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(Boston Globe)   Fuel economy myths debunked: Even if you keep your windows up, your AC off, lose 50 pounds -- you're going to get the same crappy mileage   (boston.com) divider line 338
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20970 clicks; posted to Main » on 05 Jun 2008 at 1:37 PM (6 years ago)   |  Favorite    |   share:  Share on Twitter share via Email Share on Facebook   more»



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2008-06-05 05:06:16 PM  
voidrunner:

Because you talk like you are a 19 year old punk, who, and you kept comming up with more reasons why you were right, but didn't state until it came convienent for your argument. and this car i have yet to see a pic of, or at least the engine, and tranny


I'm noticing you and impaler's grammar keeps getting worse and worse the more flustered you get. Why does it matter what the facts are? My statement was that slowing down doesn't always net better gas mileage. This is a fact. The details behind it are irrelevant.

Why do you want to see my engine and transmission? It's nothing special. The engine is a 350 bored and stroked to 383 with a SuperRam intake. The transmission is a TH400 changed from a 3 speed to a 6 speed. It looks pretty much stock. There's nothing special or awesome about any of it.
 
2008-06-05 05:07:57 PM  
Animatronik:

Why do you keep claiming to debunk fuel economy myths then saying "my car is a race car, I don't care about fuel economy"? That's...well that's pretty moronic, even for a troll.


Why do I have to have an interest in the subject to debunk it? What if someone claimed Herbert Hoover was a midget? I don't give two shiats about Hoover, but there would be nothing wrong with me debunking that.
 
2008-06-05 05:09:43 PM  
I have allowed Hubby to play with the A/C or Heat to his liking, despite the fact that he NEVER dresses properly for the weather, and he always takes his coat off when he's in the car...been this way for the first fourteen years we've been together. But since my headaches have reached an all time high and can go off at a drop of a hat (i.e. comfort level can be altered...I really do hate that now), I am now in charge of temperature control. We were on our way to KCMO last night, driving in town, and it's 85 degrees, and in the last few days it's been sunny during the day, rainy during the night, and he rolls the windows down. I have long, easily unmanageable hair, and I don't like ponytails much anymore. No way in hell. I told him, "Nope, too much humidity. Turn the air on." He tries to give me the riot act about the MPG's with A/C vs. windows down. "I don't care. Air conditioning is coming on. We're driving a Prius and using at the most THREE drops of gas from Point A to Point B. You'll get over it." There were other mitigating factors as to why I needed the air on...but if you have A/C in your car...why not?

/Owned the Prius for the past 3 years...still love it!
// 40/city 50/hwy...not too shabby
 
2008-06-05 05:13:08 PM  
ThrobblefootSpectre: Please give this example.

Look at my 03:54:55 PM. You need to consider specific fuel consumption as a function of rpm and throttle position. As an example, my Elantra does, in fact, get better mileage, on cruise control, at 67-69 (38 mpg) than 55 (36, just as the EPA claims). It has an instantaneous mpg meter on the dash, I've checked it many times. After 69 mph mileage falls off pretty quickly--down to 30 at 80 mph.

That's the difference between roughly 2200 and 2700 rpm (manual transmission). The torque max of the engine is at 3000. Generally, piston engines will have the lowest specific fuel consumption (fuel per power per time) near the torque max and with a mostly-open throttle.

Aero drag isn't as big a factor as people assume. Pumping air through the engine is. Want to prove it? Drive at seventy. Lift the throttle completely. The car slows down fast, it's trying (and succeeding) to build a vacuum in the intake manifold. Get back up to seventy. Now jam in the clutch as you lift the throttle. The car slows down much more slowly. That's aero braking only. Get back to seventy. Downshift and lift. The car slows down really fast, because it's trying to pump air really fast, and there isn't any.

If you are driving a slushbox, forget it. You are throwing away about 10% fuel mileage pumping hydraulic oil around.

Why is 55 the magic number? What people consider the "average" car? It's because the government tests them at that speed, and the manufacturers try to optimize the tuning and the geartrain to achieve good mileage at that speed because it is a selling point. Not because 55 is some magical number, because it is a regulation (not a law), set by the EPA. Change the rear end or top gear to be 10% higher, and the car will get max mileage at 60 mph. It will get there a little slower, but the little change in aero drag won't cancel the effect of hitting the right rpm and throttle position for minimum specific consumption. The bureaucrats have outperformed as propagandists and beaten the engineers on this one.

It's lbs/hp/hr. Or g/W/s. Where your car minimizes that, that's where it goes farthest on the least fuel.
 
