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Thread: Missing RPMS

  1. #1
    Ridin' the Rancocas 04RXP22's Avatar
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    Missing RPMS

    Alright.... Here is my setup.

    15/20r - 4 blade
    Rotax SC wheel
    Stock ECU.
    42# Injectors
    XS IC
    Holes filled
    Bucket Trimmed.
    Front Riva 3" Intake
    R&D Steering nozzle

    that's about all of the important stuff.

    I ran a consistant 76.4-76.6 on several speed passes.

    However, I was only turning 7700-7800 RPMS with about 8.3# of boost.

    How does this sound?
    Where could my RPMS be?


  2. #2

    choices

    (1)add more boost via a bigger wheel in the s/c
    (2) add rear air or front 4 inch
    (3)put less pitch in the prop
    (4) get a bigger nozzle ring for the venturi

  3. #3
    Site Admin Green Hulk's Avatar
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    If you don't have a slipping clutch, over filled oil or a boost leak i would try depitching the trailing edge of the impeller 1.5 mm

  4. #4

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    I HAVE COMPLETE S3 CHARGER FOR SALE TODD

  5. #5
    Quote Originally Posted by Green Hulk View Post
    If you don't have a slipping clutch, over filled oil or a boost leak i would try depitching the trailing edge of the impeller 1.5 mm

    yep forgot about those .....was assuming he had checked those since he was not a noob.

    also remember to make sure the plate holes are filled and all of the silicone on the bottom is nice and tidy.

  6. #6
    Ridin' the Rancocas 04RXP22's Avatar
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    (1)add more boost via a bigger wheel in the s/c
    I just put in the Rotax wheel, go bigger already!
    (2) add rear air or front 4 inch
    This is on my to do list, but it's only good for 50RPM right?
    (3)put less pitch in the prop

    (4) get a bigger nozzle ring for the venturi
    Stock nozzle, I sold the adjustable one.

    If you don't have a slipping clutch
    SC clutch is good
    over filled oil
    Oil level is good - Mid stick
    or a boost leak
    I checked for any boost leak, but I only checked it quickly. I will dig in further and give everything a good check.
    i would try depitching the trailing edge of the impeller 1.5 mm
    1.5mm you say...

    "since he was not a noob."

    also remember to make sure the plate holes are filled and all of the silicone on the bottom is nice and tidy.

    Got that one covered



    Thanks Diggs & Jerry for the replies

  7. #7
    monaroman76's Avatar
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    Quote Originally Posted by 04RXP22 View Post
    Alright.... Here is my setup.

    15/20r - 4 blade
    Rotax SC wheel
    Stock ECU.
    42# Injectors
    XS IC
    Holes filled
    Bucket Trimmed.
    Front Riva 3" Intake
    R&D Steering nozzle

    that's about all of the important stuff.

    I ran a consistant 76.4-76.6 on several speed passes.

    However, I was only turning 7700-7800 RPMS with about 8.3# of boost.

    How does this sound?
    Where could my RPMS be?
    I have a p-x, with riva intake, free flow, R&D grate, so quite similar setups really.. And like you i can only turn out 7700-7800 rpms.. I want to know what is holding my rpms back too..

  8. #8
    JESUS G's Avatar
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    Quote Originally Posted by 04RXP22 View Post
    Alright.... Here is my setup.

    15/20r - 4 blade
    Rotax SC wheel
    Stock ECU.
    42# Injectors
    XS IC
    Holes filled
    Bucket Trimmed.
    Front Riva 3" Intake
    R&D Steering nozzle

    that's about all of the important stuff.

    I ran a consistant 76.4-76.6 on several speed passes.

    However, I was only turning 7700-7800 RPMS with about 8.3# of boost.

    How does this sound?
    Where could my RPMS be?
    With this setup you must have around 8.200 or 8.350RPM, if you don´t have any leak of pressure i think you have check the sleeping momento of washer compressor and too check leaks on the headcylinder and the engine compresion.

    I had the same problem with a customer and the problem was the pistons. The engine had 30% of leak.

  9. #9
    Ridin' the Rancocas 04RXP22's Avatar
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    Quote Originally Posted by JESUSSEADOO View Post
    With this setup you must have around 8.200 or 8.350RPM, .
    With a stock ECU?!?!

  10. #10
    Vern's Avatar
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    Actually your speed is right on ... the fact that your rpms are low would indicate to me that you have too much pitch or too tight of a nozzle. If you are only running the stock nozzle, then your 15/20 might need to be pulled back a bit to get rpms up. But no way is there anything major wrong if you are pulling 76+mph ... just maybe a little too much prop. Good speeds for your setup.

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