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Old 06-04-2013, 12:04 PM   #4351
jsteg
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Quote:
Originally Posted by pxpaulx View Post

No it isn't, you're doing the calculation wrong (or, rather, backwards).

Example:

If the baseline were 100 (or mpg number), then increasing to 125 is a 25% increase.

You are doing the reverse calculation - if the baseline (or mpg number) is 125, then going down 100 is only a 20% decrease.

So you are doing 31 divided by 39, when you should be doing 39 divided by 31.

Haven't posted here in quite awhile but occasionally stop in to read the ridiculousness of this thread - but I can let someone calling their intelligence terrible go unanswered!

Oh and to be relevant to the thread, my take is still (after 17K miles): short trips absolutely kill this car's mpg. And having owned close to a dozen different vehicles (all of which I've averaged close to the epa highway estimates in all-around driving) it is a problem that is completely unique to this car.
All the numbers I quoted were increases so my math is right! At least according to how you're telling me the equation should go....or do YOU have it backwards?
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Last edited by jsteg; 06-05-2013 at 11:49 AM.
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Old 06-04-2013, 05:28 PM   #4352
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Then there's always the argument that comparing variations in MPG isn't really very useful anyway, gallons per mile (or km per litre as us Canucks prefer) are better, when it comes to comparing your bottom line....

http://www.efficient-mileage.com/mpg-illusion.html
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Old 06-04-2013, 06:47 PM   #4353
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Then there's always the argument that comparing variations in MPG isn't really very useful anyway, gallons per mile (or km per litre as us Canucks prefer) are better, when it comes to comparing your bottom line....
Even better is dollars per mile, particularly when comparing vehicles with different fuel requirements. (octane or gas vs diesel, etc)
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Old 06-04-2013, 07:54 PM   #4354
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Even better is dollars per mile, particularly when comparing vehicles with different fuel requirements. (octane or gas vs diesel, etc)
First post that actually makes sense. I think everyone gets caught up in a couple mpg here and there, then converting it to percentages as the numbers are bigger. One issue is as it equates to percentages, you lose accuracy. Averages, means, percentages are all gross calculations. Unless its 0% or 100% its just close. When you are just close, then talking only a few mpg's its like saying you get an extra few feet every 1000 yards. It's barely even noticeable. The reason I'm saying all of this, is everyone is driving differently, different DA ( density altitude) and we all weigh different. Owning drag cars, even 3-4 lbs makes a difference. I bet there is probably even. 50-100 lbs difference in just body weight between several people in here comparing mpg. Then take into account elevation of land, fuel blend, miles on car, etc. My bottom line is I have a spacious enough AWD car that I love and it it gets over 30 mpg as I drive it and it saved me $24X my first week in fuel over my Hemi Ram. So to me its fantastic!!!!
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Old 06-04-2013, 11:35 PM   #4355
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The government is forcing Hyundai to pay up for a small percentage difference.
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Old 06-04-2013, 11:56 PM   #4356
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Originally Posted by hemophilic View Post
The government is forcing Hyundai to pay up for a small percentage difference.
They are also implementing taxes for areas where they have lost tax dollars as a result of too many fuel efficient cars purchasing less fuel. The fuel tax is usually around $0.50 per gallon at the pump retail. So when people talk about fuel taxes, that's what's always brought up. But, that would be assuming that no taxes had to be paid along the way by anyone else. We know that not to be true, as the oil co pays taxes, refineries pay taxes, transport companies pay taxes, and retail sales stations pays taxes twice- sales and income from sales. These taxes pay for roads, law enforcement, etc. So it only seems logical that as efficiency ratings climb, new taxes will need to arise to cover the gap created. I'm all about reducing dependency on oil, being better stewards to the environment, and saving money. But at some point you have to step back and look at the whole picture, it seems silly. The auto makers get penalties for failing to meet standards, then we get it when they all do meet standards.
http://m.usatoday.com/article/news/2110297