2008-06-05 05:13:16 PM  
Tourney3p0: I'm noticing you and impaler's grammar keeps getting worse and worse the more flustered you get. Why does it matter what the facts are? My statement was that slowing down doesn't always net better gas mileage. This is a fact. The details behind it are irrelevant.

The details are very relevant. Highest gear usually nets the best fuel economy until around the 60 mph mark. That's how you know people that say they get better mph at 80 than 60 are full of shat. It's basic physics.
 
2008-06-05 05:15:55 PM  
impaler:

The details are very relevant. Highest gear usually nets the best fuel economy until around the 60 mph mark.


Okay, automatic transmission. Shifts to 4th gear overdrive precisely at 45. Tell me, is the person going to get better mileage at 44 or 46?

You need to keep in mind that my statement this entire time has been nothing more than "Slowing down doesn't always increase gas mileage." Anything I've said to support that claim has been nothing more than a detail.
 
2008-06-05 05:18:57 PM  
Tourney3p0: Okay, automatic transmission. Shifts to 4th gear overdrive precisely at 45. Tell me, is the person going to get better mileage at 44 or 46?

46

Now the car shifts into hyper-drive at 95. Does the car get better mileage at 46 or 96?

(answer: 46)
 
2008-06-05 05:19:26 PM  
I liked the picture that went along with the pickup tail gate idea. The pickup had a camper shell.

If there is a marginal decrease in drag on a pickup truck when the tail gate is down, it would only apply to open-bed trucks. If you want to decrease the drag, get a cover. I'm sure it'll pay off. Sometime. Hopefully before your truck rusts.
 
2008-06-05 05:22:07 PM  
You know, it was quite valuable to us employees who could be sitting at work and go to a discussion page called "Fuel economy myths debunked", knowing that people would start posting gratuitous cleavage pics. If anyone checked my browser history, or some corporate master list of pages accessed, the title wouldn't create any suspicion.

No more, apparently. The carefree Fark days are gone.
 
2008-06-05 05:26:19 PM  
Taxvictim: You know, it was quite valuable to us employees who could be sitting at work and go to a discussion page called "Fuel economy myths debunked", knowing that people would start posting gratuitous cleavage pics. If anyone checked my browser history, or some corporate master list of pages accessed, the title wouldn't create any suspicion.

No more, apparently. The carefree Fark days are gone.


Not sure what carefree days you're referring to, but if they want to monitor you, images could easily be listed as webpages. So those www.skankyho.com pics you downloaded on the webpage: "how to serve your corporate master," will still be suspicious.
 
2008-06-05 05:30:23 PM  
What, no Honda Civic picture by freezebyte yet?

He's slipping.
 
2008-06-05 05:31:19 PM  
impaler:

46

Now the car shifts into hyper-drive at 95. Does the car get better mileage at 46 or 96?

(answer: 46)


Thank you for conceding my point. Your use of hyperbole was an excellent way of admitting defeat as well.
 
2008-06-05 05:36:57 PM  
Tourney3p0: Thank you for conceding my point. Your use of hyperbole was an excellent way of admitting defeat as well.

Actually since it's 46 and not 96, I win and you lose. Thanks for playing tard.
 
2008-06-05 05:38:11 PM  
impaler:

Actually since it's 46 and not 96, I win and you lose. Thanks for playing tard.


It's also 25 and not 1028. I win now. If I had done this at the very beginning of the thread we both would have saved a lot of trouble.
 
2008-06-05 05:40:05 PM  
Juniper Jupiter: I have allowed Hubby to play with the A/C or Heat to his liking, despite the fact that he NEVER dresses properly for the weather, and he always takes his coat off when he's in the car...been this way for the first fourteen years we've been together. But since my headaches have reached an all time high and can go off at a drop of a hat (i.e. comfort level can be altered...I really do hate that now), I am now in charge of temperature control. We were on our way to KCMO last night, driving in town, and it's 85 degrees, and in the last few days it's been sunny during the day, rainy during the night, and he rolls the windows down. I have long, easily unmanageable hair, and I don't like ponytails much anymore. No way in hell. I told him, "Nope, too much humidity. Turn the air on." He tries to give me the riot act about the MPG's with A/C vs. windows down. "I don't care. Air conditioning is coming on. We're driving a Prius and using at the most THREE drops of gas from Point A to Point B. You'll get over it." There were other mitigating factors as to why I needed the air on...but if you have A/C in your car...why not?

