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  1. #1

    Spx Frankenstein

    I bought a 98 gts cheap to scavenge for my spx build. Spx is a 94, wiped crank. Looking for performance tips with this particular swap. Obv I have dual carbs on the 657, one on the 720. Going to use the 720 engine. Dunno about impeller changing, maybe full housings. I’ve already put power vts on the spx. Torque and hook up are the goals, it’s my twitchy trick boat, I have several 3/4 seaters for the boring stuff. Any input appreciated, it’s all apart and ready to get a little wild.

    Edits: Typed to fast - not considering GTS impeller, potentially solas, maybe grate. Real big q's on moving dual carbys over, to 720, and if so anyone done and jet sizes they went to. tia!
    Last edited by thibble; 09-27-2020 at 06:54 PM. Reason: clairfication


  2. #2
    Myself's Avatar
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    Carb info can be found here...http://www.seadoosource.com/carbreference.html

    Also impeller specs can be found on the same site. 3 seater impellers are normally lower pitched because the ski is bigger and heavier. They usually work well on a 2 seater to give it more pop out of the hole. I would try the Gts impeller after you get it put together.

  3. #3
    Thanks! I was going by reviews of the '98 GTS that complained of a poor impeller selection choice by the factory. Pretty crazy trying to figure out what mods do what, even after reading greenhulk for hours . The 717s that came factory dual carb claimed about 85hp, and the later 717s that only came with a single claim the same 85hp. I really wanted a 951 but no good deals on donor boats. Just looking for a bit more punch, of course being able to keep up with the Mrs on her 94 RA700 would be nice but I'd need a 951 and newer hull.

    Quote Originally Posted by Myself View Post
    Carb info can be found here...http://www.seadoosource.com/carbreference.html

    Also impeller specs can be found on the same site. 3 seater impellers are normally lower pitched because the ski is bigger and heavier. They usually work well on a 2 seater to give it more pop out of the hole. I would try the Gts impeller after you get it put together.

  4. #4
    Myself's Avatar
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    Your Spx with a 717 and a decent impeller will be mid 50's. That should be about where the purple hull Raider is unless it's piped.

  5. #5
    Mid 50's would be great. The raider is 53 gps. Edit: Read up on the impeller. Looks like the 11/22 from the GTS is what was used in the 717 SPX, likely work out.

    I'm on the fence about the carbs. The 717 BN-40I single on the 717 has the accel pump. My duals on the 657 don't. The jet charts are great, I can't find online the diff between my dual BN-38 and the later model 717 BN-38I, but I think if I use the jet sizes listed in BN-38I I'd be close enough to adjust.
    I holed a piston going extreme on a stroke bike, so I'm considering rolling with the stock single and see what she does, cuz as soon as I start jetting I'm after a pipe...

    Quote Originally Posted by Myself View Post
    Your Spx with a 717 and a decent impeller will be mid 50's. That should be about where the purple hull Raider is unless it's piped.
    Last edited by thibble; 09-28-2020 at 10:12 AM.

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