Graph of Engine RPM vs MPG

Thanks PWS, now that i know what i am looking for i should find it..

She is a diesel, Vauxhall Insignia i brought in from Scotland. The previous car was a 1.6 petrol Vectra and was very had on fuel and the wallet. Thanks for the additional info improving the MPG. Appreciate it.

just to add to the discussion. I did a brief study a couple of years ago when I was considering a hybrid. all the mileage claims are great for marketing but if you read some of the un-bias reports by owners a year or two after purchase you consistently find in the real world the hype doesn't quite always deliver. then factor in the actual dollar savings per gallon of gas and subtract that from the premium being paid on the initial purchase and what I found was the hybrids in most cases were not a better deal over high MPG base models without all the expensive tech. if you also consider that future service of any type sends you back to the dealer Only the hybrid doesn't always make he best choice. so keep your foot out of it and do your regular maint.

Fredski, I also did an analysis of hybrid vs non-hybrid and my conclusion was that the difference in price could be offset by the fuel cost. Since we don't have many high mileage diesels here in California, the best comparison I could come up with was a Prius vs a Corolla. I calculated the monthly payment of a Prius vs Corolla (similarly equipped), then chose different gas prices and found the break even mileage per year. It's obvious that as gas prices rise, the break even point gets lower, but I was very surprised to find that at $4.50 per gallon, the break even point was about 24,000 miles per year. At $5.00 per gallon it's 21,500 miles per year. At $5.50/gallon, it's 19,500 miles per year.

And don't kid yourself; gas may not be at $5/gal yet, but it's coming. We've been printing so much money that our dollar must buy less (more dollars with the same amount of goods). After $5/gal comes $6. We're now happy if gas gets below $4/gal now!

I for one don't care how much it would save me but I would never ever want to drive 24,000 miles a year in a Prius.

I did one long distance trip in one a few years ago and that was enough for me to never want one no matter what it would save me money wise. I also found that if you drive a Prius like you drive a normal car they basically get the same MPG numbers but with the disappointment of having far less power especially once the battery runs down.

My experience with driving a Prius

They might save you money on fuel around town but I would hate to try and put in 24,000 miles a year in just in town driving.

By the numbers they may sound good but in applied reality not so much.

TCM, I have driven many Prius cars - never owned one though, and sure, if driven hard, they get fair gas mileage. But a Corolla driven hard will do the same. And ditto for and other econobox. If you want to push a Prius to an inefficient state, you know what the gas mileage will be. What does a Prius top out at? 99 mph or so? So at 85+ mph, you're really pushing the car (I'm assuming you drive around 85 or more, because you sound like you're a spirited driver - so am I). Add a hill and a/c and I can see mpg in the 30's. But this is not what the car was designed for.

Okay, here's an analogy. If you buy a pair of Klein pliers, they'll last a lifetime, however for an average homeowner, it's overkill. So why spend $50 on pliers, when a $20 pair of Craftsman will do the trick? Now if you're an electrician, you'll obviously choose the Klein's. The tool is designed for a certain user and a task.

Same for the Prius. The Prius is a commuter car that is not meant to be a high speed highway cruiser. Nor is it meant to be driven with your foot the the floor as the light turns green. If you want strong acceleration, why on earth would you buy a Prius? If you want to cruise at 85+ mph on the freeway, I ask the same question.

This is why a Prius doesn't work for me. When I get one for a client, I'm not going to floor the gas or drive at anything above 70 mph. It's not my car and I don't think they would appreciate it. When I jump in my car, it's a different story.

To summarize, the Prius is an exceptional car for people who want/need high gas mileage. If you drive agressively, don't buy a Prius or you'll be disappointed. One last point; the latest generation Prius has been updated and it makes the last gen feel old and dated. The new one is also much more fuel efficient and isn't affected by cross wind as much. And the first gen! Fuggetaboutit!

Thanks for sharing and this was a good discussion.

Personally I don't consider it a good vehicle unless it can carry 6 people who are 6+ feet tall and 350+ pounds and pull at least it's own weight at typical interstate speeds of 75 - 89 MPH and still not have the gas pedal flat to the floor.

Now relating to the drive WOT then coast concept that doesn't work that well on a vehicle with a real engine either.

Try doing that in my old 1985 Ford F150 pickup that had a 400 HP engine that pushed 500+ Ft/lb of torque at 2000 RPM.