/Owned the Prius for the past 3 years...still love it!
// 40/city 50/hwy...not too shabby


Tell hubby the A/C runs off the electric motor (it does).
IF you are travelling over 40 miles per hour the gas engine is running anyway, thus charging the hybrid battery. The only time the A/C really robs the batteries is under 40. At the end of the day you're still ahead on MPG. And, if you are happy and in good shape he is more likely to get the 'giggity'.


/52mpg with mine.
//I can't wait till the Gen3 comes out....
 
2008-06-05 05:41:39 PM  
pandabear:
Aero drag isn't as big a factor as people assume. Pumping air through the engine is. Want to prove it? Drive at seventy. Lift the throttle completely. The car slows down fast, it's trying (and succeeding) to build a vacuum in the intake manifold. Get back up to seventy. Now jam in the clutch as you lift the throttle. The car slows down much more slowly. That's aero braking only. Get back to seventy. Downshift and lift. The car slows down really fast, because it's trying to pump air really fast, and there isn't any.


Your example is a bit of a non-sequitor as it displays the obvious impact of a closed throttle, but does not address the difference between a 90% and 80% open throttle (and it's not linear) on pumping loss. Typical volumetric efficiency for a modern engine is 80-90%.

Also note that diesels have NO throttle, yet they also get better mileage at low speeds. The aerodynamic losses really are that big relative to the drive train losses (drive train components are moving faster and have higher losses too) at highway speeds.

Road load power is approximately:

Pr = (CR * Mv * g + 1/2 rhoa * Cd * Av * Sv^2) * Sv

CR = coefficient of rolling resistance
Mv = mass of vehicle
g = gravity
rho a = density of air
Cd = drag coefficient
Av = frontal area of vehicle
Sv = vehicle speed
(all metric units)

That's what the engineers say (well, John Heywood at least and he's pretty damn mainstream) based on an awful lot of testing and data.

Not because 55 is some magical number, because it is a regulation (not a law), set by the EPA. Change the rear end or top gear to be 10% higher, and the car will get max mileage at 60 mph. It will get there a little slower, but the little change in aero drag won't cancel the effect of hitting the right rpm and throttle position for minimum specific consumption.

If you "change the rear end" (optimize the entire system to the theoretical maximum) to get the best mileage at 55 mph, it will, by law (of nature) get better mileage than at 60 mph. You can't fight that Sv factor.
 
2008-06-05 06:09:07 PM  
only best advice I can give has to do with smaller engines...

the smaller your engine is on an automatic, the more gas you'll save by popping it out of gear at long lights
 
2008-06-05 06:12:21 PM  
allegedman
"the solution for low gas price... DRILL FOR MORE OIL
We cant drill for oil in these parts because congress said no when we should be increasing our dependance.

DRILL FOR MORE OIL AND BUILD NEW REFINERIES!!!"


OR we could do the intelligent thing and instead of spending money on drilling and building refineries for vehicles that use petrols for fuel as efficiently as using brillo to maintain a fire, we could invest that money into the research and technology to make electrical automotives more efficient and economic.

Actually, no, let's just keep science out of the picture.
 
2008-06-05 06:19:55 PM  
MrSteve007: jvl: impaler: The injectors are turned OFF if the throttle is closed and the car is in gear - so no gas is used and the kinetic energy of the car turns the engine.

Probably not true for most cars. On the cars that I've owned and have done significant work on (and therefore research on) fuel mixture is simply a function of RPM, manifold pressure (or vacuum), air temperature and O2 readings. Throttle position is not considered unless at Wide Open. The computer isn't smart enough to know that you're coasting down a hill. Besides, turning off the injectors could cause a lean mixture, which can be BAD. I doubt that any car manufacturer would want to buy an engine because of a software bug. They'd rather toss in a little extra fuel and be safe.
 
2008-06-05 06:37:49 PM  
Don't forget Kangaroo Boots that let you run 25 mph.

http://www.youtube.com/watch?v=AcWGCvazH8k

/ Starts with bad 80's music
// Not a rick roll
 
2008-06-05 06:39:03 PM  
allegedman
"the solution for low gas price... DRILL FOR MORE OIL
We cant drill for oil in these parts because congress said no when we should be increasing our dependance.

DRILL FOR MORE OIL AND BUILD NEW REFINERIES!!!"


tons0phun

OR we could do the intelligent thing and instead of spending money on drilling and building refineries for vehicles that use petrols for fuel as efficiently as using brillo to maintain a fire, we could invest that money into the research and technology to make electrical automotives more efficient and economic.

Actually, no, let's just keep science out of the picture.


