fuel consumption Automatic vs. Manual

[rverdoold]

In general its know that a automatic transmission uses more fuel than a manual. But looking at the specs of the Dutch subarus, shows otherwise.

The impreza and legacy using the 2.0R have a lower consumption with the automatic than with the manual gearbox. Only the 1.5R its otherway around. The 3.0 is a huge difference (up to 4 litres per 100 km) in advantage of the automatic.

 

So the excuse to take an manual is better for consumption is not true (of course it all depends on the way of driving as well.)

 

note: the numbers are for, city, outside and mixed

[Subarupusher]

I had the base manual Impreza 06 for a year and upgraded to an auto Impreza 07 4 months ago. I calculate my mileage every fill up. Here is what I have noticed.

 

The manual under optimum freeway conditions got me the mileage estimate on the sticker (29). The best I have gotten on the auto is 28 which also matches the sticker. Under mixed conditions the automatic does as well or better on mileage. The manual would get 24-25 and the automatic gets 25-26. I think there is more efficiency using an automatic in stop and go traffic which happens a lot in the Seattle area. I also noticed the automatic sticker city mileage estimate (23) is +1 compared to the manual sticker.

 

So it is a matter of your driving environment. Long open highway drives favor the manual and urban driving favors the auto. The auto is also easier on my middle aged knees when you have a lot of clutch play in stop and go traffic.

[nipper]

In general its know that a automatic transmission uses more fuel than a manual. But looking at the specs of the Dutch subarus, shows otherwise.

The impreza and legacy using the 2.0R have a lower consumption with the automatic than with the manual gearbox. Only the 1.5R its otherway around. The 3.0 is a huge difference (up to 4 litres per 100 km) in advantage of the automatic.

 

So the excuse to take an manual is better for consumption is not true (of course it all depends on the way of driving as well.)

 

note: the numbers are for, city, outside and mixed

 

Well its almost a tie. the throw in the cost of or a clutch if you keep the car long enough, that auto wins. Computer controled automatics are almost as effecient as the manuals, so now its just personal taste.

 

nipper

[mnwolftrack]

I would agree, that as automatic transmissions get more and more sophisiticated, the mpg discrepency between auto vs. manual is decreasing and in some cases reversing roles. I've seen a few EPA ratings lately that showed manual vs. automatics tied, and a few of them were even showing the auto getting 1 or 2 mpg better than the manual.

 

My heart still belongs to manual transmissions though. Way more fun to drive and safer to drive in slippery conditions. Downshifting in 4WD or AWD is much better than braking. While you can technically downshift an automatic, you cannot control how long it takes for the torque converter to fully lock. With a manual transmission, you can milk the pedal and create slow grab time during incliment weather to minimize slippage.

[idosubaru]

the auto's weigh considerably more, that's one difference that isn't going away. don't forget to look up the track times of the auto's vs. manuals as well - you'll see some auto's recorded with slightly better or equal times.

 

also the gear ratios are different, i think this matters as well. a manual AWD XT6 and a 4EAT AWD XT6 can both get nearly the same highway gas mileage. the auto at highway speeds will run 3,000 rpms while the manual runs nearly 4,000 at the same speed. i do not know if that makes a difference, but it sure seems like turning your engine over 750-1000 times more per minute would take more energy. in this case i think the less efficient auto is counteracted by a more highway friendly gear ratio.

[nipper]

the auto's weigh considerably more, that's one difference that isn't going away. don't forget to look up the track times of the auto's vs. manuals as well - you'll see some auto's recorded with slightly better or equal times.

 

also the gear ratios are different, i think this matters as well. a manual AWD XT6 and a 4EAT AWD XT6 can both get nearly the same highway gas mileage. the auto at highway speeds will run 3,000 rpms while the manual runs nearly 4,000 at the same speed. i do not know if that makes a difference, but it sure seems like turning your engine over 750-1000 times more per minute would take more energy. in this case i think the less efficient auto is counteracted by a more highway friendly gear ratio.

 

Except your using a 20 year old car to use as a comparison.

 

We are talking new cars here, 2007 model i do beleive, so your comparing apples and oranges.

 

Weight really is a moot issue, as automatics are no as near as heavy as they used to be (they are getting pretty close to being equal weight)

Also your assumption is wrong about gear ratios. You have a thing called a torque converter, which actualy multiplies torque, thats why you can run higher gear ratios. And its not the cruise speed that it helps or is imporatant, its the starting off the line. The torque converter multiples torque, so you can have taller gears, where as a manual does not, so the gears can not be as tall for the benfit of acceleration.

