Talk:Fuel efficiency

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I think that details of fuel efficiency ( = energy-efficiency --well, almost) should be covered in articles about say automobiles, the steel industry, railroads, etc. Then under each of the headings of transportation, industry, commercial, and residential, there should be a subsection on energy efficiency (includes fuel efficiency). For transportation, this would compare the energy efficiency of various modes of transportation and briefly explain why some modes are sometimes more efficient than others. Then "fuel efficiency", "fuel economy", "energy efficiency", "energy efficiency", etc. would all link to a common article which would define the terms, etc. (something like what I've done under "Energy efficiency terminology"). It would have a lot of links to articles about energy efficiency for a specific activity such as transportation, railroads, industry, aluminum production, etc. DavidLawyer 22:23, 14 June 2006 (UTC)

I don't see why this article should be exclusively about fuel efficiency of vehicles. The concept of fuel efficiency applies to any machine which does work. A section on power stations would also be useful. I added the trivia on the space shuttle and humans because it's interesting. Yes, food energy is not interchangeable with gasoline. But equally gasoline is not interchangeable with diesel or hydrogen. Seabhcán 15:20, 23 February 2006 (UTC)

As it is, the article talks mainly about the fuel efficiency of cars. Maybe most of that discussion should be split to a different article: Fuel efficiency of vehicles perhaps ? StefanoC 15:34, 23 February 2006 (UTC)
Yes, That sounds like a good solution. How about Fuel economy in automobiles?, to distinguish it from the slightly different concept of fuel efficiency. Seabhcán 15:41, 23 February 2006 (UTC)
Split request posted into the article. Are there deadlines for the discussion ? StefanoC 08:12, 24 February 2006 (UTC)
The current article focuses almost entirely on gasoline-powered cars, although the nr. one reason for buying diesel-powered cars is fuel economy. I suggest naming the new article Fuel economy of gasoline vehicles. This allows new types of fuel to be inserted, i.e. electrical, vegetable oil, hybrid, diesel. These fuels may have characteristics which are not shared with other types of fuel, regarding economy.

This page is about Fuel Economy instead of Fuel Efficiency. Although the author does explain the difference between the two in the first paragraph, the rest of the article is about Fuel Economy. The problem for me is that readers get confused because the first paragraph is in contradiction with the rest of the page.

In my opinion the whole article apart from the first paragraph should be renamed to Fuel Economy and this page should explain more about causes and effects of Fuel Efficiency.

I've just edited the article to reduce this problem. It's really about fuel efficiency and fuel economy, which is why the latter is a redirect here. --SFoskett 13:24, Apr 27, 2005 (UTC)

But fuel efficiency is not related to engine displacement. In my opinion it tells you how much energy can be extracted from a certain amount of fuel. When the power output of 180 hp is really applied it will use a lot more fuel then the 120 hp did at maximum power so you would have to calculate the amount of fuel the 180 hp engine would use at a 120 hp output to be able to say anything about fuel efficiency.

Hope this makes any sense.

In addendum to the most recent comment. Usually a higher-output engine uses more fuel, as was just said. The reason is that the higher-outputting engine often has higher volumetric efficiency, or ability to fill the engine with air. Part of the increase in power you mention is due to the revised intake system, which gets more air into the engine per revolution. Since you need air to burn a given amount of fuel (14.7 parts air : 1 part fuel), the engine with higher volumetric efficiency can burn more fuel per revolution and thus create more power, even if the "fuel efficiency" is the same. I think what you mean by fuel efficiency is more properly referred to as thermal efficiency, or the proportion of the energy released in the combustion process that is converted to mechanical energy to drive the car rather than lost as heat. For example, the Toyota Prius uses an Atkinson cycle engine that stresses thermal efficiency (extracting all the work from the energy produced by the burning of fuel) at the expense of volumetric efficiency (fully filling the cylinders with air). Thus the Prius is quite fuel-efficient even though the specific output is less than spectacular (something like 75 hp from 1.5 liters).

Also, a big factor in specific output is the RPM at which the engine operates. Roughly stated, an engine that revs twice as high will make twice as much power, all other things being equal. Thus the high-revving engine will have twice as high a specific output, but will burn at least twice as much fuel in the process. That's why an F1 car getting 700+ hp out of a 3L motor isn't an econocar compared to an average sedan motor which gets 200 from the same displacement. -jspater

Fabled 150 mpg technologies[edit]

I think everyone here has probably heard the apocryphal story about a guy who found a way to make a Camaro get 150 mpg with some secret technology but the big oil companies "silenced" him. Well I have no idea how much truth there is to this, but Wikipedia would be a great place for anyone who has a clue as to the truth of this to spread the word. If there is indeed a technology like this that would truly piss off the oil companies, let's post it up here and there will be nothing they can do about it.

There is no truth to these stories, of course. There's only so much energy in a gallon of gas, and since the fuel economy of a car is dominated by factors OTHER than the engine (namely the weight, transmission and body shaping), nothing you can do to the engine is going to quadruple your gas milage. These stories are urban rumors that gain currency with the current "sticker shock" price of gas; they were huge in the 1970s for instance. Maury 22:51, 7 March 2006 (UTC)
Getting 150 mpg isn't so difficult. Highly experimental vehicles have been able to get fuel efficiencies in excess of 1000 mpg for a few years now. I think the scepticism comes from a misunderstanding. You're not going to get a heavily laden SUV driving at 90mph to be very fuel efficient. But if you get a small to medium sized car there are things you can do.

