Hypermiling: A new hobby for gas savers & environmentali

Our "pub" where you can post about things completely Off Topic or about non-silent PC issues.

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AZBrandon
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Post by AZBrandon » Thu Feb 14, 2008 8:34 am

A 1000-watt peak rated stereo won't typically draw more than 300-400 watts continuous. Now on a cheap economy car with an 80 amp alternator, a 400 watt continuous load is over 30 amps, with the potential for those spikes up to nearly 80 amps when it hits notes at maximum power. That's how stereos kill batteries and alternators. If you get a bigger alternator however, like how trucks use 150-300 amp alternators, the problem goes away.

Anyway, 400 watts is about 0.5 horsepower. You really can't even measure the difference. Compare that to air conditioning that uses 5 to 10 horsepower worth of power on a 40-50% duty cycle in most cases. A/C will easily increase fuel consumption by 0.3 gallons per hour. At highway speed, it's not much of a big deal, but if you're mainly doing stop and go, that 0.3gph really adds up.
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Post by jimbo7707 » Thu Feb 14, 2008 5:21 pm

:D :D :D :D :D

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:D :D :D :D :D

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Post by Brian » Fri Feb 15, 2008 2:29 pm

When I'm commuting on my bicycle, I'll often pull up next to a Prius at a red light. I would love to pretend to roll down the window on my bicycle, then call out to him "Your vehicle is destroying the environment!" Mostly because it would be funny.

That has yet to happen, as I have literally never seen a Prius being driven with the windows down.

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Post by klankymen » Fri Feb 15, 2008 11:10 pm

Yeah, with the amount of smug that hybrids emit, it's best to keep your windows down.
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Post by NeilBlanchard » Thu Apr 17, 2008 7:58 am

Hello,

An update of my Scion xA's gas mileage: this government web page says that the "new" combined mileage is 30mpg. My overall average for the three years that I've owned it is 37mpg+. (The other two drivers that have shared their mileage average 35mpg.)

The most recent tank full, I got 42.33mpg -- which is the best I have ever gotten! I have inflated my tires to 38psi, I drive <60mph, I coast in neutral as often as possible trying to anticipate stops, I draft on the highway when possible, I don't use the defrost setting as this always turns on the A/C, and when I'm in stop and go traffic, I am accelerate very slowly and I try to time the gap to the vehicle ahead of me so I don't have to use the brakes.
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Post by aristide1 » Sun Apr 27, 2008 8:50 am

Problem solved:

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Post by aristide1 » Sun Apr 27, 2008 8:59 am

Seriously though, I used to do 600+ miles on a weekend through the Catskills. I swear on this round trip I would coast over 70 miles. Coming down the mountain just west of New Platz was a 7+ mile coast by itself. Of course I used a lot of gas getting up the mountain, made worse because I couldn't go fast enough to stay in high gear, but still, most coasts were over a mile. One was 3 miles at about 80mph, I like that one. Occasionally I could build enough speed to overcome the next smaller uphill through my coasting speed alone.

My EPA highway mileage for my car is 29, and I average 32, also mostly highway, but Mobil One has something to do with that as well, worth 1mpg all by itself.

In the summer I use the AC only on downhills and as a form of braking, often downshifting with the AC on to cool the car off quickly. The wear and tear on the trans fluid is another issue.

Neil's high pressure tires are going to wear out quicker if they are overinflated, potentially canceling out any real financial savings.

OT - Years ago I read an article about running shoes. Their cost of ownership was over 30 cents a mile, which at the time was higher than the ownership of my car. It was ridiculous.
Last edited by aristide1 on Sun Apr 27, 2008 12:02 pm, edited 1 time in total.
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Post by santacruzbob » Sun Apr 27, 2008 11:26 am

nutball wrote:Another tip which wasn't immediately obvious to me was to keep the car in gear (high gear) when decelerating and braking until you almost stall. I had naively presumed that coasting in neutral would use less petrol, but it seems that that's wrong. In neutral the engine management system needs to use fuel to keep the engine going -- if you coast in gear the momentum of the car keeps things turning. This can save a fair bit of fuel in stop-go situations like urban driving.
If I understand this right, it'd be creating a lean condition which is about the worst thing you can do to an engine.. I suppose if the spark plugs didn't fire it could work, but I've never heard of such a setup

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Post by aristide1 » Sun Apr 27, 2008 12:02 pm

I doubt the auto computer would allow any ultra lean condition to exist as I believe it makes for very high emissions.