Currently, we use oil as fuel. When the new fuel comes along we will switch. Plenty of "top men" working on it; nothing new yet. Sadly, idiots keep wasting time on solar and wind, which haven't shown much promise. And why keep plugging away at those? "Because there HAS to be something there!" It's too uncomfortable to admit that the hippie fantasy didn't pan out. Nuclear is grand. But nope. "That's scary! Doesn't 'nulcear' mean 'bomb'?"

There's so much money-wasting, wishful thinking and P.C.-induced fear in science that it can hardly claim the moral high ground that most Farkers constantly want to attribute to it. (Where is your science now? Ha, ha!)

Meanwhile, we're dependent on primitive-minded Saudis and our economy is hurting, while we have plentiful oil under our own land. That's a stupid culture starving to death at a feast.

Refusing to drill for more oil while we wait for your hot new science is like saying that you're not going to date anyone because you're waiting for a supermodel to call you.
 
2008-06-05 06:39:21 PM  
Surpheon: If you "change the rear end" (optimize the entire system to the theoretical maximum) to get the best mileage at 55 mph, it will, by law (of nature) get better mileage than at 60 mph. You can't fight that Sv factor.

If you optimize the system to produce the most power per unit fuel at 55, and then change the gearing to go 60 at the same engine speed and throttle setting (make the top gear ~10% higher), the maximimum fuel mileage will go with it--the max mileage will be slightly lower, but the max mileage will be at the higher speed. One point I am trying to make is that an unenacted regulation is forcing automakers to build cars to get their best mileage at speeds at which people do not drive.

Your equation calculates the power required. It doesn't take into account whence the power comes. If it is at the expense of running the engine at a less efficient setting, you can actually burn more fuel and take more time to go somewhere because the engine requires more fuel per power produced. If the engine produces 20% more hp per pound of fuel at 10% higher speed, and if the power required to go 10% faster is less than 20% more, the system is more efficient at the faster speed. So you can optimize the system for maximum mileage to any speed within reason.

What if you had (as some European cars do) a constantly variable transmission? At what throttle setting and speed do you run the engine, regardless of the speed of the vehicle? Easy. When accelerating, the one where the most torque is produced per unit fuel. When cruising, where the most power is produced per unit fuel. Luckily, these are usually nearly the same number.
 
2008-06-05 06:44:42 PM  
2002 Nissan Maxima SE. I drive extra careful to preserve mileage, I get about 20.4 Being heavy pawed, I only lose one mpg. Worth it when you have 255hp to play with
 
2008-06-05 06:46:31 PM  
Surpheon: Road load power is approximately:

Pr = (CR * Mv * g + 1/2 rhoa * Cd * Av * Sv^2) * Sv

CR = coefficient of rolling resistance
Mv = mass of vehicle
g = gravity
rho a = density of air
Cd = drag coefficient
Av = frontal area of vehicle
Sv = vehicle speed

Distributing the Sv means there's an Sv^3 term there (for wind resistance & drag). I thought for sure it'd only be Sv^2. I'm only aware of one other thing in nature that has 3rd order terms and that was something from electromagnetism (some effects were inverse distance ^3). So color me surprised. Are you sure there's not a mistake here?
 
2008-06-05 06:56:37 PM  
Stoffel:
Distributing the Sv means there's an Sv^3 term there (for wind resistance & drag). I thought for sure it'd only be Sv^2. I'm only aware of one other thing in nature that has 3rd order terms and that was something from electromagnetism (some effects were inverse distance ^3). So color me surprised. Are you sure there's not a mistake here?


Straight from the textbook although I've never done the derivation of this one (I believe it has some empirical components).

The third power term makes sense. The pressure resistance increases with the square and the mass flow increases linearly. When you reduce flow through a fan or pump (feeding a turbulent flow system) you see power vary with the cube of flow. Pressure is varying with the square and the mass flow that the pressure is acting upon is varying linearly.
 
2008-06-05 07:11:04 PM  
So that's what the OverDrive button on my Camry is! I should remember that next time I go on the highway.
 
2008-06-05 07:17:12 PM  
My 2003 Bimmer (530i) get's a smooth 30MPG on the highway with the air on if I just drive'er easy and keep it around 60-65. And it's paid for. Granted I could best that by 6MPG if I traded in for a Yaris...but, nah.
 
2008-06-05 07:54:56 PM  
Tourney3p0: voidrunner:

Because you talk like you are a 19 year old punk, who, and you kept comming up with more reasons why you were right, but didn't state until it came convienent for your argument. and this car i have yet to see a pic of, or at least the engine, and tranny

I'm noticing you and impaler's grammar keeps getting worse and worse the more flustered you get. Why does it matter what the facts are? My statement was that slowing down doesn't always net better gas mileage. This is a fact. The details behind it are irrelevant.

