93 XP 657 Porting/Pipe?

[Mark Kehoe]

Hi Guys,

I'm currently restoring a 93 XP, the engine is out for a full rebuild and while I'm at it I thought it might be a good opportunity to do some work on it to get a little more performance. The Seadoo racing handbook has some porting specs for the 657 engine, is anyone running them and are there noticeable gains? Is it worth modifying the intake ports to the same spec as the 657x and running the same rotary valve and timing as the X? Is there an aftermarket pipe that gives good gains? I believe removing the spark arrestor and re-jetting accordingly is also worthwhile doing? I know some might say just get a 657x engine but this is more about having some fun with what I've got. I know it's an old ski but I'm sure that many of you have squeezed some extra power out of these back in the day. Thanks for your help.

Mark

 

[Matt Braley]

The X is a pretty peppy engine. They are more like a 717 while the 657's are kind of "580ish" still. I know the rv timing works with the port timing so I'm not sure what gains you would get from the intake area alone. If you had the cylinders and head from an X engine I'd say go for it.

I put pipes on these things back then and all I ever got was a more offensive sounding machine that blew up soon after. I didn't know squat back then it just worked on my dirt bikes so I tried it on the skis.

Today if I wanted to make one a little edgier I'd probably bolt on a stock 717 pipe and then re-jet the carbs like the 657X. That in a combo with a correctly pitched performance prop (Solas X or K prop around 15/20 pitch for example) and you should have a notable improvement in performance.

 

[Mark Kehoe]

Hi Matt, thanks for taking the time to reply. The Seadoo porting specs in the racing handbook are still a bit of a mystery to me, widely available but yet no seems to have made the modifications? I'll look into the pipe and impeller...

 

[mikidymac]

Porting is an art and if you haven't done a lot of it on a 2 stroke don't.
I is not like cleaning up a pair of Chevy heads.
If you are not exact and precise you will never have an engine survive.
There are only a handful of guys on the planet that are good at it and have been doing it for over 20 years.
2 stroke porting is not just grab a pattern and start grinding.

 

[Matt Braley]

A normal 657 just can't take too much of a performance bump and last long. It still has that little 580 style crank.

It's not that guys have not done it but that is the very beginning of runabout racing in 93. Since the 657 did not have a lot of potential and no history folks would adapt snowmobile racing stuff to those early skis.