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Thread: row-your-boat owners: what RPMs do you shift?

  1. #21
    Carmageddon m4v3r1ck's Avatar
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    Quote Originally Posted by MetroMPG View Post
    I'd say Nay to the shift light.

    If you want to save fuel, get an instant fuel economy display (better) or a vacuum gauge (cheaper). (It's too bad the car didn't come with the instant display - the Versa Note has both instant & average displays.)

    When to shift depends on so many variables, a simple light isn't good enough. EG if going for best economy, there will be plenty of times you'll moving along under light engine load beneath the shift light's 3k (or whatever) setting and you COULD upshift, but the light won't come on to remind you.
    I still say light on the throttle and make sure you don't switch at higher than 2k. Oh let the car rolls on the highest gear possible, 0L/100km I've tried that


        __________________________________________

        click to view fuel log View my fuel log 2013 Mirage 1.0 manual: 47.5 mpg (US) ... 20.2 km/L ... 5.0 L/100 km ... 57.0 mpg (Imp)


  2. #22
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    Thought I'd resurrect this topic based on a terribly unscientific test I did yesterday...

    I saw a tip on Fuelly.com about shifting at a higher RPM can (possibly) get you higher MPG. The thought is that when you allow your engine to get up to where peak torque is, the engine operates at peak efficiency. Or something like that. I don't even begin to qualify as anywhere near an expert on these things.

    I usually shift at around a little over 2k RPM, and get around 44ish mpg, maybe 2-3mpg better on the highway. My thinking has always been, the lower the RPMs, the more efficient. I don't lug the engine, but I'll typically be in 4th gear at 25-30mph in my neighborhood.

    So yesterday, I decide to put it to the test. Didn't press on the accelerator any harder than usual, but I did shift around 3500 RPM. Otherwise, I drove in regular traffic, exactly like I normally do. 12 miles roundtrip to church at back home, mixed highway/city, and then that afternoon, 40 miles roundtrip to my inlaws. 25mph areas, I drove in 3rd gear at around 2k RPMs. Used cruise control. Ended the day with the MPG reading at 50.6mpg.

    Obviously it's a very unscientific test. But is there potential validity in this? It certainly was more fun to drive, shifting at a higher RPM, and if I can get better MPG out of it too, all the better.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 44.1 mpg (US) ... 18.7 km/L ... 5.3 L/100 km ... 52.9 mpg (Imp)


  3. #23
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    Quote Originally Posted by MetroMPG View Post
    I'd say Nay to the shift light.

    If you want to save fuel, get an instant fuel economy display (better) or a vacuum gauge (cheaper). (It's too bad the car didn't come with the instant display - the Versa Note has both instant & average displays.)
    ELM327 adapter $5 and Torque OBD Android app (free or pro $5), and the good phone mount.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 46.4 mpg (US) ... 19.7 km/L ... 5.1 L/100 km ... 55.7 mpg (Imp)


  4. #24
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    I do 4k normally, but I do enjoy bring it up to 6k now and again, I average 45 mpg with a full 2 inch exhaust and with my custom made 2.5 inch intake.

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage es 1.2 manual: 43.7 mpg (US) ... 18.6 km/L ... 5.4 L/100 km ... 52.5 mpg (Imp)


  5. #25
    Administrator MetroMPG's Avatar
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    Quote Originally Posted by wellswebdesign View Post
    But is there potential validity in this?
    Yes. But implemented wrong it will get you worse MPG.

    For best MPG, you should always cruise in the highest gear possible for the conditions.

    But for acceleration...

    If you want to understand it thoroughly, read up on BSFC (brake specific fuel consumption) and digest some BSFC maps/graphs. They show that engines produce the most power PER UNIT OF FUEL BURNED in a relatively narrow RPM range, roughly 2000-3000 RPM for small-ish engines, at high load (throttle position) but not max load where you get fuel enrichment. So, the most work produced per unit of fuel = more efficient.

    So, yes, it's definitely arguable that accelerating at moderate to high load while shifting at low to moderate RPM is more efficient than feather-footing and short-shifting.

    But what these articles never say is the most important thing: what happens AFTER you burn that fuel to get up to speed? If you blast off from a stop and then immediately get on the brakes, your MPG is going to be toast. The feather-footing "less efficient BSFC zone" driver is going to do better.

    The most efficient and extreme way to benefit from making use of the best BSFC load+RPM combination is the "pulse & glide" or "burn & coast" driving technique. Accelerate, then coast in neutral with the engine off. Rinse & repeat. It's how those ultra-mileage cars operate to get insane numbers.

    It's also why CVT's are theoretically more efficient than other transmission styles: they can hold the engine RPM at the best RPM for a given load.

    But in my opinion, people worry too much about acceleration technique. The typical driver really wastes more gas with the brake pedal than the gas pedal by needlessly rushing into predictable slowdowns & stops.

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage SE 1.2 manual: 58.7 mpg (US) ... 24.9 km/L ... 4.0 L/100 km ... 70.4 mpg (Imp)


  6. #26
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    Anyone connected OBDII scanner and looked how drive-by-wire works on Mirage?

    I've looked how it is done on Prius C, and for the most part ECU runs ICE at low RPM and 20-45% open throttle, which produces low manifold vacuum (-1..5psi). This is done to reduce pumping and friction loss. I wonder if Mirage implements similar strategy. The point is you can't make assumption accelerator position = throttle position on drive-by-wire systems.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 46.4 mpg (US) ... 19.7 km/L ... 5.1 L/100 km ... 55.7 mpg (Imp)


  7. #27
    Senior Member Ares's Avatar
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    Quote Originally Posted by cyclopathic View Post
    Anyone connected OBDII scanner and looked how drive-by-wire works on Mirage?

    I've looked how it is done on Prius C, and for the most part ECU runs ICE at low RPM and 20-45% open throttle, which produces low manifold vacuum (-1..5psi). This is done to reduce pumping and friction loss. I wonder if Mirage implements similar strategy. The point is you can't make assumption accelerator position = throttle position on drive-by-wire systems.
    Good thought. I have a couple of extra phones that would work as a fixed/mounted for this.

    I still shift around 3k-ish.

  8. #28
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    My Eco shift method for this car is get the car rolling, immediately shift to second, 2k shift to 3rd, 3k shift to 5th. 50+ mpg easy.


    That said, I hoon the piss out of this car and live with 44...
    Resident Tire Engineer

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 44.4 mpg (US) ... 18.9 km/L ... 5.3 L/100 km ... 53.3 mpg (Imp)


  9. #29
    Senior Member Ares's Avatar
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    Yah. With the way I drive, and my wide/heavy 15" wheels, the computer grades me at 35ish mpg.

    EDIT:
    I'm going to san antonio this weekend and was going to put the stock eco wheels on... Until I remembered that one of them has a puncture... sigh.

    Might be better to have my 195s anyway as there is an 80% chance of rain friday.

  10. #30
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    below 2000tr/min when i want a really good mpg.
    up to 4000tr/min when i this it's an EVO lol, at least it's a mitsubishi


        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage DE 1.2 manual: 44.8 mpg (US) ... 19.1 km/L ... 5.2 L/100 km ... 53.8 mpg (Imp)


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