 

Like all things in engineering, everything is a compromise.

 

 

nipper

 

Correction 15 year old car

[idosubaru]

Except your using a 20 year old car to use as a comparison.

showing that this is not a new concept and has been around awhile. if it is apples to oranges then the reasons the XT6 trans get the same gas mileage is.....different than why the new ones do?

 

an engine running at 1,000rpm will get different efficiency when running at 7,000. assuming that curve is continuous (which it is) logic suggests that 1,000 rpm's can make a difference, but i see your point that maybe it is negligible.

[nipper]

showing that this is not a new concept and has been around awhile. if it is apples to oranges then the reasons the XT6 trans get the same gas mileage is.....different than why the new ones do?

 

an engine running at 1,000rpm will get different efficiency when running at 7,000. assuming that curve is continuous (which it is) logic suggests that 1,000 rpm's can make a difference, but i see your point that maybe it is negligible.

 

AHA!

 

hehehehe

 

 

nipper

[rverdoold]

Not to sure about manuals being better on the highway long runs. I noticed during my holiday in the baltic region of Europ i drove long distances at 90 km/h at this speed the lock-clutch is locked and consumption is like a manual only the final gear ratio is slightly worse. With my '91 legacy i even managed to drive 415 km on 33 litres only (dunno the quick convertion to mpg but ~30.5 mpg) ok this was only once of the 4500 km holiday. But average was ~28 mpg (98 octane) over this distance of which 2500 on very bad dirt roads.

I think 28 mpg is very good for an old car especially an automatic.

[hankosolder2]

showing that this is not a new concept and has been around awhile. if it is apples to oranges then the reasons the XT6 trans get the same gas mileage is.....different than why the new ones do?

 

an engine running at 1,000rpm will get different efficiency when running at 7,000. assuming that curve is continuous (which it is) logic suggests that 1,000 rpm's can make a difference, but i see your point that maybe it is negligible.

 

Does Subaru offer 6spd manuals on normally aspirated cars? That seems like the way forward...

 

I see Nipper's point about how torque converters will allow 'auto' cars to run taller gears, however, I suspect that Subaru also designs their manual trans gear ratios so that minimal downshifting is needed on the highway. For example, my '99 Honda Accord is doing just about 80mph at 3K rpm in 5th. '98 Outback runs at over 4k rpm at the same speed in 5th and is really irritatingly buzzy. The irony of this is that the Honda is an engine with a much higher RPM torque peak than the Subaru.

 

Nathan

[nipper]

Does Subaru offer 6spd manuals on normally aspirated cars? That seems like the way forward...

 

I see Nipper's point about how torque converters will allow 'auto' cars to run taller gears, however, I suspect that Subaru also designs their manual trans gear ratios so that minimal downshifting is needed on the highway. For example, my '99 Honda Accord is doing just about 80mph at 3K rpm in 5th. '98 Outback runs at over 4k rpm at the same speed in 5th and is really irritatingly buzzy. The irony of this is that the Honda is an engine with a much higher RPM torque peak than the Subaru.

 

Nathan

 

Yes you have to look at the power band of the engines. Alot of v-8 engines with automatics are just off idle at highway speeds (below 2000 rpm) on flat ground. They rely on the torque converter and puter to react when the little pedal is pushed.

 

Also the aerodynamics etc etc etc. Look and see where the power band is for the accord, the subaru is about 3200 rpm (i think). IN a manual you want to keep the car just shy or on the bottom edge of the power band so you dont have to downshift.

 

This is why your seeing 6, and soon to see 8 speed automatics. The idea is to keep the engine right in the peak of the power band, so that fuel isnt wasted off the powerband peak. This way the fuel is being used most effeciently.

 

nipper

[idosubaru]

'98 Outback runs at over 4k rpm at the same speed in 5th and is really irritatingly buzzy.

the high noise at highway speed annoys me too. i'm not that picky, but that's one thing i'm not fond of.

[nipper]

the high noise at highway speed annoys me too. i'm not that picky, but that's one thing i'm not fond of.

 

me too

 

nipper

[cookie]

It's going to be a long time but they are both on thier way out. The main way automakers are adressing mileage and polloution is the powertrain.

[bulwnkl]

This is why your seeing 6, and soon to see 8 speed automatics. The idea is to keep the engine right in the peak of the power band, so that fuel isnt wasted off the powerband peak.