Weight Minimise all the weight inside the vehicle, that means stripping out the seats, no luggage, go naked, lose weight, remove all the internal trim from the vehicle Engine Get it cleaned and tuned up, use the most appropriate engine oil, etc. I'm not an expert in car maintenance, but there are small things you can do. Driving Drive at around 55mph in the highest gear. Use the clutch when going downhill, and re-engage when you're near the bottom of the hill--Manc ill kid 12:09, 8 June 2006 (UTC)

As an aside to this debate, I find it interesting that the article states that a 'suitably modern supermini' may achieve something like 57mpg (UK) at 56mph... when my last car was a 1991 model that achieved close to 60mpg at that speed (when I could bring myself to drive that slow - normally mid 30s to low 40s - still, nearly as good as a Prius in the raw), was shaped like a box, and had a pig-simple engine (save for the single point fuel injection, more or less an electronically controlled carburettor) and a 4-speed gearbox... it wasn't fast, but it was quick enough to keep up with and regularly overtake motorway traffic. Does 'suitably modern' mean from 1980 onwards (approximately when the model line was birthed)? My current 1998 car with half the mileage, I haven't had opportunity to properly test, but I know I get notably worse economy in similar conditions (low to high 30s... fair play, it is a larger engine and slightly heavier, but it's got more sophisticated management, smoother shape, more and taller gears, etc)... are we slowly drifting backwards on this point? I'm reminded by the story of someone who had a Peugeot 205 diesel in the mid 80s that would regularly do more than 70mpg whilst still having (borderline :) acceptable performance... and this wasn't modified or anything out of the ordinary, but in fact fairly close to (and worse than) the manufacturers claims. Nowadays we need something with 3 fewer seats, minimal luggage capacity, dodgy handling and probably minimal extra performance to achieve the same thing? (Smart CDi)... or 1 less seat, similar get-up-and-go, and a suite of trick electronics and transmission? (The sadly discontinued Lupo 3L - it would, at least, have been more efficient around town - itself derived from an early 80s far-less-tricked-out design that pushed close to 80mpg in realworld testing). Gaaaah. People may speak of a conspiracy... I'd be inclined to agree with them. The technology advances we've had in 25 years SHOULD have given us the 150mpg, or at least the 100, by now... - Tahrey, 13/1/07 —The preceding unsigned comment was added by 82.46.180.56 (talk) 22:13, 13 January 2007 (UTC).
I also find the comment about achieving near 60MPG in a modern minibox. My 99 Corvette gets above 40MPG at 55-57mpg,a car I might add that is not designed for great fuel economy. If a modern econobox can't achieve better than 60MPG at those speeds, something is wrong IMO.

Ucntcme 03:16, 5 November 2007 (UTC)

Ambiguous gallons in 'mpg'.[edit]

I have just asked a question about the format of fuel efficiency units at: Talk:Gallon. Bobblewik  (talk) 13:00, 20 Jun 2005 (UTC)

Not 150 but I have been involved withn a team some time back that did achieve 108 mpg.

"accelerate as gradually as possible"[edit]

I think this is incorrect. The best fuel economy is if you accelerate to the most fuel-efficient speed (45-60mph) smoothly but quickly, shifting gears to keep the engine RPMs up near the maximum of the torque curve until you get to speed. Google on "ecodriving". I'm not clear enough on my engine physics to be 100% sure on this.

More on "accelerate as gradually as possible"[edit]

Years ago, Car and Driver Magazine reported on some tests by BMW that measured the net amount of gas required to get from A to B, instead of the momentary use-fluctuations at different rates of acceleration. C&D reported this: For distances of a mile or more, accelerating at about 2/3 acceleration and holding steady at the desired speed yielded better gas mileage than slow acceleration to the desired speed. Volumetric efficiency was cited in explanation.
--- In the city, brisk acceleration has a collective benefit. Even when the distance to the next light is short, moving smartly through an intersection allows more cars to get through, eliminating one or two go-stop-idle cycles for them. Obviously, there's a trade off here, but those who prefer gradual starts ought to be informed of the costs of their preference to others.
--- Since heavier vehicles with larger cross-sections are more efficient at lower speeds than lighter vehicles with smaller cross-sections, it might make sense for SUVs, minivans, larger pickups, and crossovers to be included in the highway left-lane ban for trucks, using a height criterion.
(apologies--this may show up twice--new user) Bo8ob (talk) 20:45, 15 June 2008 (UTC)

records[edit]

how about some info on those world records for fuel efficiency? the experimental cars that get 10,000 miles to the gallon and so on. - Omegatron 14:30, July 17, 2005 (UTC)

Difficult do do in a meaningful fashion though... what's a solar car get? Maury 22:51, 7 March 2006 (UTC)
Solar cars use about 40 kWh to travel 3000 km at an average speed of 90 kph or so. You can debate how to turn that into mpg. I think the 10000 figure is about right for mileage marathon cars, also bear in mind they are travelling quite slowly.Greg Locock (talk) 03:42, 25 August 2008 (UTC)


Better Fuel Economy Tips[edit]

It might be best to set aside a whole new topic just for tips about getting better fuel economy out of vehicles.

Another section might be dedicated to fuel economy 'mods' that (at least in theory) definitely work, versus the pure quackery that gets really popular when fuel prices spike a bit.

First off, "gradual" acceleration is just wrong, if "gradually" accelerating means you're staying in first, second and third gear longer, you may as well be pouring gas onto the street. You can prove this to yourself with your car's built-in real-time mileage doohicky, or with a 'scanguage' gadget plugged into your OBD port and monitoring fuel consumption and real-time mileage. The longer you spend in lower gears, the worse the mileage you'll get. Shift toward the highest practical gears as quickly as practical, and then 'gradual' acceleration will win... once you're in 4th or 5th gear.

Also, it should be pointed out that though fuel economy is a fine goal, that we're still not in bad enough shape that you NEED to dump a perfectly good vehicle to save 10MPG with a new car. To save even 10MPG, it could take a decade, even longer to pay off the difference in a new car and a car you already owned, even at $3 or more per gallon. Of course, if you're talking trading a truck/SUV for a little car and a 30+MPG difference, then it could take less time than paying for the car to make up the difference with only a modest increase in fuel prices, especially if you have little or no 'equity' in a truck/hybrid you're making payments on. The more you drive, the quicker any savings add up.


Potentially Expensive Fuel Savings:

1. Get a car that is fuel efficient to begin with.

2. When you get your efficient car, get a manual transmission. However smart an automatic transmission's 'brain' is, it can't see the road ahead like you can, and it can't predict what gear to be in as intelligently, as a result.

3. Get a car with real-time fuel consumption monitoring, or buy an add-on like a '[Scangauge]' to use until you've established the optimal driving patterns for your vehicle.

4. Don't get a car that keeps the A/C on all the time to keep the windows 'clear', or with 'climate control' that maintains a preset temperature without giving you explicit control to turn the A/C absolutely off, even with the vent fan ON.

"Free" Fuel Savings:

1. Keep track of your fuel consumption. A notepad and a pencil will do. A simple log of odometer+how much gas you put in, with whatever accuracy the odometer and pump gave you. You can't tell if you're saving gas if you don't keep track.

