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657 vs. 720 exhaust + intake question

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  • 657 vs. 720 exhaust + intake question

    I put a rebuilt 717 motor in a 94 GTX I used the twin 38 carbs and intake & rotary valve cover from the 657 and I used the exhaust from the 657. I rejetted the carbs to match what a dual carbed 717 would run, don't remember now. It runs fine. I'm wondering will I get more power with a 717 exhaust pipe? Also the intake ports (on the rotary valve cover) from the 657 are round versus oval on the 717 intake I have. Should I switch the twin carbs and hardware to the 717 rotary valve cover with the larger oval ports that match the block. Is it possible to make this switch? The 717 cover I have now is for a single carb set up. It's been so long since I had the boat torn down that I don't remember. I cant believe I would have overlooked something that would have been an easy switch. Also I saw some info on bigger performance gains with a Factory Pipe. Is it worth it? I really don't want to compromise reliablity but I would like some simple go faster stuff.

  • #2
    Re: 657 vs. 720 exhaust + intake question

    YES factory pipe is Way worth it
    night and day..
    i can keep up with any stock 96xp with my hx.. and all i put on is the factory pipe and a scat prop. and i will rip any ski out of the hole..
    stock you should pull around 6700-6800 rpm and with the pipe you will hit 7200 all day.
    if you decide you want one you are in luck cause i have a new in the box one from factory pipe with everything new in wrappers.. just like it comes from factory pipe ---rev limiter/water inject.- and all the goodies
    they sell for 750 plus tax.. plus ship
    i will let it go for 400 shipped
    BRAND NEW!!!!!!!!!!!!!!!!

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    • #3
      Re: 657 vs. 720 exhaust + intake question

      and yes..
      the ports really need to match up for optimum performance..
      this is why most racers port and polish the intake and exhaust ports.. so the air has less resistance to flow thru.

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      • #4
        Re: 657 vs. 720 exhaust + intake question

        Will that pipe fit an XP?

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        • #5
          Re: 657 vs. 720 exhaust + intake question

          I strongly disagree to putting a FPP exhaust system on a GTX or a GTI if reliability is your prefference. A 718 at 7200 rpm is not what I consider "reliable", especially on pump gasoline. The hull of the GT series is much heavier than an HX or XP, and the poor little 718 would be running very hot and hard to push it through the water with a FPP exhaust system on it.

          A single carb rotary valve cover will not accept dual carb manifold, different bolt pattern for the manifold.

          If your ski runs good with the 657X pipe and the 657 RV cover on it, I doubt you will see much of a gain, if any by swapping for the 718 parts.
          Bill O'Neal <br>
          WCM
          <a href="http://www.watercraftmagic.com"

          Comment


          • #6
            Re: 657 vs. 720 exhaust + intake question

            My boat has the standard 657 pipe not the 657x pipe which I think is more of a high performance pipe. Is it still not worth the investment for the 718 pipe. Ive seen them for less than $100.00 used.

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            • #7
              Re: 657 vs. 720 exhaust + intake question

              Does your pipe have the tapered cone on the tail portion of the pipe? If so, it is the high performance pipe.
              Bill O'Neal <br>
              WCM
              <a href="http://www.watercraftmagic.com"

              Comment


              • #8
                Re: 657 vs. 720 exhaust + intake question

                Sorry for the ignorance I really don't know what to look for when you say tapered cone. The pipe becomes narrow and has a rubber gasket that attaches to the next pipe that looks like a small barrel. I'm describing this from memory. The ski is on the lift I can go and look.

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                • #9
                  Re: 657 vs. 720 exhaust + intake question

                  Take a picture and post it here.
                  Bill O'Neal <br>
                  WCM
                  <a href="http://www.watercraftmagic.com"

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                  • #10
                    Re: 657 vs. 720 exhaust + intake question

                    First try on an attachment
                    Attached Files

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                    • #11
                      Re: 657 vs. 720 exhaust + intake question

                      That is the high performance OEM pipe.
                      Bill O'Neal <br>
                      WCM
                      <a href="http://www.watercraftmagic.com"

                      Comment


                      • #12
                        Re: 657 vs. 720 exhaust + intake question

                        And a super clean engine compartment too. Looks nice!

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