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Thread: Gas mileage / MPG achievements (with optional MPG computer pics)

  1. #311
    Still Plays With Cars Loren's Avatar
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    Quote Originally Posted by 7milesout View Post
    The takeaway is that engine efficiency and driving efficiency (of a whole system) are not necessarily mutually related.
    Oh, for sure. The ENGINE is most efficient somewhere in the range of its torque peak. It's making the most rotational force with the amount of fuel that it's burning. That doesn't account for what gear your in, how fast you're driving, road conditions, aerodynamics, etc. There are absolutely other variables to be considered.

    Note that I was talking about accelerating.

    If you're CRUISING, you're going to get the best economy in the highest gear you can be in, regardless of RPM (assuming RPM isn't so low that the engine is lugging). This gives you the best gearing advantage and multiplies the efficiency of the engine.

    But, hypermilers rarely cruise. Your best "record setting" MPG isn't going to come from just cruising down the road at a constant speed. It's going to come from accelerating up to a target speed, and coasting down to a lower target speed, working with the terrain where possible, and continuing to do that.

    If you just want 45 mpg, then cruise and keep your speed under 65. If you want to see 60 or 70 mpg... it won't happen that way.

    There are some hypermiling techniques that seem counterintuitive at first, but they work.

    So, to use your example, if the target is 50 mph...

    You put an experienced hypermiler in Car A, and tell him to get somewhere that's 50 miles away in one hour. He's not going to drive 50 mph. He's going to accelerate up to 60-62, and then neutral coast down to 42-45, and then accelerate back up to 60. Lather, rinse, repeat. And if he does it right (working with the terrain, effectively managing traffic and stops), he's going to get BETTER fuel economy than the driver in Car B who set the cruise control at 50.

    He'll be accelerating in the torque peak range of the engine (even in 5th at those speeds), thus getting the most out of the fuel. And he'll be using gravity and momentum to carry the car between "pulses" of acceleration.

    Car B will net some pretty good MPG in a Mirage at 50 mph constant. But, Car A will do better.

    Find yourself a nice back road and try it!


    Simplify and add lightness.

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  3. #312
    I'll never be able to compare with other's crazy high short drive hypermiling numbers. I'm just happy to get over 40mpg per tank without thinking much about it. My last tank averaged 44.4mpg hand calculated, good enough for me. I was on my way to a new best and then we got a foot of snow and it cooled off. Thanks covid!
    Mirage videos:

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage SE wussie cvt edition. 1.2 automatic: 37.7 mpg (US) ... 16.0 km/L ... 6.2 L/100 km ... 45.3 mpg (Imp)


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    davidricardo86 (11-14-2020),Loren (11-12-2020),MetroMPG (11-12-2020)

  5. #313
    Still Plays With Cars Loren's Avatar
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    I just wish I lived somewhere that was a bit less "big city". This is the hardest environment to get decent gas mileage in.
    Simplify and add lightness.

  6. #314
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    Quote Originally Posted by Loren View Post
    Oh, for sure. The ENGINE is most efficient somewhere in the range of its torque peak. It's making the most rotational force with the amount of fuel that it's burning. That doesn't account for what gear your in, how fast you're driving, road conditions, aerodynamics, etc. There are absolutely other variables to be considered.

    Note that I was talking about accelerating.

    If you're CRUISING, you're going to get the best economy in the highest gear you can be in, regardless of RPM (assuming RPM isn't so low that the engine is lugging). This gives you the best gearing advantage and multiplies the efficiency of the engine.

    But, hypermilers rarely cruise. Your best "record setting" MPG isn't going to come from just cruising down the road at a constant speed. It's going to come from accelerating up to a target speed, and coasting down to a lower target speed, working with the terrain where possible, and continuing to do that.

    If you just want 45 mpg, then cruise and keep your speed under 65. If you want to see 60 or 70 mpg... it won't happen that way.

    There are some hypermiling techniques that seem counterintuitive at first, but they work.

    So, to use your example, if the target is 50 mph...

    You put an experienced hypermiler in Car A, and tell him to get somewhere that's 50 miles away in one hour. He's not going to drive 50 mph. He's going to accelerate up to 60-62, and then neutral coast down to 42-45, and then accelerate back up to 60. Lather, rinse, repeat. And if he does it right (working with the terrain, effectively managing traffic and stops), he's going to get BETTER fuel economy than the driver in Car B who set the cruise control at 50.