2. Check your tire pressure often, keep tires inflated properly & balanced/aligned. For safety AND economy. "Once a month" is recommended for checking pressure, but you should make sure the tires are equally and properly inflated more often than that.

3. You don't need to "pull G's" when the light turns green, and you don't need to go the speed limit (or higher) right up to a red light.

4. Time your arrival at lights so they will be green and traffic will be moving more often than not. If they aren't going to be green when you get to them, don't be in any hurry to reach them, and you won't feel so bad.

5. Manual: Coast out of gear everywhere you can safely (and legally) do so. It adds up quickly. Most states make it an infraction to drive 'down-hill' in neutral, but it's usually your most economical gear for every other situation. During extended downgrades at highway speeds, many modern engines will shut off fuel supply completely.

6. Keep an adequate enough following distance that you can pace the car(s) ahead and virtually never brake or accelerate. (The dimwit who tailgates you now would tailgate even if you were tailgating the car ahead, and driving 100MPH.)

7. Get into the highest gear you can, as quickly as you can when accelerating.

8. Take a hill in the highest gear you can, even if it means going a little faster up-hill.

9. Off the highway, open the windows. On the highway, at higher speeds, shut them, the aerodynamic drag is worse, possibly worse than running A/C.

10. A/C is "free" when rolling down-hill, in gear. You really can live without A/C, with the vent fan on, even in 100+F temperatures. Bring some water with you.

11. Don't go excessive speeds on the highway. Don't go excessively slow, either.

12. Use the cruise control on flat, open highway. Set a sane speed, and let the computer stick to it.

13. Don't treat your car as a mobile storage shed/dumpster. Shovel the garbage and useless junk out of it once in a while. It may even stink less.

14. Keep the windows absolutely sparkling clean and residue free, and you won't need to operate the A/C as much in damp weather to keep them clear. You'll also be able to see better at night.

15. Don't drive around in parking lots looking for a spot. Half the lot is almost always empty, so look in the empty half for your spot.


Regarding #5: No, this is not a good idea in modern engines. Most will all but shut off fuel supply if the manual transmission is in gear and the clutch in engaged, but will have to add fuel to maintain idle speed if the engine is not being pushed along by the motion of the drivetrain from the ground up. In particular GM LS* engines are this way. If you do have a manual, you can often save fuel by "winding it up" in a lower gear and jumping to a higher gear, skipping in between. By using fewer shifts you keep the motor running a constant rate of increase rather than ups and downs. this is, however, dependent on the power output of the car compared to it's weight and gearing. As the saying goes "Your mileage may vary".
Regarding 12,this is also not true. Learning to manage you fuel speed by foot pressure is more effective. Cruise control systems today are designed to maintain a given speed, not maximize fuel economy. If you pay attention you will find they hunt and flux, trying to adapt to the slight changes in road surface. A constant use of fuel will lead to better economy even though your speed may vary within several units of measurement.
Regarding 14, this is also not true.
Air conditioning is not needed to keep windows from fogging over air flow works fine, and a clean window will fog over as much as a dirty one. Oh and on anything with a V-8 A/C is essentially free. All accessories combined (which means power steering and power brakes, alternator, etc.) account for less than 2.2% of the energy draw from the engine.
  1. 8 is also questionable as bogging an engine will allow to to do it, but dump fuel and increase emissions to do it. It can also cause excessive engine wear and tear as well as cause issues on the driveline.
Regarding tire pressure ,even pressre is not a given. Depending on alignment, road crowning, and tire/wheel size, etc. It may be better to have front/rear air pressures vary. Further, there has been no conclusive research that shows that even tire pressures across have any effect on mileage. What does matter is under-inflation. More tire surface on the ground means higher rolling resistance.
Regarding #1, if you want to do this, make sure to note the temperature when filling, and always fill to where you can see the fuel. Otherwise you can see a difference of a couple gallons of gasoline which will throw your measurements all off.
Furthermore, due to variances among stocks and rotation, energy content and quality of gasoline varies from tank to tank, resulting in as much as 15% variance in fuel economy with no changes to driving or other conditions.
And as far as MPG based on speed, this is also not useful or generic enough to hold true. A vehicle's best MPG/MPH will depend on it's gearing. A vehicle that is geared to run at a lower RPM at 65MPH will get better economy than that same car geared to run lower at 55MPH, all else equal. For example, in my 6-speed I will get better economy in top gear at 65 than I do in 5th gear at 55. That means some cars or trucks may get better economy at 70 in high gear than 65 in a lower gear. For example, my Vette gets upper 40's on the freeway at 55 MG in top gear, but if a hill shows up that is not a short one, I am usually better off MPG-wise to drop to 5th than to let it lug at a lower speed in a higher gear.
The single best thing you can do to get better economy in your vehicle is to learn to drive it under it's better conditions, and use the brakes as little as possible. That and don't drive in the rain (as much as 20% reduction). Modern "accelerate by wire" vehicles can see gains of 2-3 MPG across the board by learning where to rest the pedal when not accelerating.

Ucntcme 04:29, 5 November 2007 (UTC)

--- Cheap Savings: 1. Buy a more efficient USED car. Your outlay will be far, far less than buying one new, and may even be worth it in only a year, maybe two depending on how much more efficient it is and what the price is. Of course, this one is quite variable by country; I understand the used market in the US offers far less of a saving than in the UK, for example... overall, at least in my position (living in Britain, not trying to out-bling or particularly impress anyone or win races, just survive within a limited budget), running what is now a 9-year old car makes a hell of a lot of sense, and if I can afford it on less than £14k a year, it's probably chicken feed to someone with the ready cash to consider replacing a perfectly good but slightly inefficient vehicle with a BRAND NEW one (spending several thousand in the process) on the basis of manufacturer's overinflated economy claims...

(current car cost me £2250 in january 05, quite near to the bottom of it's depreciation curve as it's a nice model ... servicing and maintenance costs about £1000 so far... no more complaints with it than a friend has with her from-new £14000 car bought jan 06 (that's not 'none', but it IS 'minimal')... in fact why buy new at all in this day and age of super endurable vehicles? Particularly if efficiency and money saving are your aim? and environment saving, as this way, you're taking ownership of something that's already been built, rather than made especially for you...)

