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  1. #1
    Student of Speed rxpwhistler1's Avatar
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    Nov 2007
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    Oakland County Michigan
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    708

    Make sense out of this!

    Mods:
    42lb injectors
    XS intercooler
    Greenwheel SC impeller
    Shorty Waterbox
    Riva tip
    Groco Strainer
    Riva Grate
    Riva Adjustable nozzle (83 ring in for 8100 RPM'S)
    2 Degree Wedge
    Catch can breather
    Riva 4" Rear Intake
    Dynotune boost gauge
    4-Tec performance IC blockoff plate
    Denso Plugs

    GPS-Garmin GPS72

    Boost was 9.7lbs at 8000-8100 RPM
    Water-little chops but not bad
    Fuel-3/4 full
    Rider-170lbs

    Rpms were at 8000 full throttle with flashes of 8100. I did three runs and my gps was reading..71 tops. And it took a while for it to get to that speed. I can't figure out what the hell is going on. No boost leak according to the gauge, rpm's are about right....nothing dragging. I had the trim in the middle.

    Is my gps jacked or is my ski jacked?!!?!?!?!


  2. #2
    Student of Speed rxpwhistler1's Avatar
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    forgot some mods

    filled rideplate holes, 15/20R out of the box, and SS ring, RE blockoffs. Forgot those mods.

  3. #3
    dv8rxp's Avatar
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    May 2005
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    Man that cant be right. with your prop/pump set up, and 8000+ rpm should be around 77mph. For it to be only 71mph there would have to be something dragging, or a pump leak between the pump and nozzle, or a bad gps.

  4. #4
    Vern's Avatar
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    Grand Haven, MI
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    Agreed ... I have not heard of a bad GPS before, but phew ... you should be 75 - 77 mph. Take a very good look at the bottom of your ski ... pull on your grate a bit, make sure your grate and rideplate are level with each other and that the grate inserts are solid. Stick your fingers up past the grate ramp, make sure your plastic pump shoe is all there and solid ...

    Boost is good, rpms good, parts list is good ... I think something is funny with the bottom of the ski that is really slowing you down. Take a look, and take a picture of the bottom if something looks wrong, and post it if possible ...

  5. #5
    Student of Speed rxpwhistler1's Avatar
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    Vern and Greg

    Quote Originally Posted by Vern View Post
    Agreed ... I have not heard of a bad GPS before, but phew ... you should be 75 - 77 mph. Take a very good look at the bottom of your ski ... pull on your grate a bit, make sure your grate and rideplate are level with each other and that the grate inserts are solid. Stick your fingers up past the grate ramp, make sure your plastic pump shoe is all there and solid ...

    Boost is good, rpms good, parts list is good ... I think something is funny with the bottom of the ski that is really slowing you down. Take a look, and take a picture of the bottom if something looks wrong, and post it if possible ...
    I def should be seeing 77-78 forget 75! Everyone close to my setup with less stuff are running those speeds. I think you bring up a good point vern. I also am going to try and run the 81 ring vs the 83 that in now. Jerry said my boost seems low for my setup. I am going to do a boost leak check also.

  6. #6
    double post...moderator please delete this post...thanks!

  7. #7
    Sean, was this ski winterized and if so how? How old is the gas that's in it? I dont care if there was Sta-bil in it. This was only your second ride this year right? I've always noticed my speeds are down a bit until I go through 2 full tanks of fuel. When my ski was stock after its first winterization it wouldnt run over 64-65mph for the first 2 tanks. After it was a stage 1 and proved to be a 71+mph ski it wouldnt run faster than 67mph after the next winterization til I went through 2 tanks of fuel. We'll see how my first couple rides go this year, I expect it to be the same situation.

    Also I agree with Vern. Check the hull. How are your OPAS blocks? Are they flush or stepped up a little? Make sure they don't hang below the hull. Also, check the intake grate. Can you pull it down? Maybe one of the bolts is sliding and at speed the grate is dropping down? Also, when running are you sucking in air through the carbon seal? I have heard of this happening, and since you got your ski used it could be time for some general maitenence where the driveshaft goes thru the hull? Then again your RPM look good. Just throwing that out there, I doubt that's the problem.

    I'm sure it's something simple, keep your head up. I'm willing to bet it's a boost leak. I had the same issue last summer. I had a full stage 2 and couldnt go faster than 68mph. I had to reseal the stock IC blockoff with silicone. Once I did that I only gained 100 RPM, but my speeds went from 68mph to 73+mph. Just that little thing cost me 5mph! Come to think if it now I bet a boost leak is your problem! Might not be the IC blockoff, but could be a IC pipe or anything.

    When are you going out to test next? If you need some help I may be free for a day this week. Maybe I can stop by your place and head out with you, check things over. Let me know!

  8. #8
    dv8rxp's Avatar
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    I don't understand how a boost leak could be the problem. 8000 rpm is 8000 rpm, boost leak or not. the rpm and his pump set up should equal x amount of speed, unless there is a pump problem or a drag problem. If you were having rpm issues, then I would chase a boost leak, but this is not the problem.
    Last edited by dv8rxp; 04-21-2008 at 05:49 PM.

  9. #9

    Join Date
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    Having your trim in the middle is not the magic position. I would check the trim adjustment as well as the bottom of your ski. Are you running the vts extension rod? If your middle position was the fastest position before you added the wedge. The fastest now going to be a little higher.
    Good luck.....

  10. #10
    Quote Originally Posted by dv8rxp View Post
    I don't understand how a boost leak could be the problem. 8000 rpm is 8000 rpm, boost leak or not. the rpm and his pump set up should equal x amount of speed, unless there is a pump problem or a drag problem.
    Yeah, and I was at 7800 RPM...68mph...and alllllllll daaaaaayyyyy to get there. Just like he said he had as a problem.

    I sealed my IC blockoff with a FAT bead of silicone, went back out and pulled 7900 RPM 73.x mph and it got there in a HURRY.

    Maybe it's not his problem, but now that I think of it his situation sounds very similar to mine.

    Also I went back and adjusted my left OPAS blockoff and gained close to 1mph to put me at 74mph.

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