Hull Questions 650sx..

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  1. #1
    Resident Guru sportsfreak29's Avatar
    Join Date
    Oct 2011
    Midland, Tx.

    Hull Questions 650sx..

    Ok, so I'm doing a big revamp ony 650sx, trying to get the hull to hook up better and take some of the slide out of it.

    A member on here, "Timothy", had mentioned removing the out edge chine from the hull bottom, but never gave any detailed information on why or what changes it would make to the handling.

    Hoping he's still around or maybe someone else might have an idea of what he was getting at.

    I'm looking at chopping the back of the ski 1.5", in the process of doing a strake mod, installed a rear exhaust, outer walls of the engine bay are being reinforced, bond rail cut at the hull near the front running back to the center of the engine compartment and reattatching them with an upward curve like a Rickter, chopping the back tray for a X2 trim.

    Lots of mods, but I did look at the hull bottom's outer edge closely. It has a very different geometry than the JS hulls, which seem to carve much better, and don't tend to slide out, if anything they would rather high side your ***.

    Thought about sanding them flat, or filling the outer part of the recess, so there is a sloping flat surface that is deeper closer to the inner chine and doesn't have a sharp lip on the outer edge.

    Please advise, thanks.
    Last edited by sportsfreak29; 01-08-2019 at 03:38 PM.
    If you're not crashing, then you're not trying!!!

    '90 650sx, full mod with all the bells and whistles.
    '84 JS550/650 pump swap with Viper 9000 motor.
    '93 550sx with a 650sx motor and Rhass pump kit.
    '81 JS440, full mod 550 PP motor. '
    '93 300sx/750 SP BOB.

    Special thanks to Chris Newmiller, the guys at Prowatercraft Racing, Rhaas Products, and Mitchell at M&M Marine!

  2. #2 Is My Home Away From Home theVetteman3's Avatar
    Join Date
    Jul 2008
    Chicago / Portage, MI

    Re: Hull Questions 650sx..

    The 650sx hull is the hull that taught me how to carve! If you get that thing leaned over it does pretty well, and stock for stock, I personally found way more predictable than the 550 hulls. If you steer flat it will slide out in a second. That's the first hull which I was able to ride and carve around on with a stock ride plate. Since my 650sx/750 I used to have was set up all for low end, I wanted to be able to spin the rear and get the nose high for tricks. I can't ride a 750 or especially 550 hull with a stock rideplate.

    I wouldn't trust Timothy. I don't personally know him, but reading what he has posted over the years, I personally believe he has a few bolts loose. I think that's the kindest way I can put things so I'll stop now.

    Ok now lets talk your mods. What exactly do you want, freestyle/ tricks, carving, or a mixture of both? Those mods are pretty involved, and you definitely want to know what each does before you do them. First, I would without a doubt leave the bottom and corners of the hull alone. At least don't cut anything off. If you cut any chines or strakes off, the ski will slide like crazy. I have no idea what Timothy was talking about, but if you remove an edge, you will slide. As you mentioned the strake mod, making them taller/ deeper will make the hull grip a bit harder. This would be a good mod. The sxi pro, sxr, and 08+ SJ are good hull bottoms to reference for this. Guys do this a lot on 550 hulls. Just don't go too far forward, or else it will impact steering.

    Chopping the rear of the hull will make the nose ride way higher. This is good for freestyle bad for carving. For carving you want the nose of the ski as planted as you can get, for more front grip. Getting the nose high is good for low speed turning, to get the nose up higher.

    I really liked my 650sx/750. I have a build thread if you haven't seen it. If I built one again, the first thing I would do is put prowatercraft tubbies on it. The added side pressure really helps with making the steering and carving more responsive. In my mind, doing this is more worthwhile than any other mod to the nose of the ski unless you are jumping big waves or back flipping. I'd probably start there and get a few ride plates I could swap between depending on the mood I'm in. D cut stock for freestyle, long jet dynamics for carving. The strake mod would be a great thing to do as well.

    Hope that helps, and good luck!
    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
    Top Dog bandit88's Avatar
    Join Date
    May 2014
    Green Bay WI

    Re: Hull Questions 650sx..

    650 hooks up good, just need to throw a leg off the side and pitch it. Jeff jacobs was a slalom beast on a 650. The only things I can really recommend is a slightly shorter pole, and sharpen the chines on the bottom. You can take a pvc tube that matches inbetween the chines pretty good, wrap it in sandpaper and sand till the edges are sharp. The mods you are doing to the bond rail will not help it stay hooked in corners. Also, Vetteman said it best, Timothy has a few bolts loose, dont listen to a word he says.
    Last edited by bandit88; 02-05-2019 at 10:57 AM.
    -95 750SXI
    -86 440 with PJS800 conversion -
    -90 TS650
    -81 JS440
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