engine help! 657x

[bigdawg10132004]

Hello people. I just bought a shell of a 94 or 95 sea doo xp with the motor taken out. It is a 657x (frozen up) and I wondered if boring and rebuilding would be better than buying another motor for this baby. Also, how much bigger could I go with an engine while still being able to use the existing motor mount positions.
Thanks.
Sea Doo nubie!

[WATERCRAFTSERVICES]

Re: engine help! 657x

Look at the last two numbers on the VIN plate that will tell the year. Most likely 93-94 with a 657. It is much more economical to purchase a remanfactured engine from SBT than to do it yourself unless you have access to the proper machining tools needed for boring and crank rebuilding. If it is frozen then the crank is most likely shot and you will need cylinder work too. There are alot of little things that will add up quickly when doing it yourself. And then you have no warranty if something goes wrong. If you want to go with a bigger cc the 720 is the only other option. Not really an option either because you will need 720 electrics,carbs and exhaust to go woth. And if you decide to go with SBT they only accept the same core that you are receiving in return. Order a reman, install it yourself. Save money and time.

[Murymann]

Re: engine help! 657x

I made the BIG mistake of DIY rebuild in '02 for my 97 XP using "friends" and parts from PP and other sources. Expensive..and what a cluster getting it "right". In 03 the 657X in my 94 XP went away and I bought a reman from SBT. It's wasn't cheap, but it runs great. Follow break-in instructions to the letter and you'll have a strong ride.

[bigdawg10132004]

Re: engine help! 657x

thanks a million guys. Is the 720 the largest that will fit? Also, if I simply get another 657x and do some impeller research and combinations, I should be able to speed things up a bit without the extra ponies you think?

[Technical Support]

Re: engine help! 657x

Be aware there is only a few HP between the 657x and 717 - and we only do even swaps.

[dsolie]

Re: engine help! 657x

Yhea, with a F/A and Rejet kit, repitch your prop you can wake up that 657x nicely! Add a westcoast head and even better. You can keep up with those 720's.

[bigdawg10132004]

Re: engine help! 657x

Yhea, with a F/A and Rejet kit, repitch your prop you can wake up that 657x nicely! Add a westcoast head and even better. You can keep up with those 720's.

:emoticonb :emoticont

Thansk a million!!! I was gettin discouraged thinkin about it today, so I went outside and cleaned up the hull and came in to check the post. Very encouraging. I want a ride that will be quick and responsive and not to mention to beat the yamahas and other rides!!!!
Should I go with a bore increase along with maybe an aftermarket exhaust and induction? Or would the impeller change, F/A and head combination get me what I am seeking....going on the water with my hair on fire!!
I am realisitc, I know I won't be able to mess with the big boys, but at least 50 - 60 MPH is what I am shooting for!

[Murymann]

Re: engine help! 657x

There are only three basic fundamentals to "go-fast" both on land and on the water. First and most important: make the engine breath as best you can. Second, put what power you have to work as best you can. Third, cut drag as much as possible.

Improving air flow and burn efficiency will boost HP and torque. Torque does the work & HP gives you speed. If you are spending dough, start here. Rotax designed these engines for the most bang while remaining (reasonably) stable. Some here will disagree with me, but I say unless you NEED to punch-out the whole top end, limit your playtime to aftermarket bolt-ons (high-flow heads, flame arrestors & exhaust, carb rebuild & rejetting) and "leave the sleeves" alone. Assure even fuel burn by keeping your ignition system in top shape and run the 'right' plugs. Before the bolt-ons, make sure your bottom end is solid. More flow means more revs so keep the limiter, or you'll be rebuilding very soon.

Put the ponies to work by getting water in and out of the Jet Pump efficiently and quickly. "Worx" grate, SS prop and a "performance" rebuild of the jet pump will give you great results. I like the Formula pump, but watch those wear-rings! When choosing a SS prop, don't go nuts. One degree higher pitch will give you 'ok' top end improvement, IF she's hooking-up (flow to the pump) and breathing right. Don't let anyone pitch you up over 2 degrees. You'll be very unhappy with how the Ski crawls out of the hole and your midrange “snap” goes away. Over pitching will also “lug” the engine and she can't deliver maximum power unless she is revving in the “right” RPM range at a given speed.

Lastly; the "right" sponson & ride plate combo will improve ride angle and give you proper air flow under the hull (in the right places) to decrease your drag. This gets tricky and you'll just have to play with it. Some long-time racers and performance builders here can help you has they did with me some years back when I did some tweeking on my XPs. But, you CAN do the basics yourself which is to ALWAYS keep the hull clean, scratch-free and slippery. Start with a good compounding and buff-out with 3M Microfine. If you can't afford the new copolymer or Teflon-based 'slippery agents', apply several coats of a high-quality wax to seal your work. I use Maguires Pure Boat & RV wax on both my boats and XPs.

A strong running 657X dual carb will keep up with and often TOAST older non-DOO brands of skis running 700 to 750CC stock engines and there is just NO comparison to an older XP hull for handling. That's why I keep these old XPs. They are just flat-out 'fun' to ride.
Good luck!

Bob