So for gas usage at idle vs. decelerating, what perecentage of your driving happens under those conditions?
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Post by AZBrandon » Sun Apr 27, 2008 1:16 pm

santacruzbob wrote:If I understand this right, it'd be creating a lean condition which is about the worst thing you can do to an engine.. I suppose if the spark plugs didn't fire it could work, but I've never heard of such a setup
It's not lean because there's zero fuel. A lean mixture would be one where you're injecting fuel, just not enough to keep the cylinder temperatures down and assure even combustion. When coasting in-gear, there's zero fuel. Engines will kick the fuel injectors back on at various engine speeds though depending on programming and conditions. Here's a page from my 97 Civic's manual showing the various RPM that it will re-activate the fuel injectors.

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Post by aristide1 » Sun Apr 27, 2008 3:47 pm

If down shifting gets your engine to redline you're overdoing it just a tad.
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Scion xA RS 2.0

Post by NeilBlanchard » Sun Apr 27, 2008 6:57 pm

Hello,

I got 43.54mpg on the most recent tank. Compare this with the "new" EPA combined of 30mpg, and 34mpg highway...

Keep on coasting in neutral -- the idle on my car is ~600RPM, and that's a lot better than keeping it in gear; because I coast a lot further!
Last edited by NeilBlanchard on Wed May 14, 2008 7:14 pm, edited 1 time in total.
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Post by aristide1 » Sun Apr 27, 2008 7:45 pm

In the days of the Chevy Vega, with no power steering or power brakes, it was very conceivable to turn the engine off during a long coast, and later restart the car just by putting back in gear (stick shift).

NYC taxi drivers typically go to neutral at red lights, though I don't know if this saves gas, simply reduces transmission heat and fluid breakdown, or both.
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Post by AZBrandon » Sun Apr 27, 2008 8:58 pm

aristide1 wrote:If down shifting gets your engine to redline you're overdoing it just a tad.
No no, that's the other fuel cut. Basically if you lift off the gas pedal all the way, it cuts the fuel injectors as long as the engine is over 1000rpm or so. So if you're turning 1700rpm in 5th gear and lift off the gas because the light up ahead just turned yellow, it cuts fuel entirely. As was mentioned above, you do coast further in neutral, so it's basically just a distance judgement. If the light turns yellow/red when you're fairly close to it, you can coast in-gear and make it. If you're a bit further away, then you can put it in neutral and get the extra coasting distance to reach the light.
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Post by Blacktree » Sun Apr 27, 2008 9:06 pm

All these MPG figures are nice and everything, but how many gallons of fuel do you use in a week? My car's fuel efficiency isn't anything to brag about. But I still only use about 3-4 gallons of fuel per week. My daily commute is only 7 miles total.

I guess you could call that "hypomiling". :P

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Post by wim » Sun Apr 27, 2008 9:32 pm

nutball wrote:Another tip which wasn't immediately obvious to me was to keep the car in gear (high gear) when decelerating and braking until you almost stall. I had naively presumed that coasting in neutral would use less petrol, but it seems that that's wrong. In neutral the engine management system needs to use fuel to keep the engine going -- if you coast in gear the momentum of the car keeps things turning. This can save a fair bit of fuel in stop-go situations like urban driving.
interesting. i have used neutral for long downhills too and i wasn't aware of this, but it makes sense..

AZBrandon
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Post by AZBrandon » Mon Apr 28, 2008 8:36 am

Blacktree wrote:All these MPG figures are nice and everything, but how many gallons of fuel do you use in a week? My car's fuel efficiency isn't anything to brag about. But I still only use about 3-4 gallons of fuel per week. My daily commute is only 7 miles total.

I guess you could call that "hypomiling". :P
I totally agree with you on that one. I track everything in Excel, so I have my numbers handy for the years 1997-99 and 2005 forward. My gallons used is:

1997: 524
1998: 479
1999: 385
2005: 385 (again, coincidentally)
2006: 286
2007: 237
2008: 63 (so far)

That is all with the same exact car, by the way. I do fly every so often, although the way oil prices and thus airline ticket prices are going, flying may be an extremely rare thing for me now, like perhaps only once a year. Since fuel is money and I'm not made of money, the incentive to save gas is largely an economic one. I did also just get married last November, so my family usage is up, but per capita it's still pretty similar since my wife and I carpool whenever possible and do our best for trip reduction.