    He'll be accelerating in the torque peak range of the engine (even in 5th at those speeds), thus getting the most out of the fuel. And he'll be using gravity and momentum to carry the car between "pulses" of acceleration.

    Car B will net some pretty good MPG in a Mirage at 50 mph constant. But, Car A will do better.

    Find yourself a nice back road and try it!
    Loren - I know all about the P&G. I know a lot about hypermiling in general. I worked in automotive in engineering for a looong time. Myself and other actual automotive guys (there are plenty of non-automotive people working in automotive fields) talked about cars all day long every day. And it was accepted due to the field we worked in.

    That said, I agree with you about the P&G. But it is a hella annoying way to drive. And the world behind a hypermiler is going to be hella annoyed as well. I just drive my car like a car was intended to be driven, and mostly go with the flow, because those that don't, I too find annoying.

    As for the acceleration thing and trying to accelerate at the engine's most efficient condition. Acceleration can be broken down into finite elements. Like analyzing the stresses in a component or assembly (FEA - finite element analysis). When determining the system fuel efficiency via finite elements, it can be determined that overall system mpg is higher at slower, lower rpm accelerating.

    Consider this if you can imagine it (I'm betting you can, sounds like you have a V8 for a brain - motorhead). The speed differential at every 0.001 seconds of an acceleration event turns out to be ~ 0 acceleration. And thus since ~0 acceleration, it more closely resembles steady state cruising. Which condition is more efficient at steady state cruising (at each finite acceleration element)? 10% throttle at 2,500 rpm? Or 85% throttle at 4,250 rpm?


    7milesout

        __________________________________________

        click to view fuel log View my fuel log 2020 Mirage ES 1.2 manual: 42.4 mpg (US) ... 18.0 km/L ... 5.6 L/100 km ... 50.9 mpg (Imp)


  7. #315
    To confuse matters more: there's a difference between best efficiency (most power per unit of fuel burned) and best fuel economy.

    10% throttle at 2,500 rpm = lower fuel consumption

    vs

    85% throttle at 4,250 rpm = higher efficiency

    Assuming constant speed.

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 63.2 mpg (US) ... 26.9 km/L ... 3.7 L/100 km ... 75.9 mpg (Imp)


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  9. #316
    I assume calculated engine load has already been mentioned too?

    Are we all talking about the same thing? When I compare two cars to try to find out which one is more efficient I'd only care about which one uses less fuel to get from point a to point b while taking the same time to get there. If one drives at 4000rpm and the other at 2500 rpm I would assume the 2500 would use less fuel unless it was lugging badly and held to the floor the entire time to keep it running.
    Mirage videos:

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage SE wussie cvt edition. 1.2 automatic: 37.7 mpg (US) ... 16.0 km/L ... 6.2 L/100 km ... 45.3 mpg (Imp)


  10. #317
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    Quote Originally Posted by MetroMPG View Post
    To confuse matters more: there's a difference between best efficiency (most power per unit of fuel burned) and best fuel economy.

    10% throttle at 2,500 rpm = lower fuel consumption

    vs

    85% throttle at 4,250 rpm = higher efficiency

    Assuming constant speed.
    MetroMPG - That is what I'm (trying) to discuss. But I stink at explaining.

        __________________________________________

        click to view fuel log View my fuel log 2020 Mirage ES 1.2 manual: 42.4 mpg (US) ... 18.0 km/L ... 5.6 L/100 km ... 50.9 mpg (Imp)


  11. #318
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    Quote Originally Posted by Fummins View Post
    I assume calculated engine load has already been mentioned too?

    Are we all talking about the same thing? When I compare two cars to try to find out which one is more efficient I'd only care about which one uses less fuel to get from point a to point b while taking the same time to get there. If one drives at 4000rpm and the other at 2500 rpm I would assume the 2500 would use less fuel unless it was lugging badly and held to the floor the entire time to keep it running.
    I think we all mostly agree. My basic point I try to make is that maximum engine efficiency does not necessarily equate to maximum mpg.

        __________________________________________

        click to view fuel log View my fuel log 2020 Mirage ES 1.2 manual: 42.4 mpg (US) ... 18.0 km/L ... 5.6 L/100 km ... 50.9 mpg (Imp)


  12. #319
    I agree with that.
    Mirage videos:

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage SE wussie cvt edition. 1.2 automatic: 37.7 mpg (US) ... 16.0 km/L ... 6.2 L/100 km ... 45.3 mpg (Imp)


  13. #320
    Still Plays With Cars Loren's Avatar
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    I think we're all agreeing from different angles.


    Simplify and add lightness.

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