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  1. #1

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    Question on nozzle size for the experts

    Hypothetical situation. . .

    Let's say you're going 81 mph with a 83.5 mm nozzle at 8500 rpm on a 15/20R prop. Now, you swap to a 79 mm nozzle, which should drop the rev's to about 8050, give or take. Assuming the boost stays the same (turbo setup), what would the speed do?

    Mike


  2. #2

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    You should drop 250-350 rpm and gain after you pitch the prop. @ 8200 I think you'll drop 1-2 mph

  3. #3
    Just my opion, through much gps testing I have found that anything under 100 rpm dose not affect speed enough worth worring about (less the .2 mph)

  4. #4
    2006 RXT dave262626's Avatar
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    Speed will go up a little assuming you have enough power to hold the RPM's.

  5. #5
    Quote Originally Posted by engineermike View Post
    Hypothetical situation. . .

    Let's say you're going 81 mph with a 83.5 mm nozzle at 8500 rpm on a 15/20R prop. Now, you swap to a 79 mm nozzle, which should drop the rev's to about 8050, give or take. Assuming the boost stays the same (turbo setup), what would the speed do?

    Mike
    Mike, just out of curiosity why the 79mm nozzle? Isn't everyone losing speed with that one and giving up to much acceleration? Heard the best was the 81mm nozzle then repitch prop to get back to ideal RPM for best speed.

    But if I had to guess I would agree with Jawz, probably a 2mph loss. You're getting too far away from the optimal 8500 RPM with say a Riva ECU and the 79mm nozzle has been proven to be too small.

  6. #6

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    Quote Originally Posted by RXP-REX View Post
    ...optimal 8500 RPM ..
    Well, my point was that 8500 rpm isn't necessarily optimal. The stock style motor with external intercooler and an upgraded centrifugal supercharger builds boost and power with rpm. It makes more power and boost at 8500 rpm than it would at 8100 rpm. However, the turbo motor will have a power curve similar to the NA 155 hp motors. It will peak much earlier than the upgraded SC motor.

    The bottom line is that I'm trying to figure out the best combination to get 85+ mph at <8100 rpm. Right now I'm running a 15/20R prop and the stock 83.5 nozzle. I'm at the limiter at 10 psi boost and 77.5 mph.

    Mike

  7. #7
    Quote Originally Posted by engineermike View Post
    However, the turbo motor will have a power curve similar to the NA 155 hp motors. It will peak much earlier than the upgraded SC motor.
    Good point.

  8. #8
    JD 1's Avatar
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    you want the truth or do you want me to sugarcoat it?

    Quote Originally Posted by engineermike View Post
    Well, my point was that 8500 rpm isn't necessarily optimal. The stock style motor with external intercooler and an upgraded centrifugal supercharger builds boost and power with rpm. It makes more power and boost at 8500 rpm than it would at 8100 rpm. However, the turbo motor will have a power curve similar to the NA 155 hp motors. It will peak much earlier than the upgraded SC motor.

    The bottom line is that I'm trying to figure out the best combination to get 85+ mph at <8100 rpm. Right now I'm running a 15/20R prop and the stock 83.5 nozzle. I'm at the limiter at 10 psi boost and 77.5 mph.

    Mike

  9. #9
    Quote Originally Posted by JD 1 View Post
    you want the truth or do you want me to sugarcoat it?

    DO you ever sugar coat anyting!

  10. #10
    Moderator The Bandit's Avatar
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    Don't know the dynamics of a turbo setup, but with a Riva ECU, your bests speeds will be seen at 8500-8550 rpm's. I pitched the prop with the 82 ring so I could have some leeway up and down based off the weather.

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