Well okay the coast part worked just fine. Granted when I was pulling twice its own weight the coasting part was the most fun being it had headers and dual independant exhaust with 36" glasspacks. Drop it down into second gear at 70 MPH watch the RPM's hit about 4200 and listen to the pipes crack and pop for the next half a mile!

(Josh I miss that pickup now.)

You guys have it good! Back when I was in college, my friends and I took my 1980 Camaro and put bigger heads (with bigger valves), a tall intake manifold, Holly 650 cfm carb, tall - long duration cam, stall converter, headers, free flow mufflers (not glass packs - my parents and neighbors would've killed me) and a new higher ratio posi rear end! Of course, the smog was yanked out - you know, who needs all that weight! It was such a fun car, but I couldn't get it over 135 mph - too many revs due to the rear end!

Here in So Cal, we can't do stuff like that. When your car gets to be six years old, you have to take it in for a smog check every two years. It's a visual inspection and a tail pipe emissions test on a dyno (unless it's awd). No more paying off the smog guy - the risk isn't worth the few hundred dollars for him. So, everything I own has to pass smog.

A couple years ago, I had a Porsche 996 (911) coupe that had a free flow exhaust (pipes and muffler), intake, short throw shifter, chip, slightly lowered with shorter springs and suspension components, rear wheel spacers and 275 width rear tires (265 was stock). That was the quickest car I've ever owned and by far the most fun to drive. My guess, it was pushing 325 hp with a bit over 3,000 lbs of weight. 0-60 was in the 4.8 sec range. I never topped it out, but I did hit 154 and it was still pulling strong - I'm guessing it was a 180 mph car. I had to sell my baby, due to too many tickets in a short amount of time (two tickets in a six month period in my (986) Boxster 2.7L with an auto trans - zero tickets in my 996 - go figure).

Since I know I can't behave, I have to drive "reasonable" cars. No more fast sports cars - I can't afford the tickets!

Whee! What an exciting ride!

Nice real world reference!

Thanks for the recollection.

By any chance, do you remember what mileage was achieved to win the competition?

However, that's not the whole deal. There's more things to consider:

• Compare the meerkats on insurance
• Consider low-mileage high-age vehicles rather than new ones so as to reduce both the capital employed and the loss of interest on it
• Look carefully at the depreciation rate and select according to vehicle longevity
• Look at economy models so as to reduce the road tax payable as well as maximising the mileage obtainable from a unit of fuel
• Buy privately and at auction rather than from a dealer - especially with previously-enjoyed vehicles
• Consider replacement like-for-like at the end of the vehicle's economic life so as to recover usable parts from it for redeployment on the replacement - batteries, road wheels and tyres/tires, etc. Dismantle and offer the remaining parts on internet auction sites (names withheld) rather than despatching the whole vehicle for recycling as a unit
• Etc., etc.

A graph won't help you. It's the personal traits that drivers have that determine fuel mileage, not some graph, unless you gather the data based on the way you drive, a graph is useless.

Read these instead.↓

How to Get the Best Gas Mileage out of Your Car

How to Increase Fuel Mileage on a Car (with Pictures) - wikiHow

Driving for Maximum Fuel Economy - Henderson Trucking Comp

Lyn,

Graphs are just a convenient way to communicate. The information on the graphs could have been put into words and presented in bullet form, in the way your 1st link did.

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The right information presented in such a way that the audience can (and wants to) understand, whether in short sentence, or in graphs provide drivers who want to improve their efficiency, with the information necessary to change their personal driving traits.

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What is important is not if it arrives in short sentences or if it arrives in graphs. What matters is if the information is good.

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On that point, I like your 2nd and 3rd links. There are a couple questionable things in the 2nd link, common minor misconceptions, but overall it is solid advice.

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But the 1st link you provided... well, it's crap.

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You don't need to take my word for it, you can just reference the other two links you provided, which directly contradict the info in the first link you provided.

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The first two points bulleted in your first link are fairly mild goatfucqs, so we can kind of ease our way into reviewing this train wreck.

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• Try to purchase your gas at the coolest time of day. Gas is densest at these times, so you'll get more out of the volume.....'

That first one makes me wonder if the author things all the gas is somehow squeezed into the above ground box they identify as 'the gas pump'. Fuel is of course stored typically in large underground tanks, which are affected very little by the temperature variations over a single day.

