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  1. #1

    Join Date
    Jan 2006
    Puerto Rico

    stock 38lbs/hrs vs RR 42lbs/hrs injectors fuel consuption??

    I am ready to test the new RR SC imp with the high flow 42's injectors, but before i want to know how much this new set-up would hurt my ski fuel consuption since i do a lot of long distand rides with my buddies and is almost imposible to find "good gas" premium (91/93) octane in our local marinas, thanks


  2. #2
    Jarrett's Avatar
    Join Date
    Apr 2005
    Waxahachie, TX
    I dont know, but I am interested as well.

  3. #3
    HOSS's Avatar
    Join Date
    Aug 2005
    Kenner, LA
    You don`t build for power with fuel savings in mind. But to answer your question, if you keep rpm`s down, then fuel consumption should be very comparitive.

  4. #4

    Join Date
    May 2005
    Fredericksburg, VA
    In theory you will use 11% more fuel at all times. The computer has no way of knowing you have switched to 42's and will allways be injecting what it thinks is the right amount for 38's.

  5. #5
    Here is the numbers for a stock RXP. I'm sure a RXT would be slightly worse. I found it at
    Now if someone could just test with the RR wheel and ECU at 50% throttle... Stock you should get a little less than 3 hours. So if someone could just go 50% for at least 3 hours we would have some good data.

    The magic number is 25% throttle which is 35.9mph stock and gives 183 miles a tank(5hours riding)!!! At 75% seems your gas consumption goes to crap.
    100% throttle and you can just go 54 miles which is under an hour.

    Throttle MPH Knots Total GPH MPG NMPG Range NM Range
    10% 5.0 4.3 .9 5.56 4.83 80 69
    25% 35.9 31.2 2.8 12.82 11.15 183 160
    50% 47.8 41.5 5.0 9.55 8.3 137 119
    75% 60.7 52.7 15.5 3.91 3.4 56 49
    100% 65.5 56.9 17.4 3.76 3.27 54 47

    Performance Chart

    Test Conditions

    Time To Plane: 1.2 secs
    0 to 30: 2.2 secs
    Test Power : 1x215hp Rotax Waterjet
    Transmission: Direct Drive
    Ratio: 1.0:1
    Props: Stainless Steel Impeller
    Load: 1 person; 1/2 fuel;0 water; 0 gear;
    Climate: 80.7 degrees; 79% RH; 4.2mph wind; minimal chop; salt water

    Speeds measured with Stalker ProSports radar gun. Fuel consumption (gallons per hour) measured with Floscan digital fuel-flow meter on gas inboards, sterndrives, and outboards, TechMate electronic scan tool on gas EFI inboards, Caterpillar digital fuel-flow meter on diesel engines, or permanently installed fuel-monitoring equipment. Range is based on 90% of published fuel capacity. Sound levels determined using Radio Shack digital decibel meter on A scale. 68 dbA is the level of normal conversation.

  6. #6
    Quote Originally Posted by bankyf
    In theory you will use 11% more fuel at all times. The computer has no way of knowing you have switched to 42's and will allways be injecting what it thinks is the right amount for 38's.
    That makes since!
    I bet Jerry will be able to stay WOT for like 30 minutes with 50lbs and all the injectors

  7. #7

    Join Date
    May 2005
    Fredericksburg, VA
    Does anyone know how fuel pressure is controlled on this motor? If we could bump the fuel pressure a little we could accomplish the same thing for possibly less money.

  8. #8

    Join Date
    Jul 2005
    Lake Dunlap, Texas
    With injectors---how come no one cares about pulse width --thats the most important spec--increase the pulse width--you increase the fuel--with the same injector.

  9. #9
    suck my wake's Avatar
    Join Date
    Apr 2006
    Wheaton IL
    Sundance: it seems like most of these guys are not automotive savy. There are alot of basic things to do to make this motor wake up. The previous post about fuel pressure for instance. That can and will add more fuel with the same injectors, we just need to figure out how. Someone will come out with an adjustable fuel pressure reg soon I suppose then we will need another guage

  10. #10
    Ray I'll post some info this weekend. My Rxp averaged 6 miles per gallon during a normal ride with the 38's. I'll know after the weekend how the 42's affect fuel consumption. I would think it would remain about the same. With more hp you will need a larger prop and will spin less rpm to go the same speed. You'll still need the same horsepower to run a given speed as before, I would think.

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