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  1. #1
    Vern's Avatar
    Join Date
    May 2005
    Grand Haven, MI

    My RXP update - Summer '08

    I have not been as active this summer with RXP testing and posting, so I thought I would post an update, just FYI of where I am at this summer. Work got in the way, had a LOT of travel, was out of town a lot and that really killed my test/tune time. I also bought a boat and that distracted me a bit too. A bit long (sorry!) and no amazing breakthroughs, but just wanted to keep my GH friends in the loop a bit ...

    Summer 2008
    Switched to Riva ECU and Valvesprings over the winter. Also pulled the motor and gas tank and updated the flywheel bolts, cut out the ‘feet’ of the inner tub under the gas tank, and laid in 7 layers of carbon fiber and epoxy resin to eliminate pounding/stress cracks. Modded a Riva grate, reinforced the pump tunnel with CF and resin, added the R&D girdle kit. Added the GH shorty waterbox, still was running an A kit SC (drop-in wheel like the Green Wheel). Installed an XS intercooler to replace my clogged Riva IC. Aligned the motor, added a new carbon ring setup, threw it in the water.

    I was fighting boost leaks for awhile … initially I was running a pitched up 15/20 4 blade (Carl trued up the leading edge and added 1+ degree on trailing edge, so more like a 15/21+) and 81 mm nozzle. First time out ran 7900 rpms … switched to a trued and pitched up 15/19R (I had Carl bump this one up 1.5 degrees) 3 blade and 83mm nozzle, tightened up clamps, ran 8200 - 8300 rpms. GPS has been very flakey and shuts off … no speed numbers. (I had initially planned to run the X charger, so that is why I had Island Racing pitch up both my props).

    RPMs fell back to 8150 next time out … got pissed, ordered another XS IC, brass fittings, and drilled and tapped for a ¼ inch bleed line off the top of the front tank too. Ordered two 2.75” hump couplers and new Riva rear filter element as well. Installed all that and ran solid 8300 rpms all day, again no speed, GPS quits every time I hit a wave.

    Over the winter my VTS motor had crapped out … so all my testing this year was with VTS in ‘standard’ position … not sure if that robs rpms, but it does rob speed. I recently threaded and plugged my X charger oiling hole and added Riva metal washers (and 2 shims so slip is now 110 in/lbs) and this weekend I hope to have the time to put a new VTS motor in and try out the X charger.

    Installed the X charger this past weekend, gained 100 rpms, went from 8300 with the A kit to 8400 rpms. Ski ran great all weekend, still no numbers, GPS is toast. Boost gauge is no good either … was reading 8 lbs boost at 8400 rpms, but no way is that accurate due to the way the ski is running. 8400 rpms with a pitched up 15/19R (plus 1.5 degrees on trailing) and 83mm nozzle is OK, especially since testing indicates that my intake grate mods resulted in cleaner/more water to the pump, but a loss of 100 rpms (I need a little less pitch to correct for that).

    Ski sounds really good with the X charger, rear air intake and GH waterbox. Got a lot of compliments on how fast it is and how it sounds. A friend of mine rode it and he was amazed at how fast it was and how the pull just never ends.

    I like hump hose couplers, they seem more forgiving and easier to seal than standard silicone couplers.

    There is less oil in my catch can despite more rpms and boost than last year – others have noticed the same thing and usually attribute it to the Riva Valvesprings.

    Modifying the Riva grate (I sharpened the trailing edges, rounded the leading edges and worked the wing a bit) seems a waste of time, the pump is likely getting too much water already. Based on tests that Dan (RXP'n in MI) did with similar mods, my intake grate mods equal a 100 rpm loss.

    A GOOD boost gauge is a good investment – guys who are not getting optimal performance and don’t have a boost gauge often have undetected boost leaks.

    The GH box makes swapping SCs a very quick job.

    I get water in my VTS motors (I tore one apart and lots of water in it) that kills the motors every year basically – anyone know why/how to stop that?

    I got way behind in my testing this year due to a lot of unforeseen travel and other time-robbers. So this year I also learned to ‘let it go’ at times, and when I DID manage to get to the cottage and have time to ride, I just rode … so the ski has been very reliable this year again (170+ hours on it now). If I had time, I would do some prop tweaking and swapping (and grate swapping) to get my rpms to 8500, but it is so nice just to get on it and go, plus it is very fast as is. 80+ mph is not everything … I have still had a lot of fun this summer even tho I am not sure if I have hit 80 mph yet.

    Also on the plus side, my Glastron Carlson jetboat is running great (60+ mph GPS) and throws a huge rooster tail and is a very fun alternative to my RXP.

  2. #2
    REID2168's Avatar
    Join Date
    Jun 2007
    My House
    im sure youll get where u want Vern ........ sounds like what u have so far is working good for u!

  3. #3
    AKA: Larry lafjax's Avatar
    Join Date
    Jul 2006
    Jacksonville, Fl
    Good report Vern...sounds like you are making it work and enjoying riding!! Riding is important...I get wrenching fever every once in a while but would rather be riding a dependable ski and taking it easy.

  4. #4
    outboard john's Avatar
    Join Date
    Jun 2006
    Escondido, Ca.
    Vern, would like to see pics of your boat.

    Thanks OBJ

  5. #5
    Vern's Avatar
    Join Date
    May 2005
    Grand Haven, MI
    Thanks guys. John, the ski looks pretty stock ... which is how I like it. But its not a sleeper unfortunately, it sounds too good and is too well known on my home waters, so I only get to race boats lately. The only part that looks unusual about it is the CF layers inside under the gas tank ... but those are not easy to see now. I do have pictures of that process already posted on here somewhere if want to see those ...

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