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Old 06-05-2013, 07:22 AM   #4357
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The fuel tax is interesting in that it is set in cents per gallon, so it doesn't increase with inflation. Which means, effectively, the gas tax goes down over time. Since people are incredibly price-sensitive with respect to gas, increasing the gas tax to match inflation is political suicide. So they're bound to try to make it up somewhere else, and hybrids and EVs are easy targets.
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Old 06-05-2013, 10:03 AM   #4358
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Originally Posted by G2Spfld View Post
as the oil co pays taxes
That was a good one!
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Old 06-05-2013, 07:03 PM   #4359
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Just filled up. 408 miles / 13.033 = 31.31 Finally I am getting slightly over 30mpg w/A/C on sometimes. Not once during the colder months. Winter MPG's for these cars suck.
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Old 06-05-2013, 10:23 PM   #4360
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Originally Posted by vwgti123 View Post
Just filled up. 408 miles / 13.033 = 31.31 Finally I am getting slightly over 30mpg w/A/C on sometimes. Not once during the colder months. Winter MPG's for these cars suck.
Welcome to the dark side lol
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Old 06-06-2013, 07:47 AM   #4361
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Originally Posted by vwgti123 View Post
Just filled up. 408 miles / 13.033 = 31.31 Finally I am getting slightly over 30mpg w/A/C on sometimes. Not once during the colder months. Winter MPG's for these cars suck.
And every other car
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Old 06-06-2013, 08:30 AM   #4362
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Just filled up the other day, filled up 10 gallons and the average was 33mpg on the display, so probably a little lower, around 31.5mpg. Not bad considering I had to run the A/C constantly after having my windows tinted
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Old 06-06-2013, 09:20 AM   #4363
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I filled up on 6/4 347 miles, 10.2 gallons, I'm happy, seems to be getting better as I approach 10K.
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Old 06-06-2013, 07:05 PM   #4364
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And every other car
Don't want to start another debate.. but this car more so than many others. I hope we can agree on that.
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Old 06-06-2013, 07:48 PM   #4365
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Don't want to start another debate.. but this car more so than many others. I hope we can agree on that.
It's more the underpowered smaller motor fuel efficiency type cars affected really. These cars, like other similar cars, rely heavily on maximizing the little HP they have. When the computer is reading the TPS at higher percentages, it has to automatically adjust injectors. When the fuel blends are winter, lower octane, more E85 ( for cars not tuned for E85) we tend to use more petal, or the cruise uses more petal to compensate, thus the higher TPS readings. E85 tuned cars will automatically have much higher injector pulses and widths. It's kinda the same affect the A/C compressor has on power and MPG ( albeit A/C is more of a drag). Now you take a larger engine, and its not using its HP potential most of the time. The A/C has less of an affect on it, and is less noticeable when A/C is on, just as its less noticeable when using winter blend fuel. Before anyone attacks me on this, I have a few cars with Autronic and AEM ECU's. I understand tuning fairly well. This is my take on your point, and why it's not just a Subaru impreza problem.

Last edited by G2Spfld; 06-06-2013 at 08:38 PM.
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Old 06-07-2013, 12:50 AM   #4366
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Originally Posted by G2Spfld View Post
It's more the underpowered smaller motor fuel efficiency type cars affected really. These cars, like other similar cars, rely heavily on maximizing the little HP they have. When the computer is reading the TPS at higher percentages, it has to automatically adjust injectors. When the fuel blends are winter, lower octane, more E85 ( for cars not tuned for E85) we tend to use more petal, or the cruise uses more petal to compensate, thus the higher TPS readings. E85 tuned cars will automatically have much higher injector pulses and widths. It's kinda the same affect the A/C compressor has on power and MPG ( albeit A/C is more of a drag). Now you take a larger engine, and its not using its HP potential most of the time. The A/C has less of an affect on it, and is less noticeable when A/C is on, just as its less noticeable when using winter blend fuel. Before anyone attacks me on this, I have a few cars with Autronic and AEM ECU's. I understand tuning fairly well. This is my take on your point, and why it's not just a Subaru impreza problem.
No, that's a good point, and one that I'm sure Subaru's 2.0 engineers are aware of. Someone made a conscious decision to maximize efficiency (aka fuel economy) at the meager requirements of the EPA highway test, to the detriment of real world performance. The 2.0 does have some oomph at high rpm's - I've never actually seen it not be able to maintain the speed limit on interstate grades, it's just that sometimes on a hill the instantaneous mpg gauge reads under 10mpg (with the CVT that is).

The thing about a larger engine not needing as much reserve and not dropping as much mpg on e.g. the same grade is that it will "slobber" more under no load and is not getting as good mpg as a baseline.
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Old 06-07-2013, 01:26 AM   #4367
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^^^ pretty much any engine with larger displacement and/or higher cylinder count (even with same displacement) uses more fuel per unit of time even in no/low load conditions.

- Filled the tank yesterday, and average mileage is creeping up ever-so-slightly to a hand calculated 31.98 MPG avg. Will finally reach the 2,500 mi. mark either this weekend or on Kamehameha Day.
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Old 06-07-2013, 02:01 AM   #4368
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To know for sure, we'll need a BSFC map for the FB20. If it's like most engines, the efficiency peak is at low RPMs and 50-70% load. By efficiency, I mean turning gasoline into mechanical energy, which does not translate directly into MPG.

The advantage of the smaller engine is that it can be operated closer to its BSFC sweet spot for longer than a larger engine (without accelerating into illegal speeds). Feathering the throttle is actually not the most efficient way to accelerate.
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Old 06-07-2013, 10:17 PM   #4369
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To know for sure, we'll need a BSFC map for the FB20. If it's like most engines, the efficiency peak is at low RPMs and 50-70% load. By efficiency, I mean turning gasoline into mechanical energy, which does not translate directly into MPG.