2. Take your normal long distance / fast road driving speed and knock 5mph off it, whatever it is, if it's above 50-55 already. You probably won't notice a significant increase in driving time unless you're going a LONG way; you'll make a small but real saving in consumed fuel just from the steady speed, will work the engine less to maintain it uphill or to reach it after being forced to slow for any reason, and will spend more time in the slower lanes where you'll be less tempted to go even faster than your previous set speed because there's only the open road ahead of you, or to more quickly pull into a gap in said slower lane to move out of the way of a tailgating psychopath. Plus there's less wear on the engine, tyres, brakes and bearings, more reaction time and braking distance to avoid an accident (so long as you don't tailgate - 'drafting' trucks at 55 is a whole different issue, for the truly cash strapped and gung-ho), and less chance of a speeding ticket.

As noted earlier, this blanket statement can lead to an increase in gas usage depending on the car/truck used and its gearing. There is nothing magical about speed. if you car is geared for 55 (older cars), the dropping to 50 can increase consumption. If it is geared for 65 (newer cars), then you likely will increase consumption. Also the comment about hills is so far off base it is astonishing. Maintaining speed up hills is a matter of sustaining motion, specifically momentum. A vehicle traveling at 65 has more momentum than one at 55. Thus, you are better off to start with more momentum up the hill. This is especially true for straight gasoline engines as they lose efficiency under load (E85 and diesel do not suffer this problem anywhere near as bad). Further, speeding tickets have no bearing on fuel economy. Ucntcme 04:29, 5 November 2007 (UTC)

I do sometimes wonder if the so-called speeding 'problem' would largely vanish overnight if government safety agencies would stop agressively promoting the fairly disprovable dangers of it mainly to those to whom it doesn't actually apply (moderate to fast safe drivers and very slow to moderate unsafe ones) or just don't care (fast to very fast unsafe, often unlicensed or antisocial/sociopathic drivers), most of whom will never see let alone be involved in a fatal accident in their lives, and used the same TV and newspaper ad slots and roadside hoardings to just point out the financial benefits in plain terms... something everyone can relate to. - Tahrey 13/1/07

Guaranteed way to eliminate a "speeding" problem: eliminate the crime of speeding. Seriously. It's an obvious point. May not be the best way to go for some, but the reality of it is that it would in fact eliminate speeding tickets. Ucntcme 04:29, 5 November 2007 (UTC)
9 and 10, beginning in the late 1970's there was a shift away from heavy and inefficient AC compressors that looked like lawnmower engines to smaller and more efficient types that use much less horsepower. Except for cars with the tiniest 3 and 4 cylinder engines put into cars too heavy for them, air conditioning has little to no impact on MPG. For vehicles where top gear is a 1:1 ratio, that's the most efficient gear, getting there as quickly as possible without 'lugging' the engine is the most efficient. A large part of the reason the EPA 'city' MPG is less is due to so much time spent in the lower gears, the other is time spent idling at stop lights and signs. If the transmission has an overdrive gear (where the driveshaft in RWD or the last gear before the differential in FWD is turning faster than the engine) that is the most efficient gear. For used cars, especially Ford and GM RWD models, it's often possible to swap a non-overdrive transmission for one with an overdrive. Unfortunately for Mopar lovers, they never made a RWD automatic with an overdrive (I dunno if they did manuals with overdrive). The easiest ones are before computer controlled transmissions, but even the "E" versions can be swapped, there are companies that sell reprogrammed computers for that. —Preceding unsigned comment added by Bizzybody (talkcontribs) 04:07, 4 September 2008 (UTC)

I appolize for whatever ineptitude[edit]

Preliminary apology:

I apologize for the Wikipedia ineptitude displayed. This is the first time I have been here. I don’t know how to do this.

I found this on Wikipedia:

"Avoid driving at excessively low or high speeds. Most gasoline powered cars operate with maximum efficiency in the range of 45 to 60 mph ( 70 to 100 km/h ). This effect is largely due to aerodynamic drag. For vehicles with greater frontal area and less streamlined shapes (SUVs, trucks) best fuel economy is typically obtained toward the lower end of this range."


I think the above is garbage I am a mechanical engineer. I have some experience with automobiles, and I have driven one for many years. Who writes this stuff? Where is their data or theory? How can it get changed?

What does "maximum efficiency" mean? Is that distance per unit of fuel or is it distance per dollar including driver time and "My time ain't cheap?"

I think this is stuff written to justify wacko driving. unsigned comment by Ecar 12:43, 23 September 2005

Check out What speed should I drive to get maximum fuel efficiency? --Ben 03:26, 29 November 2005 (UTC)

re: Ecar ... explain your 'wacko driving' comment? You mean anyone who drives slower than you wish to, I assume, rather than the other more extreme/potentially dangerous examples on here of e.g. 'slingshotting' (or pulse-and-glide). I too get frustrated at slow drivers on fast roads (particularly when there's very limited opportunity to get past them), but the full force of my ire is now saved for the truly slow ones (35mph or less) once I did some bottom-dollar essential driving at low speeds and was surprised at how long each precious gallon lasted, and did some (rather unscientific and unrepeated, but eye opening) testing later when I had spare cash and time. I now know those doing 40 to 55 are as likely to just be poor or economy/environmentally minded rather than lobotomised... the amount of fuel I DIDN'T use travelling a 50-ish mile test route at a steady 45mph was incredible, certainly compared to how much it would have been at 75, or even 60. I achieved something in the region of 70mpg... or nearly double what I usually managed tearing around the same stretch at 75 to 90mph... that, and similar receipts (more reliable, as greater distances were covered - on the 45mph run I barely consumed a typical gas station's minimum vend amount) for figures such as 66mpg at around 50, 59 at 55mph, etc suggest there's considerable weight to this argument, and not just the ravings of some tree-hugging nut jobs. Whether your time is more valuable than the fuel you're pumping into your car or the CO2 you're conceptually pumping out of it is a matter for your own consideration. Presently, I'd love to be getting probably 60mpg out of my slightly thirstier 'new' vehicle under a similarly disciplined regieme, but I just don't have the spare time in my life or the ability to deal with the stress that would be directed towards me for it, when I can fairly easily afford to use an extra half gallon every 40 miles. Besides, a lot of my driving is in cities rather than on the open road; in the urban area it's all you can do to try and brake early and gently to try and avoid unneccessary downshifts and stops (as pulling away from a standstill and sitting idling are big wasters) and condition yourself to use 50% throttle and the highest possible gear, as your potential maximum speed and even your ability to accelerate with any force is severely limited by lower posted limits, the terrain, and other drivers being dopey and frustratingly/inefficiently slow :) (Now, if the only available car could only manage 15-20mpg at 70mph, rather than 35-40, my long-distance speed choice might swing the other way... and i'd cycle across town even in the rain) -tahrey 13/1/07

Fuel Economy Trends[edit]

I think it would be good to work information about fuel economy trends into the article. Here's some stuff I found so far:

--Ben 03:26, 29 November 2005 (UTC)

What about the USArmy's Multi-fuel engine? it will riun on whatever u put in it...even water but don't go looking for any great numbers...

