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Thread: An interesting observation on fuel economy

  1. #51
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    Quote Originally Posted by Daox View Post
    Unfortunately, its not super easy to explain as a whole because there are so many factors that effect fuel economy, but I shall attempt to explain how understanding BSFC maps can help.

    The BSFC map show how efficient an engine (and just the engine, not the transmission, or anything else) runs under different loads and RPMs. The vertical axis on the map is torque output which can be related back to the throttle pedal. The more you press the gas pedal the farther up on the map you go. The bold line across the top is the maximum torque output of the engine. The horizontal axis is rpm which I'm sure you're familiar with. So, as you can see in general, more throttle means your engine is actually running more efficiently. This explains why smaller engines get better fuel economy than larger engines. For example, lets say your engine needs to put out 10 horsepower to go 50 mph. A smaller engine is going to have to be loaded more than a larger engine, so the throttle is open farther and thus it operates farther up on the map than a larger engine would.

    Since we don't have a BSFC chart for the Mirage engine's we have to make some assumptions. So, again in general, medium rpm and higher engine load is where an engine runs most efficiently. You can fairly easily accelerate at medium rpm and high load with the help of a scangauge or other OBDII tool. However, once you get up to speed we run into a problem. The area on the map where the engine rust most efficiently is nearly always MUCH more power than is needed for cruising down the road at a given speed. So, you let off the gas pedal... which drops your efficiency. This explains why pulse and glide works. Pulse and glide drivers only operate their engine at peak efficiency to accelerate, then they coast with the engine ON using a minimal amount of gas or they turn the engine off completely. After they coast down a bit, they pulse back up to speed at optimal efficiency. This also explains why taller gearing increases fuel economy as well. The taller your gearing, the more load it puts on the engine, so you move up on the chart.

    Beyond that, the BSFC chart doesn't give a ton of information. But, of course there are still tons of other factors that effect fuel mileage though. For example, the speed of your vehicle is a big factor. The faster you go, the more power it takes to push your car through the air. These are topics for another post though.

    So, I hope that helps some. It is a bit of a confusing subject.
    thanks for taking your time writing this down . One question. pulse and glide, will it mess up your clutch pedal? If I use this technique, does it mean I need to lets say accelerate to 90 kph then coast to 80 and repeat? thanks. Hvae a nice day...


        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage Intense 1.2 manual: 47.9 mpg (US) ... 20.4 km/L ... 4.9 L/100 km ... 57.6 mpg (Imp)


  2. #52
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    Quote Originally Posted by MetroMPG View Post
    Yeah, ability to ecodrive without affecting other drivers depends a lot on local driving "culture".

    I'm really lucky I happen to live in a very laid-back, little city (also, lots of seniors). It's regularly on the lists of "safest" cities in my province, and I've rarely ever seen truly aggressive or rage-y driving here.

    Lots of texting at traffic lights and while moving, unfortunately.
    We took a trip last fall through your hack of the woods last labor day to Montreal via Woolf island, Kingston along st Lawrence River. Very nice and those houses on the islands looked really expensive... not that I would like to be there in the winter months, but it is probably not as bad as upstate NY and doesn't get as much snow.

    Montreal drivers were bad but mostly non-attentive not aggressive and too many potholes.
    Last edited by cyclopathic; 05-20-2016 at 08:38 AM.

        __________________________________________

        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)


  3. #53
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    Quote Originally Posted by Cleartec View Post
    thanks for taking your time writing this down . One question. pulse and glide, will it mess up your clutch pedal? If I use this technique, does it mean I need to lets say accelerate to 90 kph then coast to 80 and repeat? thanks. Hvae a nice day...
    Pulse and glide will wear your clutch out a bit faster as you are engaging and disengaging it more often. The wear from my experience is minimal though. I've never had to replace a clutch on a car I own. It won't effect the clutch pedal.

    Pulsing to 90 kph and coasting to 80 is about the minimum speed difference I'd consider. Going from 90 to 85 is really just not worth it IMO. The gliding time is too short and you'll be pulsing and gliding so often it'll get annoying quickly. The longer the glide the better just so you have to do it less often. So, depending on traffic I'll glide down more or less, or not at all in heavy traffic. I also like to use hills to extend my pulsing and gliding. I pulse up them and glide down them.
    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar, Upper grill block

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        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 47.2 mpg (US) ... 20.1 km/L ... 5.0 L/100 km ... 56.7 mpg (Imp)


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  5. #54
    Quote Originally Posted by cyclopathic View Post
    We took a trip last fall through your hack of the woods last labor day to Montreal via Woolf island, Kingston along st Lawrence River.
    You drove on the 1000 Islands Parkway? It's a beautiful drive. I always take that road instead of the freeway when I'm going that direction.

    Montreal drivers were bad but mostly non-attentive not aggressive
    If you think Montreal drivers are "not aggressive" you would say our local drivers are "almost comatose" by comparison.

        __________________________________________

        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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    Quote Originally Posted by MetroMPG View Post
    You drove on the 1000 Islands Parkway? It's a beautiful drive. I always take that road instead of the freeway when I'm going that direction.
    Yes it was very picturesque (not that I'd wanna be there in winter ). Made me wanna come back on motorcycle one day.

    Quote Originally Posted by MetroMPG View Post
    If you think Montreal drivers are "not aggressive" you would say our local drivers are "almost comatose" by comparison.
    Yeah Montreal wasn't bad by US standards but too many potholes for my liking. Drivers were polite and a little bit slow on uptake. If you drive like that in NYC you'd be decimated people would stump all over you.

    I've driven in many metropolitan areas around US, and IMHO DC drivers are the worse. You have a really bad mix of people who are way too aggressive and people who don't know how to drive. At least in New York people who shouldn't be driving taking subway; the people who left on the road are mostly good drivers, so you'd be alright as long as you keep up and don't impede them.


        __________________________________________

        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)


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