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  1. #31

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    Quote Originally Posted by outnumbered View Post
    Is that question for the OP?
    sorry.....super jim what intake grate are you running? ride plate mod?
    Harry

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  3. #32

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    Quote Originally Posted by yellow jacket View Post
    u haft to haft the power to turn a taller prop if he would put a et 20lb wheel in then he might turn 9200 with the 13/20...
    I have been trying to get this point across for a long time. This is one of the reasons, I run the 20psi wheel and bigger cams on my heavy FX cruiser. I was bending "taller" props last year and fighting cavitation but my speed was slowing increasing. I went from 91.5 to 93 then 94. I did not get a lot of testing time last year, because I had to move my MIL (massive hoarder situation) and it cost me my prop.

    When I went to pull the ski out of the waster, no crank, good battery, the stock liner swelled around the prop. I tried to cut it off and save the prop, but my brother cut into the prop. Over the winter, I stole the pump/prop out of my other big bore ski (which needs lots of attention) and bent it to match. I added some more cam overlap and was tuning with Jesus over the winter. Big sweeps in LSA are hard to get to idle, so I have to go in 2 degree increments to get there. Then when I am out on the water I can send JesusG data logs as needed.

    3 years later and a total of 20 hours on a 2016 FX Cruiser SVHO my ski went 95 mph with 2 bars down from a full tank and a 160 pound rider on one year old 93 octane pump gas and Royal Purple octane boost. The tune up needs work. The idle needs to be increased and it is too rich mid range.

    I am impressed with pump wedge it really gets the ski up and on the ride plate. It is like driving an automatic race car with a high stall converter.

    I am certain you can go just as fast with smaller wheels and cams, but you will have to turn significantly more rpm and use a shorter prop.

    I like the massive bottom end and raw power romping around in the bay, so this is where I went with my combo.

    Robert

  4. #33
    Super Jim's Avatar
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    Quote Originally Posted by xtturbox View Post
    sorry.....super jim what intake grate are you running? ride plate mod?
    Harry
    I have the Riva intake grate that came with the stage 3 kit.

    I also have the luck13 cone with no spacers with the siphon tube removed and sealed. That was a plus.

    * I am also now using the new Macsboost intake airfilter. I gained about 110 rpm by replacing the Riva power intake with Mac's new filter. Bolts directly on the supercharger and has a nice large internal velocity stack. A pro racer on a stock class FXSVHO said he gained 200 rpm doing the same thing.

    I am using my factory ride plate that I modified; Similar to Jim's cut ride plates. Maybe not as good as Jim's So I have one of Jim's Performance plates on the way. I might even pick up a little more speed next week.
    Last edited by Super Jim; 05-31-2019 at 11:55 AM.

  5. #34
    Super Jim's Avatar
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    Quote Originally Posted by xtturbox View Post
    I'm still confused why the motor won't pull higher rpm's with the different prop. The motor is what creates the rpm isn't it? I understand the prop is like car gearing but why won't the 13/20 he used rev higher???

    it's kinda like 4.10's vs 3.73 but with both my car will still redline 7500 rpm's
    4.10's get there faster and 3.73 have a higher top end but both will hit redline
    One important thing to consider is, a direct drive supercharged PWC engine will respond much differently to rpm than a normally aspirated or even turbo charge PWC engine. On a naturally aspirated pwc, you can gain speed by going to a steeper impeller as long as you have enough hp to keep pulling the rpm to the same peal level but you loose some low end. Just like the car rear end gear ratio example. If you reduce the pitch you loose top speed but gain acceleration. But with a direct drive supercharged engine, as you increase rpm you increase boost and therefore more hp. So by decreasing pitch you gain hp and therefore top speed to a point while also gaining acceleration.

    Sure, you can just go with a lager supercharger wheel and get more boost at lower rpm or also increase rpm and get even more hp. But there is always a trade off. Many people like the all around performance of the 17 lb wheel vs the more top end power of the 20 lb wheel.

    As for strain on the engine, extra rpm and/or extra boost will increase strain on the engine. The safest bet is to leave it stock but I just can't do that with anything. With the Riva valve retainers, the valve train seems to be reliable in the 9200 rpm range and maybe a little beyond.

  6. #35
    Super Jim's Avatar
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    Quote Originally Posted by yellow jacket View Post
    u haft to haft the power to turn a taller prop if he would put a et 20lb wheel in then he might turn 9200 with the 13/20...
    I have no doubt a 20 lb wheel would probably pull the 13/20 to 9200 so I would have even a higher top speed. Who knows, maybe someday I will have to do it. For now I want to be just a little conservative.

  7. #36

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    impeller

    Quote Originally Posted by Super Jim View Post
    I have no doubt a 20 lb wheel would probably pull the 13/20 to 9200 so I would have even a higher top speed. Who knows, maybe someday I will have to do it. For now I want to be just a little conservative.
    It's good to know...I have mine apart currently and looking at which prop to use.
    thx Harry

  8. #37
    95.4mph FZR FZeeR's Avatar
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    Quote Originally Posted by rcrisafulli View Post
    I have been trying to get this point across for a long time. This is one of the reasons, I run the 20psi wheel and bigger cams on my heavy FX cruiser. I was bending "taller" props last year and fighting cavitation but my speed was slowing increasing. I went from 91.5 to 93 then 94. I did not get a lot of testing time last year, because I had to move my MIL (massive hoarder situation) and it cost me my prop.