The temperature of the fuel probably varies far more with how recent a tanker truck refilled it. If it is dead of winter, a recently filled underground tanks might be relatively colder than tanks filled long ago, whereas in the heat of summer, a recently filled tank might be less dense than ones that were not filled recently.

Overall that 1st piece of advice fails in its attempt to give advice on a subject they clearly do not understand well.

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• Use your manufacturer's recommended type of motor oil to increase your gas mileage up to 2%.....'

This is a stupid thing to say. Where did they get the '2%' figure? The truth is using the recommended oil could improve your mileage far more than 2% and interestingly there are probably non-recommended oil that would increase fuel economy, in the short term at least.

Moving on to #3:

'.....When starting your car, you don't need to run it for more than 45 seconds. After that, you are just wasting fuel......'

This is moronic. If I only needed to run the engine for 45 seconds, I would have walked.

Now, I'm pretty sure I know what they meant to say, much like I know when my dog has to go outside to leave a dump....but I'm not in the habit of taking advice from my dog either.

Communication is a prerequisite for successful advising.

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Just to note the tally: A total of three crappy suggestions from the first three questions! ( Apparently this website does excel at some things!)

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There are additional problems in that first section labeled 'before your travel' accompanied by some spectacularly bad writing. I encourage anyone interested to peruse the carnage.

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Moving on the the 'Kerouac' 'On the road' section, this piece continues to get high marks for consistency. No time is wasted, the first problem arrives in the very first suggestion:

'...Don't start and stop your engine multiple times. Idling for one minute consumes the same amount of gas as starting your engine....'

This is in direct conflict with information in the other links you provided....

'....Generally, if you can avoid 10 seconds of idling you will save gas by turning the engine off and restarting.....'

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This next one is simply wrong, I suspect someone is just fishing stuff out of their butt to fill this article:

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• When you are approaching a hill or incline, make sure to accelerate before you reach the hill to avoid using excess gas to get the same result ON the hill.....'

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This next one recommends cruise control for highway trips, but if you know how to drive efficiently, you can do far better than cruise control.... that was the intent of this web page right? Well, considering the advice given so far, perhaps suggesting cruise control is the best idea, since no one is going to be a better driver for having reviewed what the fantasized.

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• Use cruise control for highway traveling. .....'

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I really am missing the point on this next one...

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• Avoid reverse driving maneuvers. ....'

...They don't actually think that because your are driving backwards that it counts against your forward miles per gallon, do they? Do you think driving around looking for a spot you don't have to back out of is going to waste more fuel than just backing up?

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And rounding out this spectacular composition.... another outright falsehood!

'....Watch your acceleration! Slow your acceleration time down to 15 seconds (when going from 0-60 mph) and you can save 30% on your gas mileage....'

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A funny thing in one of the other links was the idea of using only 1/4 of your tank of gas. They suggested never filling your tank above 1/2 and never letting it drop below 1/4. Funny how they didn't think about the fuel implications of stopping at least 3 times as often for gas.

I think that most of the tips were good. Sure, you can pick some apart, but if someone in the general public followed these suggestions, it would increase their fuel economy.

I am an auto broker and I see lots of bad driving habits in my clients. My job isn't to chastise them for doing so, but to make sure they understand how the car works and show them all the cool new features in their car. If they are driving their Prius like they drive their big American sedan, I warn them that they will not achieve the gas mileage on the window sticker. At least they can't blame the car, when their gas mileage isn't close to what they expected.

As I stated in another post, cars are made for specific purposes. A Prius is made for people who want high gas mileage and don't mind driving conservatively. Just as a Porsche Cayman S isn't made for a 90 year old woman, nor is a Ford F350 Dually with a lift kit.

'...Sure, you can pick some apart,...'

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Some?!? The problems I listed make up the majority of that web page. Did you look at the page?

The other two links are fine, even though some improvements could be made. I'm fine with web pages not being perfect.

I don't think it is good to recommend a web page when most of the info is questionable or wrong (all of it compounnded by poor writing).

