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    Site Admin Green Hulk's Avatar
    Join Date
    Apr 2005
    Morgan City, LA

    New members wanting to modify your skis. *Please Read*

    We were all new once and have questions, but 99% of the time your questions have been asked dozens of times.

    Before creating a new thread, do a search to see if its been asked before and contribute to that thread rather then creating a new one.

    If you don't know where to get parts, click ONLINE STORE in the links section on the left side bar. Using the coupon code: greenhulk when checking out will save you 10% off of RIVA, R&D and Solas impellers.

    If you are interested in modifying your ski for more performance and better handling this article will serve to inform you of whats available and hopefully guide you in the direction you want to take in modifying your ski.

    Let's start with the basics.

    The very first thing you should do to your supercharged watercraft if you have an 07 or older ski is switch the stock ceramic supercharger clutch washers for the special RIVA metal washers that are now on the market. A failure of a ceramic clutch washer can cause many problems and will destroy your oil pumps. If the oil pumps are not checked/replaced after a ceramic washer failure you run high risk of serious engine damage in the future.

    A few of the very first things most people do to their skis is install an intake grate, remove the OPAS system (training wheels) and install a Riva finger throttle/wider handlebar kit.

    As far as grates go the Riva grate has been proven time and time again to out perform all others and even increases speeds on the higher modified crafts. If you are a rough water rider then the R&D Aquavein intake grate has proven to be the best as it gives better than stock hook up.

    When removing OPAS you have several options. On the GTX or RXT platforms the OPAS paddles move up and down. Many times a filter in the system can become clogged causing the OPAS paddles to remain in the lower position below the waterline resulting in poor performance. You have the option of purchasing a Riva Competition OPAS kit which basically snaps in place to hold the OPAS paddles in their upright position at all times, or just remove them completely. Riva makes a block off kit for all of the Sea Doo 4-Tec's that completely removes the OPAS system. This is the route most choose to go. For the RXP, Riva makes a Pro Series block off kit that actually extends the OPAS opening further rearward which improves handling tremendously over the standard block off plates. These Pro Series block offs are IJSBA legal for racing. For those that aren't concerned with being race legal you have the option of going with the Race Engineering OPAS block off kit which extends the hull to cover the entire OPAS opening. Handling with these block off's is superior to all others. They improve hookup in chop, cornering and the overall feel of the ski is amazing.

    First i will discuss staged kits and then i will talk about mixing and matching components.

    Many people choose to jump straight to a Stage 1 kit which includes all the basics. Riva offers a Stage 1 kit that includes an intake grate, a 14/19 Solas impeller, 3" air intake kit, and a 2 degree pump wedge.
    The 14/19 impeller will deliver better acceleration and top speed. The air intake will help the engine make more power which is necessary to turn the high pitch impeller at top RPM's. The wedge helps raise the bow of the ski up which also increases top speed. Some people don't like the way the wedge makes their ski handle while others love it. For RXP owners, they may opt to go with the VTS extension rod which greatly improves hole shot when running a wedge.

    If it's more power you seek then it's available in many forms. Basically, the addition of an external intercooler, Riva/Vortech supercharger impeller, thru hull exhaust and Solas 15/20 impeller will bring you to Stage 2 status. Riva's stage 2 kit offers all of the components of the Stage 1 kit plus the parts i just mentioned above and also includes Riva sponsons. Sponsons work to improve the handling of your ski and improve straigtline tracking thru chop.

    The 15/20 impeller is necessary at the Stage 2 level of modifications because you are obviously making more power now and with a smaller impeller you would find that your engine ran against the rev limiter. For optimum performance you want your pitch to hold your RPM's just under the rev limiter so you effectively use up all of the engines usefull powerband.

    The intercooler in the Stage 2 kit is an external intercooler and makes a ton more power than that of the stock intercooler which is mounted in the intake manifold. The stock intercooler is removed and then blocked off with a billet block off plug that is provided in the kit. It's also worth mentioning that the stock intercooler is extremely restrictive. My testing has shown a 1 psi increase in boost when going to the external intercooler.

    To make room for the Riva intercooler a thru hull exhaust must be used. The thru hull exhaust not only gives better performance by being less restrictive and it sounds amazing.

    Another exhaust option is the shorty water box. This water box is shorter than stock which enables you to easily remove the supercharger without having to move the exhaust back out of the way. It's also free flowing and increases performance. This water box fits the Riva thru hull exhaust location for those that already have the Riva thru hull exhaust kit. If you don't already have a thru hull exhaust all you need to buy is the exhaust tip, a coupler and of course the shorty water box.