    When I went to pull the ski out of the waster, no crank, good battery, the stock liner swelled around the prop. I tried to cut it off and save the prop, but my brother cut into the prop. Over the winter, I stole the pump/prop out of my other big bore ski (which needs lots of attention) and bent it to match. I added some more cam overlap and was tuning with Jesus over the winter. Big sweeps in LSA are hard to get to idle, so I have to go in 2 degree increments to get there. Then when I am out on the water I can send JesusG data logs as needed.

    3 years later and a total of 20 hours on a 2016 FX Cruiser SVHO my ski went 95 mph with 2 bars down from a full tank and a 160 pound rider on one year old 93 octane pump gas and Royal Purple octane boost. The tune up needs work. The idle needs to be increased and it is too rich mid range.

    I am impressed with pump wedge it really gets the ski up and on the ride plate. It is like driving an automatic race car with a high stall converter.

    I am certain you can go just as fast with smaller wheels and cams, but you will have to turn significantly more rpm and use a shorter prop.

    I like the massive bottom end and raw power romping around in the bay, so this is where I went with my combo.

    Robert
    So you’re saying your FX Cruiser does/did 95mph on the ET 20 wheel? Please share details here that’s pretty impressive...What cams? What rpm did you hit 95mph? Etc??.

  9. #38

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    Thanks. My build is in the build thread. I can post some more details later tonight. It has taken 3 years and lots of parts swapping and tuning to get it there. I run RC-2 cams in this motor.

    Robert

  10. #39
    Lake Lion
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    Details? We want video!!!


  11. #40

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    Ok. This is from memory, so I will try and be as accurate as possible.

    The initial build was the standard Riva Stage 3 kit with a 20 pound wheel, stock fuel pump, 13/20, Riva water box stock location exit, Jims cut plate. Map tuner no data logger. I had a AFR gauge in the mirror and a non functioning TTO tach (pos). The original tune was the Stage 3 9500 AGR. The fuel is Exxon 93 with various octane boost. Which ever was available. The last 2 bottles I have are Royal Purple. I would mix the octane boost as directed for extra protection. I asked for safe pump gas tune ups from Jesus.

    This went 91.5 mph in July in the heat with my nephew riding 150 pound rider full tank of gas. I could go 90 mph and I am 200 pounds. This was the first speeds runs on the ski. I was hooked after that. What an impressive machine and the after market parts just as impressive and free tune ups. The ski had 9 hours on it. We used iphone gps app and garmin gps for speed runs. The results were always within a tenth of each other. The phone and garmin were always in the water tight compartment.

    Over the winter I had the stock cams reground. I actually have two identical 2016 FX Cruisers in white. I sent both sets out and one ground for RC-2 and the other RC-3. I installed the RC-2 cams with very little overlap, adjustable gears and shimmed them. Fresh oil and plugs for the summer. The map data logger and map edit came out late and I installed that also. I decided to build my other ski up to and went over board with a big bore kit. This took longer, so I had two 13/20 pumps that I interchanged over the summer. This is when I bent my first impeller. I got that plastic gauge, but just used a metal rule and made a template for reference to make sure each fin was bent the same. Part way through the summer I stole the deans clutch from my big bore ski because I was worried the stock would go out and possibly hurt the motor.

    I was bending taller props and trying to go fast with the minimum rpm possible. I figured the ski could live a long time under 9000 rpm. I am not an expert on max rpm, but mine only live at high rpm for short periods like a few seconds at a time.

    I would use map edit to set the limiter down under 9000 rpm and make a pull. Not knowing where the boost was going with the new cams. The boost was higher then I though it would be. Logging the data was great. I was reward with cavitation and the ski bouncing off the limiter upon taking off. After adjusting the trim and riding style and taking some of the AGR out of the tune from take off. The ski would launch.

    Each prop I bent was a little taller. The ski would go 92 with me on it and it hit 94 once with my lighter rider rpm were 9330. We wore a helmet this summer. Recording data was a pain in the ass, because you had to turn off the ski, plug the box in and switch the dash connector all leaning over the front of the ski. Both myself and my nephew like riding with a dash. This is still sucks today.

    At the end of the season, I was rewarded with a swollen liner and no start ski. The impeller got cut while trying to cut the liner off. I bent the other impeller to match and scrapped it.

    Over the winter I installed: deans transom plate mod, RD liner, adjustable cam tensioner, pump wedge, stronger cam buckets, reshimmed cams and tried numerous overlap settings. I would have to get idle tune ups from Jesus and make my own. This was a major pain in the ass and time consuming. Small cam overlap changes were all I could make to stay in the tune up window.

    Currently, the ski will not idle in the water under load. I need to get some data to Jesus. The mid range is fat around 3000. This is typical as the overlap pollutes the intake charge. This needs to be addressed. However, upper rpm is a monster and it went an honest 95 with the limiter set at 9300 for the first time. The ski tune up needs work and this will take some riding and tuning. I think the wedge freed up some drag and the latest impeller is the tallest one to date.

    Sorry for the long post.

    Robert

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