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  1. #1

    Cool GTX Di 2002 951 Compression

    Could I be loosing compression through the rave valves? I am not sure how they work.


    Am Getting 110psi on each cylinder.


    What should i do to get more compression?


    The ski is only doing 48mph any advise?


  2. #2
    KrunchovXPL-GTX-RX's Avatar
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    First of all, the RAVEs have absolutely no effect on static compression since the blades do not actually touch the piston/rings.

    How they work is that they simulate a lower exhaust port timing for better low/mid range performance and then are opened via exhaust pressure (787) or by the MPEM (947-947DI) at a certain RPM. By opening they allow the engine to operate at the true exhaust port timing which is better for high RPM performance.

    That said, there is a lot that goes into the compression reading you get at any given time. The strength of the starter/battery for one, as well as the gauge used, altitude, and temp of engine (which changes it a bit). Typically, you are looking for a variation of say more than 5-6% (those are my numbers) to indicate a problem. Did you lock the throttle wide open before doing the test? This keeps the injectors from firing on a DI.

    So, in that case, let us put the comp readings aside for a moment and let me ask:

    How are you measuring the speed?

    What RPM is it turning at this speed?

  3. #3

    Unhappy

    How are you measuring the speed?

    What RPM is it turning at this speed?
    i let you know on Friday what are the RPMs

    i measure thru the GPS


    Anyone have and great tip for speed up a 951 engine? cleaning any part? upgrade anything? remove any part? what type of gas you guys recommend?

    What I've done.

    i got new battery ... i bought the original spark plus brand new ... i flush the oil and insert the oil that seadoo recommends... i clean the rave valves... i changed the jet pump oil ... i put grease on the drive shaft bearing

    There is something me should i do so i can perform better?

  4. #4
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    951's

    you can have all sorts of problems with 951's

    check that rave's are clean and opening

    check water box regulator for holes in the diaphram

    First thing I'd check is the prop however..that's where I find most problems on skis that don't go as fast as they should. ( has alo to do with our area, lots of gravel filled shorelines)

    you'll find plenty of talk here about 951 issues and answers too.

  5. #5
    Work Harder, Millions on Wellfare Depend On Us! ultramaxracing05's Avatar
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    The man that knows his shit is Krunch he's helped me out alot on my ski.
    he will guide you the right way.

  6. #6
    any more great tips?

  7. #7
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    at this point

    you should read everything on the board about the various 951 issues that have been asked and solved.

    you can gain 4-5mph by losing 100 pounds....

  8. #8
    KrunchovXPL-GTX-RX's Avatar
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    I just realized that it is an '02

    Ummm, 48 is not that slow for that boat.

    You are limited in what you can do as far as performance because it is a DI and you have it in the largest hull that SD ever put a 2-stroke in (that is the same hull as the GTX 4-tec but you only have 130hp VS 155-185-215-260-if you get my drift).

    You could do some stuff, by that I mean spend some money, and you would be doing very good to get it over 53.

    In other words, it is not a fast boat and will not even run with a stock NA 4-tec.

    Get back with the peak RPMs and we can see if it is where it should be. Sure 951s have some issues and there is a lot of data on here about them but most of boils down to abuse/neglect and or folks just not knowing what to do. You see them talked about a lot because SD used it in a lot of hulls between the two versions (carb and DI).

  9. #9

    Cool

    Quote Originally Posted by ultramaxracing05 View Post
    The man that knows his shit is Krunch he's helped me out alot on my ski.
    he will guide you the right way.

    and I wonder who introduced him to the fascinating world of Jet Ski's. Was that a R/R module problem on your
    'ol 95 XP Andy ?

  10. #10
    Work Harder, Millions on Wellfare Depend On Us! ultramaxracing05's Avatar
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    Quote Originally Posted by David_HX_RXP View Post
    and I wonder who introduced him to the fascinating world of Jet Ski's. Was that a R/R module problem on your
    'ol 95 XP Andy ?
    Was it you David?
    lol

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