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  1. #1

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    rr supercharger impeller question

    Ok i have an 05 rxp completely stock and want to install the rotax racing supercharger impeller as my first mod. I did a search and it seems like the general idea is that you do not need the 42# injectors if you are not going to run an external intercooler.

    But up here in montana we ride in some cold weather. The coldest probly being 45 air and water and the hottest being 70 water and 100 air but most of the riding would be around the 70's (but i would have a few months of 60 air 50 water before this). So if i stayed with the stock injectors would i still be ok and not run too lean in these cooler temps? or should i just install the 42's?


  2. #2
    Will work on YOUR ski for FREE! GeoRXT's Avatar
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    I think you dont need them, because the external intercooler flows a lot more air than the stock one and that would be why you need more fuel in the mixture....

    Am I correct?

    Give it a few minutes and a pro will answer with 100% accuracy.

  3. #3
    Site Admin Green Hulk's Avatar
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    Stock injectors will be fine.

  4. #4

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    so it sounds like it is more of an air flow issue that temperature. So i should be fine to run it with stock injectors even in cold tems. Would adding a 4 inch intake along with the cooler temps affect the afr enough to require the 42's. Also i am only running 7600 rpms even in the cool temps( elevation seems to be the culprit here) so would this mod maybey get my rpms to normal range?

  5. #5
    Site Admin Green Hulk's Avatar
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    You will be fine with the stock injectors. If you add an external intercooler you will want the 42# injectors.

    More boost should bring your RPM's up some.

  6. #6
    Will work on YOUR ski for FREE! GeoRXT's Avatar
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    Could he pitch the prop for higher rpms Jerry?

  7. #7
    Moderator Insanediego Joe's Avatar
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    There are 5 boats here in california running the RR wheel with external intercooler 4" friebe intake. Been running this way for months trouble free. I am not saying it is safe to do this just letting you know what I have been told.

  8. #8
    GTXX's Avatar
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    Quote Originally Posted by Insanediego-RXP View Post
    There are 5 boats here in california running the RR wheel with external intercooler 4" friebe intake. Been running this way for months trouble free. I am not saying it is safe to do this just letting you know what I have been told.
    I've been told the same thing, but that it only safe as long as the water temp is above 65 and the air is warm as well. With this combo in cold water the A/F ratio runs up into the high 12's which is risky.

  9. #9
    sleeplessnMS's Avatar
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    Got 2 guys down here in south MS ran RR wheel, external IC,RRECU with stock injectors all summer.... BUT its hot like 88-90 degree water and 90-110 heat index... That reminds me~DAMM IT WAS HOT AT MBII !!!!!! Jerry ya gonna cool it off a bit b/f we come this yr? I'll take 60 degree wATER say 75-80 air temp....

  10. #10
    shhr's Avatar
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    This may help I will update my numbers again with the new mods

    http://greenhulk.net/forums/showthread.php?t=6044

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