seems to get a bit worse. I need some help.

  2. #2
    moultrie rxp's Avatar
    Join Date
    Jul 2006
    South Carolina


    You will really be surprised how the humidity and temp affect your RPM's. In 2 weeks time I lost 150 to 200 RPM's because of the temp and humidity. Temp went from the low 80's to 100 in 2 weeks and my RPM's dropped. I am using the 84 ring in my nozzell to keep my RPM's up now but when the temp cools off in the fall I can go back to the 82 and still hold my RPM's.

  3. #3
    PEST!'s Avatar
    Join Date
    Jun 2008
    Rockledge Florida
    If I remeber corectly the impeller is changed in a level 2 you might need to tweek it. I am no fan of "KITS" not everything in the kit fits the way you ride.

  4. #4
    Richieb's Avatar
    Join Date
    Oct 2008
    Sydney, Australia.
    So true.

    It is not only about bolting it on, its how you make it work with the rest of the ski.... and how you ride.

    There are many hrs of "Tweeking" here and there, before the final product can be rolled out as finished.

    If the RPM stays the same, but more work has been done, then the un-sung hero.. Torque, which is what forces the water through, may be greater, but the prop will stop at peak for that setting... so step up a pitch or two, and see if it pulls the water harder.

    A few months ago I watched a bloke getting all cranky with his P-X having put all he could onto the ski, and just got to a GPS 68mph.

    The theory was if he upgraded this and that, it would defo hit this speed... it didn't. What he missed was the fine tuning of it all.

    Spend more time on R&D than you need to, it will pay off in the end.

    Ambient conditions are a real big factor in obtaining the RPM.
    Last edited by Richieb; 06-26-2009 at 07:20 AM. Reason: mis-triped

  5. #5



    If you've been following this thread you basically can see the problems I have been having, or thought I was having.

    Back to the beginning....

    Last year i was running 8060 rpm in salt water on the east coast, speed was 70.5 on GPS with a stage I kit.

    Dropped ski in fresh water in mid-west (kansas) end of last summer rpm was 7800, speed 67 - 68. Thought it was time to change S/C clutch washers, oil, plugs etc.

    Dropped in the stage II kit plus thermostat, SS wear ring and pro series block off. Dropped ski in the same mid-west Kansas lake a month ago, rpm was 7600 - 7700, speed 67.

    During the last month I have been going nuts checking and double checking everything looking for the reason I cannot get to the rpm/speeed listed for the stage II kit.... no luck. Spent an additional $500 on parts/labor for a supercharger rebuild thinking this was the problem.... after rebuild, no change. Total frustration at this point.

    Sorry for the history, but it's relevant and maybe helpful to some of you.

    It's 4th of July weekend and I'm taking the ski back to the east coast for my annual race week. At this point I'm sure the ski is not running up to par.... and im going to get my ass kicked by the x boats this year.

    Drop in water today (salt water, same as place last year) and absolutley take off like a rocket... acceleration is un - freakin real, rpm 8060 and speed (on garmin GPS) is 73 MPH! Holy crap..... I kid you not, I pounded the crap out of an rxt-X.

    The only things I can see that are a difference between mid-west and here are: salt water versus fresh and elevation.... elevation is Kansas 1350 feet, elevation here 0.

    I would have never guessed..

    Any comments on this phenomenon? I am truly shocked at the difference in this ski and the performance...
    Last edited by Meteor; 07-05-2009 at 08:05 PM.

  6. #6
    finalcut's Avatar
    Join Date
    Jun 2009
    toronto.. ontario

    Question need help

    07 rxt with 26hrs on only getting 6480 rpm's...what could it be...ajust throttle? please.....

  7. #7
    Banned User
    Join Date
    Aug 2007
    Reading PA
    check supercharger sounds like u might have dropped a washer...

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