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  1. #11
    Resident Guru bored&stroked's Avatar
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    Re: 650sx best mods for low end

    The silver manifolds had those from the factory on 650sx's as well, the earlier black manifolds did not.

    I put a SP750, dual SRX 40mm SBN's, a 165psi head, Silver divertor manifold, modded and ported the stock exhaust, tried a PJS exhaust, skat 9/17 impeller, works intake grate, and 650 flywheel in my old 650sx. It was still a dog compared to a nice 701 superjet. I suggest doing cheap mods only and not wasting time and money going for all out performance.
    Last edited by bored&stroked; 09-29-2021 at 08:06 PM.
    '96 Suuuperjet: 84mm 61x, ported, B-pipe, Dual 44's, Newmiller head 220psi w/girdle, Skat big hub, footholds, AMG green hell mango matte.
    '95 Raider 701: Fiberglass not SMC, Hydrotrailer hitch, ugly purple and yellow everywhere.

  2. #12
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: 650sx best mods for low end

    Quote Originally Posted by DudeWithAJet View Post
    I already have a intake grate and a high compression head.
    I am curious which head you are using and the compression
    that you have measured?

    Hopefully it isn't a Ocean Pro head. The really bad 650 head
    set-up was an OP head and a .040" head gasket. They needed
    the thick head gasket just to keep the compression near 175psi,
    but the squish was close to .120".

    Stock compression for a 650 was 165psi, and I believe the TS
    was 10 psi greater @175psi. Safe for pump gas is ~185psi,
    but if you have a cheap compression gauge your measurements
    can be 30psi low.

    So 165psi with a cheap compression gauge has the potential of
    actually being 195psi.


    Bill M.


    Quote Originally Posted by bored&stroked View Post
    I put a SP750, dual SXR 40mm SBN's, a 165psi head, Silver divertor manifold, modded and ported the stock exhaust, tried a PJS exhaust, skat 9/17 impeller,
    I like your choice for carbs.

    The PJS pipe needs to turn ~6800rpm to make peak hp.
    Horsepower == Speed, RPM != Speed



  3. #13
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    Re: 650sx best mods for low end

    Quote Originally Posted by bored&stroked View Post
    The silver manifolds had those from the factory on 650sx's as well, the earlier black manifolds did not.

    I put a SP750, dual SRX 40mm SBN's, a 165psi head, Silver divertor manifold, modded and ported the stock exhaust, tried a PJS exhaust, skat 9/17 impeller, works intake grate, and 650 flywheel in my old 650sx. It was still a dog compared to a nice 701 superjet. I suggest doing cheap mods only and not wasting time and money going for all out performance.
    I prepared a very similar 650sx with a 750 and Coffmans wet pipe. I could not get the Kawasaki 140 pump to pull as hard below 15mph but from there on it was the same as a wet piped 701 superjet in a drag race. The old 650 is a lot harder to turn and stay on top of around a race coarse.
    What exactly does the IJSBA do?

  4. #14
    PWCToday Newbie DudeWithAJet's Avatar
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    Re: 650sx best mods for low end

    Also, it seems like I’m not getting enough water through the system. The water just kind of lightly sprays out and doesn’t really have any water coming out of the pisser at idle. Do you have any ideas of what could be doing that? I feel a slight vibration with the stock prop so I’m thinking maybe slight cavitation?
    Last edited by DudeWithAJet; 09-30-2021 at 04:19 PM.

  5. #15
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    Re: 650sx best mods for low end

    Quote Originally Posted by DudeWithAJet View Post
    Also, it seems like Iím not getting enough water through the system. The water just kind of lightly sprays out and doesnít really have any water coming out of the pisser at idle. Do you have any ideas of what could be doing that? I feel a slight vibration with the stock prop so Iím thinking maybe slight cavitation?
    '
    The engine gets its cooling water from the jet pump so there's your answer. The stock impeller is garbage, its made to cavitate while overloading the engine.
    What exactly does the IJSBA do?

  6. #16
    PWCToday Newbie DudeWithAJet's Avatar
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    Re: 650sx best mods for low end

    didnt see this until now, it has a west coast high compression head and ~180 psi

  7. #17
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: 650sx best mods for low end

    Pick an impeller and build around it.

    There were 3 generations of Skat Trak 650 impellers. The first two
    generation impellers contributed to many limited, and mod 650's seizing
    while doing a wide open throttle (wot) run.

    If you want to build a limited (pipe, exhaust manifold, carb, head,
    impeller, advanced timing, bored nozzle), or a modified (porting, pipe,
    exhaust manifold, carb, head, impeller, CDI ignition, advanced timing,
    bored nozzle) only the Skat Trak (3rd gen) 8/16, or 9/17 are suitable.

    The first two generations of Skat Trak impellers loaded the engine down,
    reduced rpm, increased heat, and increased the possibility of a WOT
    seizure on 650 limited and mods.

    But the Skat Trak Gen 1 (straight pitch) and gen 2: 3-degree variable
    pitch impellers can still be fun to ride
    if you keep the stock 34mm carb,
    compression below 185psi, TS650 exhaust manifold and stock pipe.

    Regarding the stock pipe, it is a POS.

    Quote Originally Posted by Benflynn View Post
    More compression, good impeller, sbn44, fiber reeds, cheater mod w/4-5” length added, h2o inj
    Benflynn is correct, the stock pipe is too short. But if you add length to
    that pipe (in the mid section) it will still be a crappy pipe, but the tuned
    length will be close to what it should have been.

    The best set-up I am aware of for a modified stock pipe is to add the
    TS exhaust manifold, TS cyl. head, bored nozzle and an 8/16 impeller.
    All other 650 impellers are too big. This set-up is competitive in a stock
    class. Stock class rules will often allow an aftermarket carb like a 44mm
    Mikuni.



    Bill M.
    Last edited by wmazz; 10-04-2021 at 03:13 AM.
    Horsepower == Speed, RPM != Speed



  8. #18
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    Re: 650sx best mods for low end

    I remember in the early 90s everyone was recommending a straight 16 degree impeller. This was way too much load when a straight 15 was about right. They would vibrate a little out of the hole but were fine once you were moving. The 8/16 and 9/17 were smoother, the Solas "A" 13-18 was very good as well. These are all old and most 650 props and shafts are chewed up by now. Anymore use a 750ss driveshaft and modified 750 impellers, Concord or big hubs, for 650sx applications. A Concord 11-16 or Skat 8-16 large hub is great for 650s.
    What exactly does the IJSBA do?

  9. #19
    PWCToday Regular IamMikeM's Avatar
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    Re: 650sx best mods for low end

    Don't forget a lightened flywheel! Those make a noticeable difference.
    87 X2 650, Bad Bones head and reeds. Mariner ex manifold, Coffmans stainless steel pipe, Mariner waterbox, Jetinetics flywheel, Dales Bad attitude ign, Westcoast intake, SBN44, K&N flame arrestor, TRD throttle wheel, Bullettproof stem, Renthal bars, KVPI finger throttle, Mariner deep intake grate. Dual cooling. billet coupler set, Scat Trak 8-16, Blueprinted and extrude honed pump. PJS rip turn. 1.5 chop.

  10. #20
    Resident Guru bird's Avatar
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    Re: 650sx best mods for low end

    My TS650 with only a 44SBN and Impeller will pull two people out of the hole without issue and go all the way to 35mph. The biggest difference was getting a brand new Skat from Impros. I went with the 10/18. I also have the silly Prowatercraft pump tunnel mod too. The small 28mm carb was the biggest bottleneck for low end grunt.
    Third Coast Freeride - Midwest Wave Warriors

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