I disagree. 6 and 8-speed automatics are primarily marketing motivated. The torque convertor essentially eliminates the need for such foolishness, and a CVT is better at keeping the engine at torque peak and is MUCH lighter weight.

 

The reason automatic transmission vehicles have equal or better highway ratings (when they do) is entirely from gearing. On the highway, the torque convertor clutch is locked so the only difference between an A/T and an M/T in terms of mpg is engine rpm. In city driving, it is my belief that Subaru's recommended shift points in their M/Ts combined with engine output characteristics are such that the A/Ts keep rpms lower, again raising mpg. If it was not for that, the A/T wouldn't have a prayer because of the energy loss through the fluid coupling.

[hankosolder2]

Is it possible that the different AWD mechanisms (AT vs MT) might come into play with the mileage discrepancy? I doubt it, but it seems POSSIBLE that the stong FWD bias in the AT cars might result in less drivetrain losses?

 

I agree that the trend towards ridiculous numbers of gears in automatics is silly. Five well chosen ratios are plenty for a country which does not have an Autobahn! Variable valve timing increases the width of the torque peak on modern engines- hence fewer gear ratios should be sufficient!

 

Nathan

[mnwolftrack]

There's at least one car out there with an automatic transmission that has no gears. I forget which car, but I'd like to say it was a Nissan or Honda. I recall seeing advertising for it at least a year ago. The TV ad touted how there was no shifting of gears, no jerky shifts, etc.... I have no idea what technology was used, but perhaps the upcoming trend is to just design things that are different, e.g. not a 4 or 5 speed automatic. Besides, the U.S. seems to think more = better, so there may also be a touch of marketing being done.

[ron917]

What you are describing is a Continuously Variable Transmission (CVT). Instead of gears, it has a metal belt and variable pulleys. Many manufacturers are using them now - Nissan, Ford/Volvo, Chrysler are the ones that I know of that are available currently in the US. They've been tried in the past, but with poor reliablity. The old Subaru Justy had a CVT.

 

Do a google search, there's lots of info out there.

[bulwnkl]

Is it possible that the different AWD mechanisms (AT vs MT) might come into play with the mileage discrepancy? I doubt it, but it seems POSSIBLE that the stong FWD bias in the AT cars might result in less drivetrain losses?

 

You know, I've often wondered about that. It seems to me that it could not be a factor because:

 

There is no way to disconnect the rear hubs or driveshaft. That means that you're turning all that mass all the time no matter what. When the center clutch mechanism engages, you're driving it from the transmission through to the road, and when it disengages, you're driving it from the road through to the transmission. So, it seems like it should be the same energy needed and therefore the same mpg either way?

[rverdoold]

What you are describing is a Continuously Variable Transmission (CVT). Instead of gears, it has a metal belt and variable pulleys. Many manufacturers are using them now - Nissan, Ford/Volvo, Chrysler are the ones that I know of that are available currently in the US. They've been tried in the past, but with poor reliablity. The old Subaru Justy had a CVT.

 

As Dutchman i should be very proud on the CVT which was invented by DAF trucks here in holland. The idea was to make a new transmission which could handle all the load and would use the egines maximum torque at the right moment.

Ferrari tested the CVT for use in the F1 cars but after 1 race the idea got disqualified by the FIA. Actually the quality of gearboxes are developed in automotorsport. Imagine DSG (direct sequential gearbox) was never inveted for a VW lupo/polo/golf (small ones).

Subaru still thinks CVT is good, me too, i have driven it and its really nice. Very strange because at the momement you floor the pedal it goes imediately to 5500 to 6000 rmp but speed is later. There is no feeling between rpm's and car speed anymore.

Subaru is busy developing a CVT for use in the legacy ect. i can only imagine that it will be in combination with a hybrid egine (like all hybrids from toyota have). Als well a e-CVT has preprogrammed positions, called 'gears' but this would not be necessary its made to give people a more 'gearbox control' feeling.

The nice thing of CVT is that you can drive as fast as forward as in reverse .

 

And yes i have the autobahn at 15 minutes away from my houses and nothing is nicer to floor the pedal on the onramp and let it go at 200 km/h:grin: (or topspeed). Just sometimes fuel consumption is not an issue. OMG that boxer sound is so nice. (untill now done with, 91 legacy 2.0, 05 OBW 2.5, 06 legacy B6 3.0) (ah the WRX STI impreza is still on the wishlist:) )

[nipper]

I disagree. 6 and 8-speed automatics are primarily marketing motivated. The torque convertor essentially eliminates the need for such foolishness, and a CVT is better at keeping the engine at torque peak and is MUCH lighter weight.