    For those not wanting to go with a thru hull exhaust, but still want to run an external intercooler an option would be to go with the Rotax Racing intercooler with their intercooler plumbing/mount bracket kit. Both are good intercoolers, but i have tested them back to back and the Riva has shown to have a slight edge over the Rotax Racing unit.

    I have been asked many times, "why not leave the stock intercooler in place while running the external intercooler? Two has got to be better than one right?" The answer is no! Intercoolers are restrictive devices. If you throw both of them into the mix performance is deteriorated.

    The Riva/Vortech supercharger impeller provides more boost than the stock supercharger impeller, but more importantly it delivers a greater volume of air. This impeller noticeably increases acceleration. In fact, many people with a basic Stage 1 kit have used this impeller and were very excited with the improvement it gave them.

    If you find you want more performance than what a Stage 2 can deliver there is always more available To bring your ski up to a level of Stage 3 you can add an aftermarket ECU. Riva offers a Stage 3 kit which consists of all the components in their Stage 2 kit plus an ECU, 50# injectors, higher boost supercharger with modified front housing, higher rate valve springs with lightweight titanium retainers, 158 degree thermostat, 15/19 3 blade Skat impeller and a adjustable venturi nozzle.

    There are a couple of aftermarket ECU's available to us. The Riva ECU and the Rotax Racing ECU. The important thing to remember is the Riva ECU is mapped to work with 50# injectors. (stock injectors are 38#) The Rotax Racing ECU can be run with the stock injectors, or larger 42# injectors if running a higher boost supercharger. (more on this later)
    Both the Riva and Rotax Racing ECU's have a higher rev limit of 8650 RPM's. With either ECU you must upgrade your valvetrain to handle the higher RPM's to prevent valve float. The valvetrain upgrade Riva offers in their Stage 3 kit consists of higher rate springs, a shim that goes under the spring and also lightweight titanium valve spring retainers. This valvetrain kit is effective and easy to install without removing the head using Riva's valvetrain tool. Rotax Racing offers lightweight aluminum valve spring retainers and spring shims, but it is advised that if you plan on running 8500+ RPM's with the Rotax Racing retainers/shims that you also have the valves lightened. This requires head removal. It is also advised by Rotax Racing that the aluminum retainers be inspected and replaced if necessary after every 25 hours of use.

    There are also a couple of 158 degree thermostats on the market. Rotax Racing offers a complete thermostat that just bolts in place. Riva offers a kit that you use to modify your stock thermostat to convert it over to 158 degrees. The stock thermostat is a 188 degree unit. Your engine running 30 degrees cooler with the aftermarket thermostats also keeps the oil temperature down which prevents oil viscosity breakdown and extends your oil life. The aftermarket thermostats help reduce heat fade in the hot summer months and enable you to run your max RPM's.

    The adjustable venturi nozzle offered in Rivas Stage 3 kit is actually something can be run on any ski with any level of modifications. This is a handy tool to have so that you can easily dial in your RPM's for maximum performance without having to repitch the impeller. It comes with 3 ring sizes. The larger the ring the higher the RPM's. The smaller the ring the less RPM's you will turn. Also, most people find that the 81mm ring gives them the highest top speed. The stock venturi is 83mm.

    The supercharger impeller that comes with the Riva Stage 3 kit also comes with a modified front housing that accomodates the taller blades on the impeller. This supercharger produces a great deal of boost and also moves a very large volume of air resulting in greatly improved performance.

    This supercharger isn't limited to just skis with a Stage 3 level of modifications though. I have seen people with as little as a Stage 1 kit run it with great success. If you aren't running the Riva ECU and you want to run this supercharger you must use 42# injectors with either the stock or Rotax Racing ECU's.

    There are quite a few options when it comes to superchargers. I will list below the different superchargers on the market and which injectors will be necessary to run them. The list will go from the weakest supercharger to the strongest.

    Stock SC - stock injectors

    Riva GenII - (same as Green Charger impeller)

    Rotax Racing High Boost - stock injectors with stock intercooler. 42# injectors with external intercooler OR stock injectors with a Rude rising rate fuel pressure regulator.

    Green Charger - stock injectors with stock intercooler. 42# injectors with external intercooler OR stock injectors with a Rude rising rate fuel pressure regulator.