Thermodynamics 101[edit]

This page is really misleading and tries to express engineering principles and laymans terms. To summarise:

Fuel efficiency is simply useful energy output divided by heat or chemical energy input expressed as a percentage. This can be calculated for any thermal plant e.g. power stations IC engines etc. It is affected by a number of factors depending on the thermal cycle and machinery used.

Depending on which camp you're in, fuel economy is the amount of fuel required to go a fixed distance (l/100km) or the distance which may be travelled for a fixed amount of fuel (mpg).

Specific output is the power output per unit displacement.

These there measures are separate and NOT related! However, factors which affect one measure may well affect another.

The efficiency page needs to be totally re-written so that it contains actual facts.

Yotboy. 192.149.117.69 13:25, 2 January 2006 (UTC)

Section: Fuel Economy[edit]

Added external link to text "93/116/EC"

... European Community Directive 93/116/EC.

-Mardus 11:38, 8 January 2006 (UTC)

For article translators: The Directive is also available in other languages in here.
-Mardus 13:37, 8 January 2006 (UTC)

Section: External Links[edit]

  • Separated links that take to sites/pages commissioned by various governments' institutions
I wasn't quite sure as to how necessary it was, but since I noticed that they could be grouped like that, then I thought, why not, and one of the reasons would be that the number of links was such that like links could be grouped together.
Only that I grouped them into sections, which immediately reflected in the Contents bar at the top of the page, as a very long section title significantly extended the Contents bar's width. So I changed code to remove sections, but keep the whole section's appearance.
  • Wording...
Added the above link (in "Section: Fuel Economy") to External Links section, with a link description (which is the title of the directive) referring to another directive, which I also linked, but didn't place to a separate line, perhaps for the sake of brevity.
The link looks like this:
— The problem there is repeated text "European Community Directive 93/116/EC" and "European Commission Directive 93/116/EC" and that extends the whole area containing the link and its description.
I would delete "European Commission Directive" part placed after the link, but I am not sure then as to the wording of the actual link, as section Fuel Economy contains reference to "European Community directive", while the actual directive says it's a "European Commission Directive" in its text.
The question boils down then (if the repeated part were deleted) to whether the Directive would be referred to as a "..Community Directive" or a "Commission Directive".

-Mardus 12:20, 8 January 2006 (UTC)

article expansion[edit]

This article could be usefully expanded - it shouldn't just be about cars. Interesting questions are: Why are some engines more efficient than others? How do different types of engines compare (Deisel, Fuel Cell, electric, etc)? How do cars compare with aeroplanes, ships, rockets, steam engines, human body, etc for efficiency? How (in detail) has the efficiency of engines improved over the centuries?

There should also be short introductions and links to topics like aerodynamics as it pertains to fuel efficiency. This article is not a specialised topic and should be in layman's terms. I imagine that, with energy issues being so in the news lately, a lot of people will come looking for information on fuel efficiency. Seabhcán 11:17, 2 February 2006 (UTC)

Perhaps it would be better to restrict the comparation to modes of passenger transportation from one point to another of the Earth surface. Comparison with the Space Shuttle is meaningless. Also it's not fair to compare cars with humans (either walking or cycling) because the form of energy they use is not interchangeable. StefanoC 12:43, 23 February 2006 (UTC)

article splitting[edit]

I don't see why this article should be exclusively about fuel efficiency of vehicles. The concept of fuel efficiency applies to any machine which does work. A section on power stations would also be useful. I added the trivia on the space shuttle and humans because it's interesting. Yes, food energy is not interchangable with gasoline. But equally gasoline is not interchangable with diesel or hydrogen. Seabhcán 15:20, 23 February 2006 (UTC)

As it is, the article talks mainly about the fuel efficiency of cars. Maybe most of that discussion should be split to a different article: Fuel efficiency of vehicles perhaps ? StefanoC 15:34, 23 February 2006 (UTC)
Yes, That sounds like a good solution. How about Fuel economy in automobiles?, to distinguish it from the slightly different concept of fuel efficiency. Seabhcán 15:41, 23 February 2006 (UTC)
Split request posted into the article. Are there deadlines for the discussion ? StefanoC 08:12, 24 February 2006 (UTC)
The current article focuses almost entirely on gasoline-powered cars, although the nr. one reason for buying diesel-powered cars is fuel economy. I suggest naming the new article Fuel economy of gasoline vehicles. This allows new types of fuel to be inserted, i.e. electrical, vegetable oil, hybrid, diesel. These fuels may have characteristics which are not shared with other types of fuel, regarding economy.

Vehicle Fuel Consumption - Volumetric Efficiency[edit]

Many years ago a British car magazine set up an economy test to verify the theory that petrol (gasoline) engines are at their most efficient with the throttle open during brisk acceleration. A Jaguar car was driven for a predetermined distance at a moderate constant speed on a closed test track, the speed chosen being the most economical for that vehicle. Mpg results were noted. The test was then repeated using the "slingshot" technique, accelerating strongly to a speed well above the constant speed on the previous trip, followed by switching off & coasting in neutral down to a very low speed, then repeating the acceleration/coasting, until the set distance had been covered in approximately the same time. The result, as you have probably guessed by now, was a conclusive win for the slingshot technique. This result appears bizarre & counter-intuitive to the average motorist, who assumes that moderate constant speeds are best. I can't remember the name of the magazine, and I'm trying to find further information on this topic; can anybody help?