 

.

 

I meant 6 speed, 8 speed is under development.

 

You can disagree, but thats the technical reason for it. They are not going to spend literally 720 million dollars on a marketing gimick. Also this transmission was designed as a joint venture, between Chrysler, Ford and GM (chrysler was part of the original deal, and seems to have parted ways with thier sale)

http://car-reviews.automobile.com/news/gm-and-ford-develop-6-speed-automatic-gearbox-in-cooperation/263/

 

The interesting thing is that they made it so that it can be front or rear wheel drive. That makes for a very compact transmission. Each mfg will have the TCU tuned to thier own brand "personality"

 

With a 4-8% increase in fuel economy fleet wide. CVT's are a gimmick that are not going to take off. There have been buyer complaints of the drone of the engine and lack of shift points. Customers just dont like them.

 

http://www.autoblog.com/2005/11/09/breaking-news-fords-new-six-speed-automatic/

 

"Short steps between intermediate gears enhance performance and feel by finding the right gear for the most efficient operating conditions. The smooth shifts reduce harshness and reduce overall NVH."

 

 

 

Also Dont forget, I am in the engineering end of the automotive field. I get the inside scoop on things

 

nipper

[bulwnkl]

I don't doubt your engineering, Nipper, though I may assert (I don't right now, but I may ) that your ties to engineering cause you to underestimate marketing. Frankly, 720 million dollars on marketing is cheap money well spent if it gets you the customers.

 

The simple fact of the matter is that a CVT is technically superior to a conventional A/T for all the reasons cited in this thread. If customers don't like them that's a marketing issue (gimmick may not be the optimum term for this specific issue), not a technical one. In point of fact, marketing drives engineering as I'm sure you know.

 

The 2-speed A/Ts common in the '50s and '60s were excellent units (well, I only have experience with the GM units and they were excellent). Similarly, the 3-speed automatics common on small cars until fairly recently were also excellent and, just like 14" wheels (and even 13") in those applications, were demonstrated by their manufacturers to be superior technically to the 4-speeds (and 15 and 16" wheels) which replaced them. They were replaced almost entirely because of marketing factors. Just as sales have demonstrated time and time again that bigger=better (in terms of sales), they have also demonstrated that more=better (in terms of sales). 6- and 8-speed A/Ts are no different.

 

So as you said, you can disagree, but that's the (marketing) reason for it.

[hankosolder2]

I meant 6 speed, 8 speed is under development.

 

You can disagree, but thats the technical reason for it. They are not going to spend literally 720 million dollars on a marketing gimick.

With a 4-8% increase in fuel economy fleet wide. CVT's are a gimmick that are not going to take off. There have been buyer complaints of the drone of the engine and lack of shift points. Customers just dont like them.

 

"Short steps between intermediate gears enhance performance and feel by finding the right gear for the most efficient operating conditions. The smooth shifts reduce harshness and reduce overall NVH."

 

nipper

 

Nipper,

You never addressed my point, namely that with variable valve timing, tuned intakes, etc, today's engines have much wider torque bands than ever before, and should be able to have good performance and economy with the same or fewer gear ratios! The 'sweet spot' is wider than ever.

Can you imagine having to pay for a transmission overhaul on one of these six speeders? I can't wait 'till the local AAMCO takes a crack at that!

Car makers spend millions restyling cars, sometime with no functional or even cosmetic improvement- that should be proof that the lure of a marketing 'gimmick' is sufficient motivation to make carmakers willing to spend millions.

BTW, computer controlled CVT transmissions can be programmed to have discrete shift points. The MG MGF was sold in England with a computer controlle dCVT option- you could have 'seamless' CVT shifting or something like eight 'ratios' (steps) which could be manually or automatically shifted between depending on dash switches & paddles. I'm not totally sold on CVTs, but it's a possible option.

 

Nathan

[destey]

But looking at the specs of the Dutch subarus, shows otherwise.

The impreza and legacy using the 2.0R have a lower consumption with the automatic than with the manual gearbox.

 

Could be due to imperfect gearing. Or another factor I can't think of. I've achieved as much as 31.5 mpg on my '95 legacy (2.2L), 5spd. Usually I get 29-30.

 

My parents have the same car in a automatic, and that gets 25-28 mpg.

[nipper]

Dutch subarus also arent rated by the US epa, they are done by the european agency (or dutch) which i am very sure have an entirely different method of testing gas mileage.

 

 

nipper