    Riva Stage 3 SC (pro series) - With Riva ECU you will need the 50# injectors because that's what it's mapped for. With stock ECU or Rotax Racing ECU you will need 42# injectors OR stock injectors with a Rude rising rate fuel pressure regulator.

    Sea Doo OEM X model supercharger
    - With Riva ECU you will need the 50# injectors because that's what it's mapped for. With stock ECU or 07 and older Rotax Racing ECU you will need a Rude rising rate fuel pressure regulator.

    Rude Performance "Rude Charger" or Les Cooke "B" kit SC - With Riva ECU you will need the 50# injectors because that's what it's mapped for. With stock ECU or 07 and older Rotax Racing ECU you will need a Rude rising rate fuel pressure regulator.

    When running these higher boost superchargers its important to feed the supercharger as much air as possible. Those that have an RXP are lucky in that Riva now has a 4" rear air intake kit that works extremely well. Many people have fabricated their own custom 4" intakes using the R&D 4" adapter coupler that attaches to the SC opening and utilizes a 4" flexible hose that runs to the front of the ski. While this setup is good, it's not as good as the Riva rear air intake. I have found 1 psi more boost from switching from the 4" front intake to the Riva rear air intake.

    I think i have covered the basics. This forum is an encyclopedia of information. Doing a search for almost any topic will bring up pages and pages of information for you to read and learn from.

    Here is some good info provided by forum member Vern
    Quote Originally Posted by Vern
    Jerry covered so much in his first post, but I thought I would add my take on CHEAP Stage 1 & 2 'recipes' for people who want to spend the least amount of $$ for additional speed.

    FIRST, GET METAL WASHERS INTO YOUR SUPERCHARGER!!! As Jerry said already ... but it is critical and should always be the FIRST thing you do to avoid pain and heartache and downtime.

    Cheap ‘Stage 1’
    Best 4” rear air intake you can find/make ($100 or more)
    Riva intake grate $130
    Fill ride plate holes
    Riva or Skat adjustable venturi, 81 mm ring ($345)
    2 degree Riva wedge $110
    Stock prop, remove impeller cone, tweak trailing edge to get rpms at 8100
    The stock prop actually works OK until you go to a Stage 2. If you have the money, a Solas 14/19 4 blade is a good choice for a Stage 1 too.
    The above setup should get most people to 73 mph, up to possibly high 74s, and is dirt cheap.
    Depending on how fast you are going, you may get porpoising and need the RE blockoffs ($310).

    Cheap Stage 2 (add to Stage 1 above)
    Add a good intercooler and metal intercooler tubing $400 - 1500
    Add 15/20 4 blade ($275), try it stock, maybe tweak trailing edge later if rpms are under 8000
    RE blockoffs ($310) - you will need them at the speeds you are going now
    Should be 75++ mph

    Stage 2+
    Add a good supercharger impeller – many choices, best bang for the buck seems to be the Riva S3, there is also the RR high boost or A kit from Les Cooke, and Jerry's Green wheel, all are good. Roughly $500 - $750
    To be safe, should add 42 lb injectors with the higher boost SC impeller. $250
    You could also now likely switch to the new 15/19 3 blade impeller, possibly with a tweak to the trailing edge. $340
    Should run 76+ mph, some may hit 78+ with this setup.

    Adjustable Nozzle
    Its been mentioned before, but getting an adjustable venturi nozzle (Riva one sold on this site is good) and putting in the 81 mm ring, then tweaking the trailing edge of your impeller to get your rpms to 8100+ will add speed whether you run a Stage 1 or 2 RXP.

    Altho there are tons of variables involved with our skis impellers, pumps, etc, there is a distinct relationship between a skis intake cavity size and optimal exit nozzle size. Since most of us have not messed with modifying our intake tunnel (yet), trust us when we tell you that most of our skis like an 81mm exit nozzle (Stage 3 might like 82 mm, I can't personally speak to that one). Put it on, tweak your impeller trailing edge, you will gain speed.

    IF anybody messes with reducing the intake cavity somehow, I would be willing to bet that they will have to change (reduce) the size of their exit nozzle to get the maximum speed out of their new setup.

    If you read much about the development of variable intakes and exits (unfortunately only in use on larger boats), it quickly becomes clear that only when they were reduced in sync did it generate better results. Just FYI.

    If you have questions on any modifications to your ski use the search featur of this site or make a new post. You will find that this site is a wealth of information.
    Last edited by Green Hulk; 03-31-2008 at 06:39 PM.

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