I don't know the mag/etc, but this makes sense. When you do not drive at full power, there is a metal plate, the throttle, placed into the airflow into the cylinders. This creates quite a bit of stoppage that the pistons must overcome in order to draw air into themselves. At idle it's about 50% of all the fuel burned, at typical cruise speeds 15%, and at "full out", 0%. So basically if the engine is run at full power, one source of drag "goes away".
However this also covers up another issue, air drag. At hiway speeds the majority of the drag is from air resistance (I believe, the crossover point on a bicycle is 12 mph, so it's likely not THAT much higher for a car, 30 mph perhaps?). Drag from air resistance goes with r^2, so as the speed increases, the drag goes up even faster. So my guess is that they did this test at low speeds, ie, slingshotting on either side of 30 mph for instance, as opposed to 60 mph. My guess is that at a hiway speed the throttle drag losses would be much lower than the air drag losses when you slingshotted up to 75 or so.
Maury 22:48, 7 March 2006 (UTC)

This test, while pointless, makes complete sense when you estimate & compare the average RPM levels of the two cases. They just misconstrue "efficiency." In the first test, the engine runs at a constant but moderate RPM for the whole test, resulting in a high average RPM. In the other test, the RPMs spike to get the car to a high speed, and then the RPMs drop to neutral while the car coasts "to a very low speed." Repeat that process for the whole test. This would result in a low average RPM, and less fuel used. This is already common knowledge.

FattyArbuckle 28 April 2006

I think it might be illustrative to think of it as extracting more power from the engine, and the fuel, whilst making more of a saving against internal friction from the engine (as it's being run at a lower average rpm, only going higher than that of the continuous-speed car for a small proportion of the time, and may well be turned off completely for a similar or longer period) than is potentially lost to wind resistance due to going faster (but then - you'll make a saving THERE when going slower also). This works particularly well if the slingshot car remains in top gear and accelerates on more efficient mid-range torque than going all-out at high rpms. As I noted some time ago at the bottom of this thread :) it's similar to the technique used in 'true' hybrids, particularly at low speeds in town, where frictional and throttling losses in the petrochemical engine are immense compared to wind resistance (which makes high speed running inefficient for any type of propulsion, but is negligble below 30mph, ironically the point where most ICE vehicles will HAVE to downshift to avoid labouring), allowing them to famously make a killing by running on all-electric power, only kicking the oil-burner into relatively wide-throttle life for a short period when the (often laughably low-capacity, but acceptable for THIS purpose) batteries drop below a certain level of charge. Unfortunately, because of the assumptions built into most carburettors and vacuum advance systems, and programmed into their modern equivalents regarding what a driver is doing according to the throttle pedal setting, a variation on this method - giving a car about as high a top gear as the engine can sustain at moderate highway speeds - doesn't work well in practice. Even though it drops the RPMs (further) into the efficient running zone, the carb/vac or ECU interprets the 90-100% wide throttle as 'accelerating hard' or 'climbing a hill', and the resultant enrichment of the fuel mix and timing alterations (maximising total power output, but not output per consumed unit volume of fuel) negates the saving from lower RPM, higher torque and less throttling loss rather than adding to it, particularly as this is now the steady state rather than a blip. (Despite someone with better engineering knowledge than me arguing against it, I did once fit a slightly underpowered car with the turbo variant's gearbox, thinking - with the backup of a careful mathematical check - it would improve the cruising mpg still further from the standard... though it was a fair bit quieter and more comfortable, the consumption remained much the same and possibly decreased, given that full throttle now only sustained about 75-80mph in top instead of 90). It does however seem to work well for diesel engines, probably explaining some of their efficiency (lower rpms, better torque but similar or less power meaning a wider throttle setting, and less obstruction to the inlet path as the fuel is injected directly to the cylinder or inlet manifold rather than in an identifiable throttle body) ... I guess their fueling setup must be administered differently, and of course, there's no ignition to advance or retard... (also it did the business for the Insight, which had higher gears on it's 1.0L + occasional electric boost engine than my 'economy' 1.6L has - Honda must have reprogrammed it quite comprehensively) ... Hmm, that gives me an idea for a different yet similar project with a diesel and a scrap lift winch motor, when I once more have the time and money :D - Tahrey 13/1/07

Average European Car[edit]

How come only European subcompacts are mentioned. Less than 18% of cars in Germany are subcomapcts, so shouldn't the fuel economy for the average Euro Car, such as a Passat Diesel, be added to the page. It seem rather POV to compare a subcompact to an Impala and an Expedition. Thanks for contributing. Gerdbrendel 18:38, 10 February 2006 (UTC)

It is a strange imbalance, but I would like more exposition from that bank of information you seem to be drawing on.. very few people I know drive Passat-sized cars, and when they do it's usually for a good reason (having to carry numbers of tall adults or bulky cargo around, high performance, professional image, overinflated ego, all they could afford in the bargain-bin second-hand lot).. So-called 'Sub-compact' and the slightly larger supermini (i suppose 'compact'?) models are hugely popular in europe for reasons of practicality, style, cost of purchase/ownership/fuel, handling and maneuvrability, possibility of moderately high performance with quite small engines, etc. If only 18% of Germans have a subcompact (possibly because the pool of available models has badly dried up - no more Seicento or Lupo, for a start!), is it maybe because a much larger proportion have a 'plain' compact?
Thinking over everyone I know, I can probably name a maximum of four people who have what would even count as 'mid size' in the states (Mondeo/Passat size).
My uncle carries a lot of gear, and often a lot of large bodied people for his job as a building site supervisor (Mondeo)
A friend of mine has been gifted his parents' old 1.8L Mondeo to replace his spectacularly corroded old Escort (they've bought a Focus instead)
One of my mother's friends has a Saab 93, as he has a high-paying job and likes a bit of luxury, but is more often seen outside of business hours driving about in his daughter's Renault Clio because it uses far less fuel and is easier to handle
...And my father is a borderline case, having traded in one mid size station wagon (Volvo 240) and a compact-midsize genre straddler (Citroen Xantia) for another one (Honda Accord) and a comically small delivery van (Daihatsu Hijet) as both of the old ones were falling apart and way too thirsty - the new vehicles slightly less so in both areas, and more suited to the self-employed craft deliveries he makes (one car for business, one for personal use, rather than two mixed-use ones) within a shoestring budget (under £2000 overall, including money from the sale of the old jalopies).
Everyone else? Superminis or subcompacts - mainly superminis. The interior room and access and general performance is more than adequate for 99.5% of situations they're called on to meet, they're affordably efficient and, if you're buying new, cost far less (used prices, not so much difference - but in that way there's far less depreciation loss from new, too), handle well and are easy to park. True 'mini' cars are cheaper still and even more efficient and city-friendly, but tend to sacrifice too much to achieve this than is generally acceptable. Perhaps the article focus is in the wrong place - but only slightly. -Tahrey 13/1/07

