550/800 conversions stock pump
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  1. #1
    PWCToday Newbie
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    550/800 conversions stock pump

    I am in the middle of a 92 550 sx/800 swap.I see guys that have done this swap going to 750 pumps. Is this mod a must. What are the gains with this mod?I apologize if this is a stupid question.

  2. #2
    PWCToday.com Is My Home Away From Home theVetteman3's Avatar
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    Re: 550/800 conversions stock pump

    Nope not at all a stupid question. Is this a stock / limited 800 or ported? I ran a 550sx pump in my ski for a long time, and didnt' put in a ported 800 because I was worried about the impeller.

    Basically with the stock pump many guys have run a 20 pitch with a dual carb 750. With things set up right that's a low 50s ski. Because of the mixed flow pump, it has been my experience that there is one ideal pitch for your power output. If you go down trying for more low end, it wont work and you'll just massively cavitate. Impros said they could pitch up to a 21 but I didn't want to spend time and money seeing if that was right for my 800, or if I'd need to have it re-pitched even taller. In theory this can be done, but now at this point many have gone the pump swap route.

    The 750 pump gives you a much broader range of impeller choices. And because this is so much more thrust than the ski has with the small pump, it is very hard to get the ski to cavitate. It feels more like gently slipping the clutch or traction control easing your acceleration, if anything. Very easy to modulate the power. The trick is, there are many ok choices, perhaps one which is equal to the ideal 550 pump equivalent, and then a few choices which are better. There is definitely some overlap.

    I found that with my limited 750, a Skat 13/18 small hub swirl was about equal in performance to the 20 pitch I had in the 550sx pump. A Skat 13/18 C75 big hub swirl had significantly more low end. And my favorite choice was a 10/16 hooker. That gave the most low end and still allowed the engine and pump to rev out to 55+ mph.

    The pump swap is definitely worth it. If you check my 550/750 pretty red / angry cardinal build thread in the individual builds section, I have tons of detail on this. The one thing you can notice, is that initially with the 13/18 small hub swirl, I was slow to claim much of a performance advantage. This is because there wasn't much. When I went to the 10/16, that's when you can tell things really improved.

    Basically if done well the 750 swap is absolutely superior. And it gets you away from really expensive high pitch 750 impellers. There is more low end, more high end, and just a better performance envelope all over. If you stick with the 550 pump, I would talk to Dave at Impros and see what he recommends. Depending on your set up, you'll probably be at a 20 or 21 pitch impeller.


    Here's the build thread, right where I rode the ski for the first time with the 750 pump:

    http://www.pwctoday.com/showthread.php?t=339768&page=37
    1985 JS550/800 "Pretty Red": Newmiller 800, Rhaas 750 pump conv. [56.3mph gps]
    2009 1100 SJ:
    Kawi 1100 build in progress
    2009 SJ MINT:
    KP steering adaptor, Worx 228 intake [45.8mph gps]
    1987 WJ650:
    6M6, JD Intake Grate, 17/20, cheater pipe [47.8mph gps]
    1994 XiR: 830cc Superstock, PJS side draft, 13/18 swirl [53.7mph gps]
    1998 SXI PRO:
    3DR hull mods [TBD]



  3. #3
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    Re: 550/800 conversions stock pump

    Thanks for the info

  4. #4
    PWCToday.com Is My Home Away From Home john zigler's Avatar
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    Re: 550/800 conversions stock pump

    I too have done many conversions.

    Back in the mid 90's I had a dual carb 750, 210psi, ported 750 in a 550. Custom SKAT impeller. Ski ran 54 mph on GPS, and pulled OK. This exact engine was an arm ripper in a 750 hull....

    We have now have been building conversions with the 750 pumps in the 550, and IMO is WAY better. 750 pump is much more efficient, and as stated above impeller choices are more plentiful. It is just to easy to overpower a 550 pump. IMO if yo do a stock 650 conversion, it is still OK, but anything more is too much for it. I like a good low end snap.

    I did do a stock SXR 800 in a 550sx, with 750 pump. 52mph and crazy acceleration. (Much better than any 550 pump). The ski would literally want to leap out from under you.

    Price to do a 750 pump conversion is much more though. I also run cut back Skat impellers, with TBM Pump stuffers. Last build for a customers ski was over 5k.


    I would build according to your budget, and overall goals.
    RCJS also doing business as WATCON
    608-743-1305 9am to 5pm CST m-f
    email watcon@watcon.com

    Please visit our web sites

    new parts / products / services www.watcon.com
    used parts www.rockcountyjetski.webs.com
    thank you

    Please check out and like WATCON on Facebook

  5. #5
    PWCToday.com Is My Home Away From Home theVetteman3's Avatar
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    Re: 550/800 conversions stock pump

    That's some good info there John. What impeller and pipe did you use on your 800 build?

