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  1. #1

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    Counterintuitive nozzle results. . . again.

    I once again tested a smaller nozzle, and once again got results opposite of everyone else.

    To recap, a while back I tried home-made (welded and lathed) 79 and 81 mm nozzles. Using the stock 83 mm nozzle and a 14/19 prop re-pitched to 15/20 I went 75.2 mph at 8250 rpm banging the limiter. I put in the 81 mm nozzle and went 73.5 mph at 8200 rpm. I then put in the 79 mm nozzle and 73.7 mph at 8050 rpm. It seemed to me that the smaller nozzles do, in fact, reduce engine rpm, but also reduce speed.

    I figured that my welded and lathed nozzles were probably the wrong geometry, surface finish, or something, so I bought an 81 mm ring and installed that instead.

    This past weekend I tested again. With a 15/20 re-pitched to 15/24 and the stock 83 mm nozzle, I went 79+ mph at 8100 rpm and 12 or so psi boost. I installed the 81 mm nozzle and raised the boost to 13-14 psi. While fully expecting 81+ mph at 8100 rpm, I was disappointed with 7800 rpm and could barely break 75 mph. What a terd. No, the supercharger washers are not slipping .

    So. . . twice I've tried smaller nozzles than stock and twice it slowed down.

    It is possible that my little T3 60 trim turbo is simply out of breath. In some rare turbo cases, raising the boost can actually cause a loss of power. This week I plan on going out and doing some back-to-back runs at different boost levels and see if that's the case. If I can't get back to at least 79 mph, then I'm writing off reduction nozzles alltogether.

    Mike
    Last edited by engineermike; 05-27-2008 at 08:06 PM.


  2. #2
    what ecu are you running? Maybe it has something to do with the amount of boost at the ecu changing the timing

  3. #3

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    =d> It Is Nice To Read Your Post Because You Give Us All The Info We Need.todd

  4. #4

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    Quote Originally Posted by miamirider View Post
    what ecu are you running? Maybe it has something to do with the amount of boost at the ecu changing the timing
    I'm on the stock ECU. Normally I'd agree with that being a possibility but 9secZO6 is running 15+ psi on the stock with pretty good results and also my ECU doesn't "see" more than 7.5 psi because I clamped the MAP sensor signal.

    Mike

  5. #5
    JD 1's Avatar
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    Quote Originally Posted by engineermike View Post
    I once again tested a smaller nozzle, and once again got results opposite of everyone else.

    To recap, a while back I tried home-made (welded and lathed) 79 and 81 mm nozzles. Using the stock 83 mm nozzle and a 14/19 prop re-pitched to 15/20 I went 75.2 mph at 8250 rpm banging the limiter. I put in the 81 mm nozzle and went 73.5 mph at 8200 rpm. I then put in the 79 mm nozzle and 73.7 mph at 8050 rpm. It seemed to me that the smaller nozzles do, in fact, reduce engine rpm, but also reduce speed.

    I figured that my welded and lathed nozzles were probably the wrong geometry, surface finish, or something, so I bought an 81 mm ring and installed that instead.

    This past weekend I tested again. With a 15/20 re-pitched to 15/24 and the stock 83 mm nozzle, I went 79+ mph at 8100 rpm and 12 or so psi boost. I installed the 81 mm nozzle and raised the boost to 13-14 psi. While fully expecting 81+ mph at 8100 rpm, I was disappointed with 7800 rpm and could barely break 75 mph. What a terd. No, the supercharger washers are not slipping .

    So. . . twice I've tried smaller nozzles than stock and twice it slowed down.

    It is possible that my little T3 60 trim turbo is simply out of breath. In some rare turbo cases, raising the boost can actually cause a loss of power. This week I plan on going out and doing some back-to-back runs at different boost levels and see if that's the case. If I can't get back to at least 79 mph, then I'm writing off reduction nozzles alltogether.

    Mike

    something doesnt add up right
    my wifes RXP is SC but has a Skat 15/19 bent 2.5+mm with a 79mm nozzle and runs way over 80mph @ 8150R's, sounds to me its almost the same setup just lose of speed, is it a RXP?

  6. #6

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    Quote Originally Posted by JD 1 View Post
    ... is it a RXP?
    Yes, an '04. In the same hull, I went 75.0 mph with a simple Stage 1 + RR impeller on the 14/19 re-pitched to 15/20 and stock nozzle.

    Mike

  7. #7
    kp04rxp's Avatar
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    Quote Originally Posted by JD 1 View Post
    something doesnt add up right
    my wifes RXP is SC but has a Skat 15/19 bent 2.5+mm with a 79mm nozzle and runs way over 80mph @ 8150R's, sounds to me its almost the same setup just lose of speed, is it a RXP?
    Mike these nozzles confuse me also especially since beachbum has been running over 80 with the stock 87mm x nozzle when riva recommends the 82mm i think... I also noticed after adding my ecu that my 81mm nozzle was actually choking down the ski enough to cause it to porpoise at all different speeds... is this possible?

    On another note,

    Jd1 what are the specs on your wifes ski... curious because I am currently trying to dial my stage 3 rxp in.. right now I'm working with an 83mm ring 15/20r prop untouched.. 8450-8500rpms

  8. #8
    I like Boobs. wetwolf's Avatar
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    Quote Originally Posted by kp04rxp View Post
    I also noticed after adding my ecu that my 81mm nozzle was actually choking down the ski enough to cause it to porpoise at all different speeds... is this possible?
    Yes, it's possible.

    Mike, have you tried an 85mm nozzle with the 15/20??

  9. #9
    JFizzleJR's Avatar
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    Quote Originally Posted by JD 1 View Post
    and runs way over 80mph @ 8150R's


    Sorry, couldn't resist.

    The only thing I've noticed is that a good range for most of these skis is 80mm-83mm. Anything more or less and your sacrificing either holeshot or top speed on most applications. Could you have bent the prop in a way that causes an abnormal flow of water (therefore altering its efficiency in an unknown fashion)? Sorry if you already posted this, but have you tried an out of the box 15/20R instead of your re-worked 14/19? How about a 15/19R 3 blade?

  10. #10
    Website may not be suitable for small children WOT's Avatar
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    Mike, just some thoughts about what could be happening....

    When you go to the smaller nozzles, the internal pump pressure goes way up and loads the prop, which is to be expected. But, it seems almost as if you have something strange going on with your prop. Maybe the at the higher internal pump pressures the prop is flexing under the load and is becoming inefficient. It might be possible that it is flexing in a manner that keeps the pump loaded and the rpm down, but reduces the amount of water that the pump is processing, so your speed suffers as well. How is your wear ring clearance? Are you running a SS wear ring? Do you have another prop you could test with?

    I just thinking out loud here because your results seem strange to say the least.

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