This is not wikibooks[edit]

Please keep it to third person. The idea is to inform the reader, not tell the reader what to do. That's Wikibooks' job. Elle vécut heureuse à jamais (Be eudaimonic!) 05:20, 13 February 2006 (UTC)

Ummm, is this actually right?[edit]

Naturally aspirated engines tend to be more fuel efficient than engines with forced induction (ex: turbocharged, supercharged).

From the little thermodynamics and engine theory I know, this statement seems incorrect. Turbochargers use waste energy in the exhaust to presurize the intake, thereby overcoming throttling losses (which are about 15% at cruise power). Whereas in a normally aspirated engine the pistons have to suck air into the cylinders, using up real power, a turbocharged version of the same engine would have no losses to this suction, and get that energy for free.

Can someone illuminate?

Maury 22:42, 7 March 2006 (UTC)

Only by example, a friend of mine wanted to fit a turbocharger to his car then decided against it because the fuel economy would be too costly for him. ( ok the excitement working for a racing team went to his head!) So from that I guess it must be true. Someone else can explain the theory, I should think it has to do with 'backpressure' config.

---


This is another one for those arguing volumetric vs thermal efficiency, or whatever it was. The turbocharged car drags more useful power from the engine (same displacement, more grunt) and the fuel (using more juice, but producing disproportionately more push from its combustion), but tends to get used for more inefficient uses (high speed running, WOT acceleration etc) and suffers other inefficiencies that can hurt it in normal use (particularly in town) or when idling (lower compression ratio when off boost, higher compressive friction when on it, altered fuelling and ignition maps, using more fuel to satisfy lambda requirements coming from more air entering the cylinders etc)... not to mention the drag from the turbine itself and the longer intake path, particularly if an intercooler is used.

(BTW your missing part in the air movements part is the drag felt by the cylinders as they push the exhaust out through the port... though there's not too much of it as it's mainly decompressing having been heated to several hundred degrees, it's still got some backpressure effect from the vanes of the exhaust turbine)

Unless it's offering a spectacular amount of boost, the overall economy cost isn't so great - though it is noticable - and the effects resulting from it could be described as 'worth it' :)


(More consisely (sp?) - it makes the original engine less efficient overall and is detrimental for light duty applications, but improves the amount of work done per volume of fuel under load)


Examples: 1272cc Volkswagen MPi engine, non-boosted version puts out 75hp; boosted G40 variant (technically supercharged, but subject to similar arguments) gives 113hp and similarly increased torque from essentially the same components, but with a thicker head gasket, altered ECU map and a compressor. On-the-road performance is noticably increased, and when being driven hard doesn't eat *too* much fuel (though it's still not exactly wallet or eco friendly!), and is certainly competitive in this area with larger displacement unboosted engines - but it does lose a few MPG compared with the NA model when cruising at legal speeds and has definitely unenviable (for a 1.3...) economy across town.

On the other hand, I have heard of caravan owners who have justified fitting turbos to their saloon cars to their insurers as safety and economy improvements to the vehicle, allowing them to pull onto busy roads more briskly and traverse inclines at higher steady speeds (with less danger from overtakers and less risk of overheating the engine at high rpms) without having to invest in a different, possibly larger/more prestigious (and therefore more expensive to buy and run) vehicle with an inherently meatier and drastically more thirsty engine. Again the arguments are a bit moot when cruising with/without trailer around town or at steady highway speeds on flat ground (the turbo in this case requiring the RV's justification to be more than a tyre-spinning toy :), but the device comes into it's own when sustained high power is required, helping the user tour more efficiently and swiftly without using a bigger and (comparitively) inherently less efficient engine.

... and not for nothing is the Turbo Diesel the powerplant of choice for those who haul big loads for a living (truckers, bus and van drivers, etc), with the non-turbo variation being largely forgotten except for those seeking ultimate economy (with performance a very distant second priority) in smaller vehicles.

I don't need one myself, I don't drag large weights about and can already go as fast as I presently dare to (90~100mph depending on gradient) without either a big engine, a compressor, or even running WOT more than 50% of the time, so the fact of it making larger power outputs more cost effective is neither here nor there.

Clarifications, edits, what have you, from people who actually know anything about this rather than relaying other things they've been told or have read and adding educated guesses, would be most welcome.

--- tahrey (i will eat this thread hehe... i must get off the net i think) 18/4/07

Efficiency of rockets[edit]

It's not fair to compare the miles/gallon of the Space Shuttle with those of cars and trains (that don't have to work against gravity). One more meaningful measure would be fuel consumption vs. potential and kinetic energy gained. StefanoC 08:45, 13 March 2006 (UTC)

I added it more as a piece of trivia, rather than a serious comparison. Seabhcán 10:57, 13 March 2006 (UTC)
Yet it could be interesting to show how much (in)efficient rockets are with respect to other engines or to, e.g. a Space elevator StefanoC 13:15, 13 March 2006 (UTC)

accuracy tag[edit]

Fuel efficiency is not expressed in terms of power per unit of engine displacement. Meggar 01:09, 5 April 2006 (UTC)

That section should be substituted perhaps with a discussion of theorical limits (Carnot efficiency) and a general description of the relative efficiency of open vs. closed cycles, otto vs. diesel, gas vs. steam. StefanoC 14:42, 5 April 2006 (UTC)
Yes, that is what should be here. The entire paragraph starting with the premise is incorrect. Deleted. Meggar 02:27, 23 May 2006 (UTC)

merge with Fuel economy in automobiles?[edit]

There has been no comment on this on either page in the month since the tag was put up. Here is one for Oppose. PS, tag removed by another user. Meggar 01:48, 27 July 2006 (UTC)

what the?[edit]