    On my Newmiller ported freestyle 800, I am surprised at the ease it hit 56.3. The impeller choice was clearly under propped, because I gained low end when I went from a 80mm nozzle to 76 with my 11/17 hooker. That power band was good but it still didn't grab well enough down low. BLRider and I are beginning to see that for higher hp built engines, they need an impeller with more "grab" down low. Meaning a regular C75 and not a hooker. When I have my ski rebuilt in my new hull, I'm going to start with a 15/20 C75 swirl. I think I might try a cut back impeller and TBM stuffer too.

    The 10/16 hooker and 80mm nozzle I found to be an excellent combination for my limited 750, lime green head small pin with the PJS pipe. For the money invested it was just a very nice package. The 800 had real strong mid range but I need more bottom end bite. I think you really need to match the hooker impeller to the engine hp well or you wont have enough grab.

    Regardless, with the 750 pump speed comes super easily. Depending on your set up it can be much harder to get it to break 50 with a 550 pump.
    Last edited by theVetteman3; 07-03-2019 at 07:50 AM.
    1985 JS550/800 "Pretty Red": Newmiller 800, Rhaas 750 pump conv. [56.3mph gps]
    2009 1100 SJ:
    Kawi 1100 build in progress
    2009 SJ MINT:
    KP steering adaptor, Worx 228 intake [45.8mph gps]
    1987 WJ650:
    6M6, JD Intake Grate, 17/20, cheater pipe [47.8mph gps]
    1994 XiR: 830cc Superstock, PJS side draft, 13/18 swirl [53.7mph gps]
    1998 SXI PRO:
    3DR hull mods [TBD]



  6. #6
    PWCToday.com Is My Home Away From Home theVetteman3's Avatar
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    Re: 550/800 conversions stock pump

    Quote Originally Posted by theVetteman3 View Post

    Basically if done well the 750 swap is absolutely superior. And it gets you away from really expensive high pitch 750 impellers.
    Should be obvious but I meant expensive 550 impellers, not 750. A good swirl 750 impeller you can get for ~$150 or so. The high custom pitched 550 impellers are $300+.
    1985 JS550/800 "Pretty Red": Newmiller 800, Rhaas 750 pump conv. [56.3mph gps]
    2009 1100 SJ:
    Kawi 1100 build in progress
    2009 SJ MINT:
    KP steering adaptor, Worx 228 intake [45.8mph gps]
    1987 WJ650:
    6M6, JD Intake Grate, 17/20, cheater pipe [47.8mph gps]
    1994 XiR: 830cc Superstock, PJS side draft, 13/18 swirl [53.7mph gps]
    1998 SXI PRO:
    3DR hull mods [TBD]



  7. #7
    PWCToday.com Is My Home Away From Home john zigler's Avatar
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    Re: 550/800 conversions stock pump

    Quote Originally Posted by theVetteman3 View Post
    That's some good info there John. What impeller and pipe did you use on your 800 build?
    13/18 Skat c-75 large hub swirl cut back 6mm, that I then re-worked / tuned.

    Pipe was a highly modified 650 pipe on a port matched (to cly, and pipe) manifold.

    Honestly I could care less about top speed numbers. I like hard acceleration, and an efficient pump ( Good hook up, no cavitation)
    RCJS also doing business as WATCON
    608-743-1305 9am to 5pm CST m-f
    email watcon@watcon.com

    Please visit our web sites

    new parts / products / services www.watcon.com
    used parts www.rockcountyjetski.webs.com
    thank you

    Please check out and like WATCON on Facebook

  8. #8
    PWCToday.com Is My Home Away From Home theVetteman3's Avatar
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    Chicago / Portage, MI
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    Re: 550/800 conversions stock pump

    Good to know, thanks. And I definitely agree about the low end. But it's nice to blow the doors off some skis too sometime.

    My 550/750/750 pump's 55.6 mph was a complete side effect of me putting in the best low end impeller I had tested. With that combo you can definitely have the best of both worlds.

    I know my ported 800 has a ways to go before I'm happy. That said, I did a nice long drag with a guy's new 1500 SXR in our riding group. The skis were neck and neck after a couple hundred yards. Because our engines were both still fairly new we were both keeping a bit in reserve, but I was pleasantly surprised how well I could keep up.
    1985 JS550/800 "Pretty Red": Newmiller 800, Rhaas 750 pump conv. [56.3mph gps]
    2009 1100 SJ:
    Kawi 1100 build in progress
    2009 SJ MINT:
    KP steering adaptor, Worx 228 intake [45.8mph gps]
    1987 WJ650:
    6M6, JD Intake Grate, 17/20, cheater pipe [47.8mph gps]
    1994 XiR: 830cc Superstock, PJS side draft, 13/18 swirl [53.7mph gps]
    1998 SXI PRO:
    3DR hull mods [TBD]



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