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  1. #1

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    Does this make sense to anyone? (nozzle testing)

    I've tested a couple nozzles and nothing is making sense. The most recent is this:

    Test A:
    15/20 prop, 83.5 nozzle (stock), 11 psi boost, 1/2 tank of gas, 75.2 mph, 8250 rpm (all over the limiter)

    ...so I drop the nozzle down to a 79, add some boost, and fill up the tank with gas and I get...

    Test B:
    15/20 prop, 79 nozzle, 12 psi boost, full tank of gas, 74.7 mph, 8150 rpm

    So basically, it did a good job of dropping the rev's, but I lost speed with an increase in power. Weird. Just FYI, with the stock 83.5 nozzle and a 15/21 prop, I was able to go 77.5 mph at 10 psi boost.

    What are you guys seeing when you change nozzles?

    Mike


  2. #2
    Got Boost? psycho rxp's Avatar
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    now it's too restricted. U will need to open it up to probably an 81mm nozzle,and de-pitch the prop to 8100-8150. Keeping it off the limiter with the nozzle u want to run will get u the best speed reading for that prop.

  3. #3
    Matthew K ReDevilRXP's Avatar
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    Quote Originally Posted by psycho rxp View Post
    now it's too restricted. U will need to open it up to probably an 81mm nozzle,and de-pitch the prop to 8100-8150. Keeping it off the limiter with the nozzle u want to run will get u the best speed reading for that prop.
    Yeah im not expert, but i think your changing to many things around at one time, to many variables. Like psycho said i would put the 81mm ring in then pitch the prop to 8150....

  4. #4

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    Quote Originally Posted by engineermike View Post
    I've tested a couple nozzles and nothing is making sense. The most recent is this:

    Test A:
    15/20 prop, 83.5 nozzle (stock), 11 psi boost, 1/2 tank of gas, 75.2 mph, 8250 rpm (all over the limiter)

    ...so I drop the nozzle down to a 79, add some boost, and fill up the tank with gas and I get...

    Test B:
    15/20 prop, 79 nozzle, 12 psi boost, full tank of gas, 74.7 mph, 8150 rpm

    So basically, it did a good job of dropping the rev's, but I lost speed with an increase in power. Weird. Just FYI, with the stock 83.5 nozzle and a 15/21 prop, I was able to go 77.5 mph at 10 psi boost.

    What are you guys seeing when you change nozzles?

    Mike

    Mike you past the sweet spot...More preasure BUT not enough volume to push the ski 81 sounds about right....82 with good accel.


    You need to pitch to 1 size and then play with it with nozzles.

  5. #5
    Yeah, I thought I remember reading per Dan (JD1) that the 79mm isn't good until you're making enough power to pass the 90mph mark. This true?

  6. #6
    Site Admin Green Hulk's Avatar
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    Mike, run the 81 mm nozzle and pitch your impeller for optimum RPM's with that ring in place. You will see your best performance this way.

  7. #7

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    I appreciate the advice, folks.

    A little background to explain why I did what I did. . .

    With the turbo and F/IC, I'm able to dial in all the power I need (up to about 25 psi boost), but I can't run any more than 8100 rpm because of the stock ECU. My goal is to get the rpm as low as possible, then get back up to 8000 rpm by raising the boost. Another way to do this is to raise the boost, then play with the nozzle and prop to get the rpm back down. I thought a 15/20 with a 79 mm nozzle would drop the rpms quite a bit (which it did), then I could raise the boost and go even faster (which it didn't).

    This was sortof a temporary fix anyway. I have a prop out at IMPROS being polished and pitched to 15/24. If that works with the 83.5, I'll just bring my 81 and 79 mm nozzles to the river and do back-to-back testing then.

    Mike

  8. #8
    West Texas RXP skoepp's Avatar
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    Quote Originally Posted by engineermike View Post
    I've tested a couple nozzles and nothing is making sense. The most recent is this:

    Test A:
    15/20 prop, 83.5 nozzle (stock), 11 psi boost, 1/2 tank of gas, 75.2 mph, 8250 rpm (all over the limiter)

    ...so I drop the nozzle down to a 79, add some boost, and fill up the tank with gas and I get...

    Test B:
    15/20 prop, 79 nozzle, 12 psi boost, full tank of gas, 74.7 mph, 8150 rpm

    So basically, it did a good job of dropping the rev's, but I lost speed with an increase in power. Weird. Just FYI, with the stock 83.5 nozzle and a 15/21 prop, I was able to go 77.5 mph at 10 psi boost.

    What are you guys seeing when you change nozzles?

    Mike
    I ran a 82 mm nozzle yesterday with no other changes and exact same rpm 8,100. The day before i ran the 83mm and was a tick faster top end and 8,100 rpm. go figure.

  9. #9
    Quote Originally Posted by skoepp View Post
    I ran a 82 mm nozzle yesterday with no other changes and exact same rpm 8,100. The day before i ran the 83mm and was a tick faster top end and 8,100 rpm. go figure.
    RAD

    How were the weather conditions each day? Humidity, temp, etc. You can gain and lose 100 RPM easily with stage 2 and up setups. I would turn 7900 RPM one day last summer and the very next be running 8000 RPM and to me the weather didnt change much, but after looking at the humidity, temp, dew point, etc the day before and compared I understood where the difference came from.
    Last edited by RXP-REX; 04-14-2008 at 01:11 PM.

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