I agree though, looking at gallons used rather than just miles per gallon is the most important thing. That tends to be self-correcting as the price of fuel increases since the more expensive fuel is, the less that people will want to use fuel, so it doesn't take the lion's share of their budget.
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Post by sthayashi » Tue May 13, 2008 4:08 pm

Interesting thread here.

One thing I've discovered is driving a little more slowly can have much larger impact on your mileage. On the highways, 60 MPH is more fuel efficient than 70 or 80 MPH.

Locale and commute appear to dictate my mileage, FWIW. Pittsburgh is not friendly to these tricks when you're in town. Lots of stop signs and stop lights at the bottoms of hills, and too many places where it's a single lane and the person in front of you is attempting to turn left.

Something I've found myself doing with modest success is using the cruise control in areas where you may not consider using CC. It does a better job of maintaining constant speed better than I am, which is important when going up a series of hills. If you're in a flatter area, coasting is better and easier.
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Post by mr. poopyhead » Tue May 13, 2008 8:37 pm

i've always tried to be a fuel efficient driver... looking ahead, timing intersections to avoid braking, etc.. but i've never really calculated my fuel consumption until tonight...

this is a fun little webpage: http://www.oee.nrcan.gc.ca/transportati ... -input.cfm
Fuel Cost
$64.56

Distance travelled
752 km
467.29 miles

Fuel Amount
48.5 litres
12.81 US gallons
10.67 Imperial gallons

Cost of Fuel
$1.33 per litre
$5.04 per US gallon
$6.05 per Imperial gallon

Fuel Economy
6.45 litres per 100 km
36.47 miles per US gallon
43.8 miles per Imperial gallon


Mileage Costs
8.5851 ¢ents per km
13.82 ¢ents per mile
i dunno... 6.45/100km (sorry i refuse to use imperial units, :P) doesn't seem that great. i think i remember getting close to 900km on a tank last year, but i'm doing a lot more city driving lately. what else could i be doing? i always try to drive at the highest gear and lowest RPM. i dunno the physics behind it, but intuitively, it seems like the way to go since wind resistance increases exponentially with speed (not sure if its the square or cube...) but at the same time, i'm not sure if the lowest RPMs are the most efficient for the engine...

i'm driving a '92 TDI jetta. i guess it's a little rusty and stuff so maybe it won't ever be as efficient as a new car. or maybe my shifting technique sucks...

i'm still looking for a restaurant that will gimme free used oil to throw into this thing...

there also some useful stuff here:
http://en.wikipedia.org/wiki/Fuel_econo ... _behaviors
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Post by sea2stars » Wed May 14, 2008 5:16 pm

I was curious how much this would really alter my MPG and decided to follow some of the hypermiling advice over the course of my last fill up. I drive a 2005 Scion tc with an EPA MPG rating of 22/30. I drive a combo of highway and local roads and managed to get close to 33MPG. Hah. I think the drive up to Boston this weekend helped. I was the only person doing the speed limit and I was passed by every vehicle on the road; big rigs included. All I could do was laugh and thank them all for the free gas. If all of these people can afford to kill their gas mileage, then they have no reason to complain about high gas prices.

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Post by jaganath » Thu May 15, 2008 1:59 am

wind resistance increases exponentially with speed (not sure if its the square or cube...) but at the same time, i'm not sure if the lowest RPMs are the most efficient for the engine...
IIRC drag rises with the square of the speed, but (engine) power required rises with the cube of the speed. this is why, for example, the Bugatti Veyron only uses 80bhp at 100mph but needs 1000bhp to reach 250mph.

bottom line, a constant 55mph is the most efficient speed for most cars. for every 10mph you go above that fuel consumption increases dramatically.

re: keeping RPMs low, seems like the right strategy:
http://www.fueleconomy.gov/feg/driveHabits.shtml
When you use overdrive gearing, your car's engine speed goes down. This saves gas and reduces engine wear.
gasoline engines are actually least efficient at low revs because of pumping losses, but diesel engines, which do not have a throttle, are probably equally efficient across the whole rev range.
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Post by klankymen » Thu May 15, 2008 5:53 am

jaganath wrote:bottom line, a constant 55mph is the most efficient speed for most cars. for every 10mph you go above that fuel consumption increases dramatically.
I don't know about dramatically.... driving at 60 kmh gets me about 5l fuel consumption, going up to 100 puts me at 7.5l, and even up at 140kmh I'm only using about 10l. Once you go over 140 (87mph), is where the dramatic rise starts... at 180kmh I'm up at like 20l.