Do my eyes deceive me or does that final table seriously suggest that, on average, private cars and motorbikes are the most efficient forms of transport? Either there's some revolutionary idea in there, public transport in the USA is BADLY undersubscribed, or someone's paying off the DOT's research division... Also, regarding the "slingshot" idea - this is why, in part, hybrids can get better economy, as in an ideal situation the mean power output would be the same, but the gas engine would only be used to charge up the batteries, running at a low and efficient rpm with near- or completely-wide open throttle for minimal losses (kept at the lower speed by the load from the regenerator), with all running power coming from the electric motor alone; the gas engine turning on only when the batteries start running low, and turning off again once they're topped up. Obviously that's more for the DIY feats of engineering than a current road car, as the battery packs (and electric motor specs) are laughable and the control systems are not aimed at this end. However a variant on the slingshot technique known as "pulse and glide" has been known to help economy amongst Prius drivers - it takes advantage of certain distinct motor-on and off points and system reactions to user input to deliver noticably greater fuel economy with an average speed of around 35mph ("pulsing" up to about 40 with the motor at fairly wide throttle, and "gliding" back down to about 30 with either zero power, or only the electric motor being turned on). Obviously it's not a good idea for safety or road manners, and it can be argued that a large part of your economy comes from forcing yourself to run at only about 35mph (which, certainly amongst some uk workers in low paid jobs (ahem - NOT only myself), is a recognised method of squeezing the last few drops in the tank that little bit further until payday/the filling station)..... but its certainly an interesting technical case in point.

Experimenting with my current car - 1.6 SPi Opel/Vauxhall Astra (Pontiac Le Mans) 1998 - I've found the only way to maintain fuel economy is not to rush around and to drive calmly. There's not much I can do to it to "improve" it even with coasting etc.. it's just an inefficient design! ...however it IS the most efficient inamongst its immediate family and peers, including some with 1300, 1400 or 1500cc engines and full multi-point injection. A smart focus on making the engine torquey (and therefore very responsive and effortlessly accelerative at low speeds) rather than ultimately powerful (something rarely actually required of a general use road car; it's "weak" 69bhp is still more than adequate for 110mph) means the driver doesn't waste fuel revving it into the higher ranges to pull it from a standstill, even though it is mated to a high range gearbox (another good blow for economy - it revs lower at intra/intercity and cross-country highway speeds than most, sitting nicely in the torque range with just a very slightly wider throttle setting). Too bad the metalwork of the engine itself is stone-age, and the body is heavy, wide, and although sleek, not super aerodynamic. Hybridisation is a nice idea, but it won't solve all problems - now that we're finding clever ways to make a normal sized car seem enormous internally, the exterior size needs to come down, along with the weight (and the shape made more aerodynamic, like an insight or calibra), and the engines built - rather than programmed and tuned - as lightly and efficiently as possible (including making the capacity a whole lot lower and dropping the current resurgence in bhp-figure obsession), if not altogether removed in favour of electrification.

Removal of properly referenced data[edit]

For some reason, Eric Kvaalen (talk · contribs) has removed the fully referenced data in the energy content table and replaced some of it with less reliable online sourced information. This has also left some parts of the table entirely empty. The fact that he doesn't personally have access to the industry standard reference manual from which the data was taken does not justify removing data that wiki, by definition, considers more reliable. I haven't reverted his edit this time, but I do believe that it is actions such as his that undermine the fundamental validity of wikipedia. --Athol Mullen 21:17, 9 March 2007 (UTC)

  • It's about 7 weeks on and the vandalised data table remains in place... --Athol Mullen 02:17, 28 April 2007 (UTC)

The RON number minimum for regular unleaded fuel is much higher than the minimum. The minimum I've seen in several states is 87. Someone able to justify the 91 octane number being "minimum"? Ucntcme 03:19, 5 November 2007 (UTC)

In UK / Europe the RON numbers are different again. For the UK, regular unleaded is 95 RON and super unleaded is 98 RON (although that is much rarer in recent years). Warmington (talk) 13:36, 10 November 2011 (UTC)

Other trains[edit]

The C-Train in Calgary, Alberta, Canada is entirely offset by a wind farm south of the city. —Preceding unsigned comment added by 208.38.1.1 (talk) 20:33, 18 September 2007 (UTC)


Diesel Vs. Gasoline[edit]

To me the article implies that the increase in energy content is responsible for the majority of economy differences between gas and diesel. The clear dominant factor is the 50% better efficiency - extracting more energy from the source material. Clearly, 10% more energy in the fuel can not produce a 40% increase in economy, but getting half again as much out of the fuel certainly can. Anyone up for improving the wording there, or shall I? Ucntcme —Preceding comment was added at 04:35, 5 November 2007 (UTC)

Fuel Economy infobox[edit]

In a related matter, does anyone think that fuel economy should be kept out of the automobile infoboxes? Please voice your opinion at http://en.wikipedia.org/wiki/Template_talk:Infobox_Automobile#Vote_on_Fuel_Economy_in_the_Infobox 198.151.13.8 (talk) 18:28, 7 May 2008 (UTC)

CCPP and electric drive outperforms any ICE in efficiency[edit]

CCPP with natural gas have 58% efficiency in electric power production. New planed CCPP should even exceed 60%. The only car known by me in all versions is the Renault Kangoo. Here a study about the efficincy with gasoline, diesel, natural gas and electric power version Cleanova 2. --Pege.founder (talk) 10:19, 30 May 2008 (UTC)

E85?[edit]

Why haven't the numbers for E85 (85% Ethanol, 15% gasoline) been added to the chart? —Preceding unsigned comment added by Bizzybody (talkcontribs) 04:10, 4 September 2008 (UTC)


Regular Unleaded[edit]

In the UK, and most of Europe, regular unleaded is 95RON. Premium is 97/98/99RON.

Methane as Fuel[edit]

Is there place for methane in the table? According to http://www.littleredbook.com/fuels.html methane has 23,875 Btu/lb —Preceding unsigned comment added by 89.79.66.46 (talk) 09:53, 7 September 2010 (UTC)

Riian.januarianto (talk) 20:43, 20 February 2012 (UTC)

Hybrid Vehicle[edit]

if we talk about the fuel efficiency, what if we discuss a little about the gasoline / diesel fuel combined with electric power and make a hybrid vehicle.