Why do you want to see my engine and transmission? It's nothing special. The engine is a 350 bored and stroked to 383 with a SuperRam intake. The transmission is a TH400 changed from a 3 speed to a 6 speed. It looks pretty much stock. There's nothing special or awesome about any of it.


So it's a TH400 with a gear vendors overdrive, running tuned port injection from accel. Sounds like a pretty mild street build, geared for high-speed cruising or even (GASP!) MPG. You coulda just said all that earlier, at least three of us would have understood and gotten on with our lives.

Sheesh!
 
2008-06-05 08:02:41 PM  
TRIAC Electric Car. Range: 60-100 Miles. Cost: 2 cents per mile gas2.org
 
2008-06-05 08:15:59 PM  
Four Horsemen of the Domestic Dispute:

Tell hubby the A/C runs off the electric motor (it does).
IF you are travelling over 40 miles per hour the gas engine is running anyway, thus charging the hybrid battery. The only time the A/C really robs the batteries is under 40. At the end of the day you're still ahead on MPG. And, if you are happy and in good shape he is more likely to get the 'giggity'.

/52mpg with mine.
//I can't wait till the Gen3 comes out....


I'll let him know on that, thank you!! He thinks he's a know-it-all on EVERYTHING!!!
Gen3? Schweeeeeeet!...
 
2008-06-05 08:21:56 PM  
gotrootdude: TRIAC Electric Car. Range: 60-100 Miles. Cost: 2 cents per mile

BWAHAHAHAHAHAAAA!!!XD!!

That looks like that 2-door Speck from that old McDonald's Commercial!

/Do Want Though...
 
2008-06-05 09:39:46 PM  
Fuel economy myths debunked: Even if you keep your windows up, your AC off, lose 50 pounds -- you're going to get the same crappy mileage
==============

Less weight is better mileage. And asshole could tell you that.

/Mythbusters proved windows down is more effective under 55mph, windows up is more effective over 55mph
//Of course, that's in comparison to the AC.
 
2008-06-05 10:16:09 PM  
Great Janitor: Nothing mentioned was really news to me. I do wish I had that episode of Mythbusters on my computer (the tailgate issue one) so I could burn it to 50 DVDs and put them under the wiperblade of every truck I see in the parkinglot with their tailgates down (exception for those who's tailgates are down because they are hauling stuff), and for those with that netted tailgate.

Back when I had a car, the tailgate was pretty much the first thing that broke. I mean, you're pretty much constantly dropping heavy stuff on it while loading, it's not really surprising that it stops latching after a while and has to be removed or left down (or fixed, but the 750$ was probably two or three times the resale of the vehicle at that point). I don't see my problem being unique, really, I'm betting a lot of what you're seeing is the equivalent of the obligatory dinged door on a 70s beetle rather than doucebaggery. Unless you park in front of a frat or something.
 
2008-06-05 11:41:19 PM  
tricycleracer: MetaRinka: Motorcycles really are the gas sipping way for personel transportation.

No one can disagree with this.

The problem is that personal safety is still worth more than fuel efficiency to most people.

An interesting psychological study would be to determine at what gas price people begin to discount safety.


About when it was $3.50/gal here in Southern California. Anybody else shed the cage recently and at what price?
 
2008-06-06 01:19:52 AM  
The idling thing is not true for my car. I have a '77 caprice with a 4 barrel carb. Shutting my car off will not save me gas. Starting my 350 V8 will dump a fair amount of fuel into the carburetor, lowering fuel economy.
 
2008-06-06 02:01:35 AM  
iammess: I have a '77 caprice with a 4 barrel carb. Shutting my car off will not save me gas.

Shutting it off forever will.

How do you tolerate such an inefficient, lumbering POS?
 
2008-06-06 03:56:05 PM  
Good gravy...

A topic just BEGGING for Mythbusters pictures, and the only one I saw was of Adam and Jamie, with no Kari pics at all.

You guys are slipping...
 
2008-06-06 07:25:08 PM  
Yankees Team Gynecologist: iammess: I have a '77 caprice with a 4 barrel carb. Shutting my car off will not save me gas.

Shutting it off forever will.

How do you tolerate such an inefficient, lumbering POS?


hey, don' be hatin' on his box:
www.rides-mag.com

/dirty, dirty hotlinker
 
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