I'm on the page right now and I don't think it's that bad. Some are iffy like the time of day. Some of the numbers may be off too, but if someone followed these tips, they would improve their fuel economy. The right type of oil - I agree. The author's choice of words on #3 are sketchy, but the idea is don't idle your car too long - I agree. Regular tune ups - good. Dirty air filter -good on that too. Tires to the right pressure - good advice. Snow tires are bad for mileage - okay on this. Remove excess weight - good advice. Smaller cars are typically more fuel efficient - yes. Manual transmission more efficient - not any more. Idling vs start stop - one minute isn't going to change much, so why put stress on your starting system? Keep it close to 55 mph - you'll get some angry drivers behind you, but it does save gas. Accelerate to the bottom of a hill - good advice. Rough road decrease gas mileage - true. Traveling the speed limit increases your chance of hitting greens - works a lot of the time. Use cruise control on the highway - I'll agree with that. Cool down auto trans by placing them in neutral - okay, this one can be a bad one for some cars - ZF trans in BMW's come to mind - don't idle them in neutral too long. Avoid reversing maneuvers - kinda silly, since it doesn't help much. Open sunroof reduces economy - this is true, I've tried it. Close windows on the highway and use A/C - true. Slow acceleration on the freeway - I think this is wrong, as I've been told to briskly accelerate to cruising speed.

I still think it's a good article for the layman. Just my thoughts!

You have no problem decoding and modifying the content to arrive at a couple pieces of good advice; you already know the things that improve mileage.

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Anyone who already knows the basics of driving more efficiently will be able to 're-combobulate' this atrocity and with a little re-arranging and reinterpretation, construct something that would have been worth putting on a webpage of that title.

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But making a webpage of advice that is only accessible by people who already understand the advice, rivals in stupidity some of the statements made on that actual webpage.

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An advice page like that doesn't have much positive function if you have to already know the advice to figure out what they should have said.

Maybe so, but I still think that many people could benefit greatly from this advice. Remember that most of us are in the field of science/engineering or were trained as such. We are definitely brighter than the average person, we are interested in things like this and most of us already know about the items in the first link.

I believe that the average driver doesn't know about these tips. I am by no means trying to demean the average person - I'm simply stating a fact about people. If they were interested in topics like this, they would've been scientists/engineers. It makes them no worse or better than us, just different.

As a test, show this list to some people you know who you consider laymen. People from church, neighbors, your secretary, receptionists, clerks at the grocery store, etc. I think you'll be shocked to find out that they will get a lot out of the article.

Again, I think it's great that we can have these discussions and we can share our own experiences. Thanks for the dialog!

I'm open to the idea. I'll show it to a few people and see what happens.

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I'll also try to limit my input to them as I already have an opinion about this piece.

Let us know what the outcome is. I'll do the same on my end and post my results.

Moving on to #3:

'.....When starting your car, you don't need to run it for more than 45 seconds. After that, you are just wasting fuel......'

This is moronic. If I only needed to run the engine for 45 seconds, I would have walked.

My understanding of what the author was saying here was not to run the engine for more than 45 seconds before driving off - ie. you dont need to warm it up before you hit the road.

Arriving at your 'understanding' requires significantly more than what was written.

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I agree that is likely what the author had in mind. I also think if that is what they had written, it would have been one of the more helpful things on the list.

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The thing is people who already know the things that improve mileage are probably going to be able to decipher the intended meaning easier, having previously seen the information.

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For that are not familiar with ways to improve efficiency, that webpage is unlikely to help much. The ineffectual writing doesn't help. Why trust someone to tell you how to effectively use your car, if among the very few things you know about that person is that they can't effectively run use their language?

Gotta agree with you. I think it clearly means that you should not idle your engine for more than 45 seconds. I don't think you need to be knowledgeable in fuel saving to understand this. I could be wrong, but it makes sense. It doesn't make sense to tell someone to run their car for less than 45 seconds, ie drive for 1-2 blocks and shut it off.

'.... It doesn't make sense to tell someone to run their car for less than 45 seconds, ie drive for 1-2 blocks and shut it off....'

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Exactly!

Does not the instrument cluster constantly display km/liter or miles/gallon?

Shouldn't be too difficult to find the speed/fuel-consumption sweet spot after a short time driving your routine.

At points less than wide open throttle your engines typically going to run most efficiently at or very near the RPM where its peak torque is at.

We know that engines are typically less efficient at partial throttle.

A good thing to know would be, roughly how much less efficient an engine would be at partial throttle and how that compares to running the engine at WOT but less than the most efficient RPM band.

Most BSFC maps I've seen are at WOT. It would be nice to have BSFC maps created at 1/2 throttle in order to compare.

Does anyone have good data on this they would be willing to share?

