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RPM to MPH/MPG correlation

Discussion in 'Gen 2 Prius Fuel Economy' started by ystasino, Dec 29, 2010.

  1. ystasino

    ystasino Active Member

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    I was previously told that, absent a tachometer, I should try to keep my the MPH/MPG ratio at 1.5 to 2.0 for greater efficiency.

    I have now bought a scangauge II and assuming that the Prius sweet spot is at 1800-2200 rpm, that translates to a 1.4-1.6 MPH/MPG. If everybody else's observations agree, maybe we could post this ratio to a sticky thread to help people with their fuel efficiency.

    So I try to keep the rpm at 2000-2100 on the highway and around 1800-1900 rpm in the city. MPG has improved...

    I wonder if your experience regarding the conversion of RPM to MPH/MPG has been similar.
     
    #1 ystasino, Dec 29, 2010
  2. JimboK

    JimboK One owner, low mileage

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    Your findings of the relationship between RPM and the speed/iMPG ratio ("i" for instantaneous, for the sake of newbies who somehow might think tank MPG) largely square with mine which, as you know, I discuss here.

    Meanwhile, also as I discuss there, I have come to believe the optimal RPM is lower than what you're using. Below 40 MPH, if traffic allows, I'm generally in the 1200-1400 range. The ICE still usually is under load (as indicated by injector timing) even at RPM that low. I try to keep highway RPM as low as possible and still maintain appropriate speed; 1600-1800 is routine on level terrain. About the only time I exceed 2000 is accelerating or hill-climbing.

    Also for the newbies: all of this assumes the need for the ICE to be on. High fuel economy driving involves knowing how to get maximum efficiency both when the ICE is on and when it is off; the latter is a different discussion.
     
    #2 JimboK, Dec 29, 2010
  3. ystasino

    ystasino Active Member

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    Ahh, Jim it was your thread, I should have searched more and posted all this there. If the moderators can move it to the original thread you linked it would be great.

    Maybe I missed it, it's 1 am, but have you discussed your highway RPM findings anywhere? I am going on this 575 mi trip from Baltimore, MD to Charleston, SC and I am planning on driving there fast (78 MPH), it's just too long a trip for me to "hypermile" between 60-70, so I doubt I will be able to be at 1600-1800 RPM much.

    What speed sacrifices does your 1600-1800 rule force? What kind of speeds can you maintain at that RPM on level-ish terrain?
     
    #3 ystasino, Dec 30, 2010
  4. JimboK

    JimboK One owner, low mileage

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    I haven't discussed highway RPM much on the forums because I don't do much highway driving. There is some mention on CleanMPG -- the Super Highway Mode discussion and some of Hobbit's threads, in particular.

    You probably can expect around 60 MPH at 1600 on level terrain in warm weather. In fact, 1600 will give you about 60 iMPG at 60 MPH. In the winter, mid-50s maybe. (That could be outright dangerous on your trip down I-95! ;))
     
    #4 JimboK, Dec 31, 2010
  5. tf4624

    tf4624 Active Member

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    Add on tach and or scanguage is your friend
     
    #5 tf4624, Jan 1, 2011
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