The advantage of the smaller engine is that it can be operated closer to its BSFC sweet spot for longer than a larger engine (without accelerating into illegal speeds). Feathering the throttle is actually not the most efficient way to accelerate.
X2- what he said!!
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Old 06-08-2013, 09:44 AM   #4370
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Originally Posted by Commander Keen View Post
To know for sure, we'll need a BSFC map for the FB20. If it's like most engines, the efficiency peak is at low RPMs and 50-70% load. By efficiency, I mean turning gasoline into mechanical energy, which does not translate directly into MPG.

The advantage of the smaller engine is that it can be operated closer to its BSFC sweet spot for longer than a larger engine (without accelerating into illegal speeds). Feathering the throttle is actually not the most efficient way to accelerate.
Using the same energy density of fuel it is linearly proportional to mpg though, isn't it?

The CVT should be able to hold the peak of the BSFC - unfortunately the FB20 doesn't have enough oomph to hold it there at moderate speeds, which is a problem with the "mpg" statistic as well - Like I said, I can get over 50 mpg in my Impreza. Unfortunately I'm making well under minimum wage for the extra time. Some people can't put that 2 + 2 together...
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Old 06-08-2013, 10:32 AM   #4371
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Originally Posted by stevehnm View Post

Using the same energy density of fuel it is linearly proportional to mpg though, isn't it?

The CVT should be able to hold the peak of the BSFC - unfortunately the FB20 doesn't have enough oomph to hold it there at moderate speeds, which is a problem with the "mpg" statistic as well - Like I said, I can get over 50 mpg in my Impreza. Unfortunately I'm making well under minimum wage for the extra time. Some people can't put that 2 + 2 together...
This is the whole issue I had from start with these micro engines. I can get 38 mpg in my corvette driving on cruise on highway at 68 mph with 65 limit. It's an almost 500 HP v8. It does less in town, low 20's down to about 12 mpg
Could this FB20 AWD do better? Yes! I want, if not more power at least quicker revs. I think the torque curve needs work, CVT needs work too. I doubt anyone on here will disagree too much with that, however its not bad. It's a reasonably priced car with space, ok handling, great AWD system, and pretty dang good mpg. It's probably the best in space and AWD categories, but does all of it better than anyone else in same price range I believe. I think people's issue lies in the fact we understand your POV on the topic, but its less of an issue for us that its 2-6 mpg off being able to do what some other unlike car can do. No matter how someone classifies it.
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Old 06-08-2013, 10:41 AM   #4372
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It will never be as good as an old corolla, I guess we are all just stuck with it...

LOL
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Old 06-08-2013, 10:57 AM   #4373
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That's OK, I'll just drive my old corolla and drop the whole argument........ (Hint Hint)
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Old 06-08-2013, 11:49 AM   #4374
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Using the same energy density of fuel it is linearly proportional to mpg though, isn't it?
No... BSFC tells us how much fuel is needed to generate a unit of power over time (Kwh / horsepower-hour). It's likely that the FB20 can make 30 HP more efficiently (Kwh/gal) than 20 HP. Say that 20 HP produces a 55 MPH cruise on level ground, and 30 HP at 70 MPH. While the fuel->power conversion might be more efficient at 30 HP, the power->distance conversion falls off at a faster rate due to drag at the higher speed, so MPG as a whole decreases. BSFC is just one link in the chain.

Quote:
The CVT should be able to hold the peak of the BSFC - unfortunately the FB20 doesn't have enough oomph to hold it there at moderate speeds, which is a problem with the "mpg" statistic as well - Like I said, I can get over 50 mpg in my Impreza. Unfortunately I'm making well under minimum wage for the extra time. Some people can't put that 2 + 2 together...
The CVT can choose a point to follow on a curve within that BSFC map based on power demand. For example, to run at 2500 RPM and 40% throttle or 3000 RPM at 30% throttle, but how much power you demand, and the speed you choose to travel is not within its control. Say the BSFC peak is 50 HP @ 2400 RPM and 60% load. The CVT could only hold that for as long as you had a use for 50 HP, and ratios allowed.

Quote:
This is the whole issue I had from start with these micro engines. I can get 38 mpg in my corvette driving on cruise on highway at 68 mph with 65 limit. It's an almost 500 HP v8. It does less in town, low 20's down to about 12 mpg
I would guess that between aerodynamics and drivetrain, it takes more energy to push an Impreza 68 MPH than a Corvette. Also, the V8 probably requires premium fuel, which the engine can extract more energy from. The Impreza could use a taller top gear, at least in the 5MT.
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Old 06-08-2013, 01:18 PM   #4375
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I agree with your analysis with regards to the Vette, if it were a 4- door wagon with AWD, it would look a little more like CTS-V milage. I think Steve's argument boils down to the fact the CVT doesn't exceed the mpg ratings like other autos supposedly do. I'm not in the auto industry, but when my clients give me a SOW ( scope of work) and a budget of X, I do not exceed the SOW with a budget of 2X. I try to maximize the budget to give him the best I can within and meeting his SOW.
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