Something I have often wondered: I can drive at 50 mph in either 5th gear or 4th gear. Of course 4th gear is at a higher rpm, but with less load on the engine. Which will give more mpg? I very seldom drive at WOT.

If you're cruising at 50 mph in a modern car, you should have no trouble using 5th gear without overloading the engine. As you stated, using 4th will have a higher rpm in the engine, which means less efficiency due to more friction related losses. Also, it will be more wear on the engine. So even if there were a small savings in fuel, you would give it up in the increased maintenance and repairs.

The suggestion isn't about screaming down the road always at WOT. The suggestion is to know the BSFC map for your particular vehicle and realize that often, being closer to WOT in a higher gear will be more efficient in the long run.

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In most cars you can accelerate at a rate that is not excessive, near WOT, if you shift very early so that you are quickly in very tall gears.

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While fuel savings can be reaped with this approach with diesels, gasoline engines that have throttles often have even more to gain. The pumping losses incurred by low-moderate throttle position in an engine that truly has a throttle can be significant.

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Here is an interesting thread in ecomodder.com on the related subject of pulse and glide.

I give guidance to those who want to take the advanced driving test. One 26 year male had a Renault Clio Sport and after 4 drives he said that he thought the greatest difficulty with the advanced driving would be his journey to and from work (Renault F1). I suggested he drove for 1 week the way he normally drove before any guidance and 1 week the way I was encouraging him to drive. We met every 2 weeks. On his next session he showed me his results which were journey times of 22 minutes but the first week he averaged 30 mpg but the second week he averaged 38 mpg. His question to me was ' why should I drive like I used to?'

Anticipation, looking well ahead and using the engine (not gearbox) to slow down will increase the mpg. Most of my associates, with a range of cars, have an improvement of 10 % to 15 % on their mpg.

What does '...using the engine (not gearbox) to slow down...' mean?

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I definitely think anticipating to minimize having to brake/re-accelerate is definitely a very important skill needed to be a very efficient driver.

Sorry for the delay in responding.

When approaching junctions which are not mandatory stop junctions, Give Way (UK), stay in the same gear and use the engine to slow the vehicle, depressing the clutch (manual gearbox) to prevent stalling. Prepare to stop but look to go. If it is safe to proceed, make 1 gear change and go.

Most people change from say 5 to 4 then to 3 using the gears to help slow them down - useful for earlier types of vehicles with less effficient brakes. Another trait that a lot of drivers do is to depress the cluth, go through each gear position to their desired gear not releasing the clutch between each gear selection.

One other item to consider is the wind resistance and rolling resistance of the car. On every trip, your wind resistance will be different due to the density of the air, wind speed and wind direction. Since this is a variable, your graph of MPG vs speed will not work. Also, as your tires age, the rolling resistance will change. I've seen some that get better, while others get worse.

Looking at both of these variables, you're not going to be able to achieve the results you are looking for.

Some posted that the best way to gain efficiency is to alter your driving habits. I think that you'll gain the most mileage by anticipating stops/slowing down, cruising and accelerating. I believe that the most efficient way to drive modern cars is to accelerate briskly to your cruising speed and maintain that speed.

I would run weekly tests and do your best to optimize your gas mileage. But don't clog the motorways - that's a no-no.

Good luck and let us know how it works for you.

Gentlemen,

Sorry for the delay in getting back to this post. life has a habit of getting in the way of what you want to do!

Lots of information and food for thought. In relation to a few post.. Refueling at the coolest part of the day was something which was done by small fuel distributors from larger oil terminals. the tanks were over ground and were influenced considerably more than the underground tanks by changes in temperature. In modern fuel terminals/depots they have installed vapour recovery units to remove & condense fuel vapour and as such this is not really relevant anymore.

In relation to measurement using the instrument cluster, while it does provide average and current figures for MPG to compare it is very difficult. most of my driving is on Irish local roads so lots of turns, hills and getting caught behind buses, tractors etc. makes it hard to compare accurately as driving conditions are very variable.

In relation to the Resistances they are a huge variable and obviously influence the figures. i was looking for a best case/most optimal performance. I am not sure but i imagine the tests for manufacturers to advertise the MPG are not just calculations but also tests done in optimum conditions so as to get the highest value possible. While the optimal and real world conditions will vary i was hoping to try cruise at the best RPM and try increase the average MPG in that way..

Weight reduction and tyre pressure were options i knew and implement. the driving habits and anticipation are probably the harder ones to implement.

Thank you for the information guys