Far more damaging to my low usage is having to brake. If your crusing down the street at a nice 100, and then some slowpoke ahead of you is going 70, and then when he turns off you accelerate up to 100 again, you're using like 20l/ckm for the acceleration... also traffic lights and the like, or short periods of speed limits. If I could just drive 80kmh all the way, with no braking, I would get 5-6l probably, but with all that I'm more like 7-8l (half again more)
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Post by AZBrandon » Thu May 15, 2008 7:46 am

jaganath wrote:gasoline engines are actually least efficient at low revs because of pumping losses, but diesel engines, which do not have a throttle, are probably equally efficient across the whole rev range.
You used the wrong word there. You said revs when you meant absolute manifold pressure. Gasoline engines are most efficient the lower the engine revs are because the lower the revs, the higher the manifold pressure at any given power level. This is why the Corvette uses an extremely tall 6th gear, so it only has to run about 1300rpm at 65mph. The Corvette has over 400hp and wide, high rolling resistance tires but can do 30mpg on the highway because of that super-tall final gear letting it run very low engine revs.

Older diesel engines have no throttlebody, thus they do not pull any vacuum, and lack that type of pumping loss. What the modern age has brought us however is diesel engines with throttlebodies, so they can pull vacuum and pass emissions along with gasoline cars implementing atkinson cycle so they can run higher manifold pressure at any given power level. We're seeing the real world performance capabilities of gasoline and diesel engines approaching each other in terms of BSFC.
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Post by jaganath » Fri May 16, 2008 1:56 am

We're seeing the real world performance capabilities of gasoline and diesel engines approaching each other in terms of BSFC.
I don't know about that. atkinson cycle engines are still pretty rare in mass-produced cars and the thermal efficiency advantage of diesels has always been better than gas. of course HCCI is an attempt to make gas engines more "diesel-like", so I suppose in that way the line is being blurred between diesel and gas.
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Post by Cistron » Fri May 16, 2008 2:19 am

Hmm, let's see. A somewhat acceptable european diesel car runs at 5litres per 100km, that's roughly 56 miles per gallon. An efficient car 3 litre car, such as the Audi A2, will do 94 miles per gallon. That's of course with moderate driving around 2000rpm.

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Post by NeilBlanchard » Mon May 26, 2008 5:58 pm

Hello,

I heard about a really useful website (on the Popular Mechanics web site), for hypermilers:

http://ecomodder.com/

They have a very active and helpful forum.
Sincerely, Neil
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Post by AZBrandon » Mon May 26, 2008 8:25 pm

Cistron wrote:Hmm, let's see. A somewhat acceptable european diesel car runs at 5litres per 100km, that's roughly 56 miles per gallon. An efficient car 3 litre car, such as the Audi A2, will do 94 miles per gallon. That's of course with moderate driving around 2000rpm.
Well, remember that there's a lot of US readers on this forum, and our gallons are a lot smaller than your gallons. :)
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Post by NeilBlanchard » Tue May 27, 2008 3:35 am

Hello,

Yes:

1 UK gallon = 1.20095 US gallons

Or the inverse:

1 US gallon = 0.8326738 UK gallons

So, 5 liters / 100km = 1.32086 US gallons / 62.13712 = ~47mpg

[Corrected -- I did get the last part right... :oops: ]
Last edited by NeilBlanchard on Tue May 27, 2008 4:29 pm, edited 2 times in total.
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Post by nutball » Tue May 27, 2008 3:58 am

...never mind

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Post by Cistron » Tue May 27, 2008 4:36 am

Oh sorry, I just typed in gallon on google. I'm not used to any non-metric units at all.

I think Neil has mixed it up as well ;)

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