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Old 28th September 2011, 21:57   #1
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Default The curious case of highly varying FE during city & highway driving

I drive a Opel Corsa 1.4 Sail and I absolutely adore the car. Apart from the fact that it is out of production and expensive to maintain, there's only one thing that doesn't favour the Corsa : Fuel Efficiency.

On a typical Indian street with moderate to bumper-to-bumper traffic, my Corsa returns an average FE of 11 kmpl; and this is when she and I both are on our best behaviour. Mind you, the car is very well maintained.

Switch the a/c on and I actually see the needle moving towards E on a 10km drive!

Now, I've taken the Corsa on 3 long drives - all on beautiful highways. I generally keep the a/c on at blower speed 1 and maintain ~90 km/hr. With ~3 people on board and average luggage, the car returns an astonishing FE of 16 kmpl; during a 100 km stretch of steady driving, even 18 kmpl!

Eg. On my drive to Manipal, I drove through NH4 and then NH48. Except for the Shiradi ghat stretch where the 30km stretch took my 1.5 hours, the rest of the 450kms journey had amazing roads. Excluding the 30kms, I had around 18kmpl and including it, 15 kmpl. I observed a similar thing during the Hampi drive.

Now, that's got me thinking. Agree, highway driving without doubt makes the engine run at its optimal best. But a difference of 8 kmpl?! That is huge.

Are/can engines be tuned in such a way that they perform exceedingly well when continually driven at optimal driving conditions?

The recent Nissan Sunny review has mobike and Rehaan mentioning how the 1.5l engine lacks punch - clearly a sign that the engine has been tuned for better FE. Engine tunings are also carried out for the converse (high BHP and less FE)

Is there something in the engine that is tuned in a way that makes it brilliantly fuel efficient in a condition and terrible in another? Especially Opel cars?

Compromise power for FE, make the engine peppy.. What else do manufacturers do to engines to make the cars sell?

MODS : If you feel this should be in my ownership thread for Corsa, please merge.
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Old 28th September 2011, 22:44   #2
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Default Re: The curious case of highly varying FE during city & highway driving

What a coincidence! was rummaging through the threads for exactly the same Question. I have a indica v2 diesel, on my day to day city crawling (i cover 7 km in an hour) i get an FE of 10.5 - 11 kmpl. When i too drove down to hampi this april the vehicle returned a very decent 19.5 - 20 kmpl. More recently when i drove down to mahableshwar i got FE of 17 when going and 19.5 when returning.

Have seen similar behaviour from my fiesta petrol 1.4. The city figures were a dismal 7.5 last time, was wondering if things had gone wrong. Took it to pune this monday covered 360+ km and the needle is just a little below the halfway mark, havent tanked up yet but i guess it would have returned around 16 kmpl.

With the fuel prices headed north i sure would like to know how to extract a little more juice when driving in the city. I read elsewhere that keeping the A/C on while idling consumes a lot more fuel than just idling without the A/C. Any ideas what this percentage could possibly be.

Thanks!

Last edited by cyberwhizs : 28th September 2011 at 22:50.
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Old 29th September 2011, 05:36   #3
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Default Re: The curious case of highly varying FE during city & highway driving

Well traffic driving does bring down the average to a large extent, what i have observed is in smaller cars the difference is large (City/Highway fuel efficiency) in larger cars the difference is less. I remember my Indica petrol going from 12 to 18+ between city and highway. My Baleno gives 11/16 between city/highway. I believe today's 1.8's in the market are more closer when driven in City or highway something like 10/14 on a Altis.

The new cars with MID and all tell you instant fuel efficiency and it does help in figuring out what kind of driving isnt a good driving from fuel consumption point of view. One could see the eff figures going up and down as you deal with bumper to bumper traffic.
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Old 29th September 2011, 10:49   #4
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Default Re: The curious case of highly varying FE during city & highway driving

The worst FE my Alto K10 has given is 10.5. That is with AC in a B2B traffic, where a 10km stretch takes one hour. The major reason is that at each traffic signal the car is not moving, but the AC is consuming power. In a similar situation without AC the car would give an FE of 13-14. Now on highway, I have got 19+ with AC. The reasons are :
. There is no time wasted at traffic signals. So most of the petrol consumed goes for locomotion and not cooling the car when stationary.
. Highway travel is predominantly done in the fifth gear, hence higher FE. B2B in contrast is mostly in 2nd and 3rd, with 4th coming in short bursts.

As pointed out, the bigger the engine, the less is the difference, because the AC consumes less portion of the power and the fuel consumed at idling is proportionately much less compared to fuel used for locomotion. I have noticed this in my neigbour's Altis, he gets 8-10km/l in B2B, and 12-14 on highways.
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Old 29th September 2011, 11:08   #5
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Default Re: The curious case of highly varying FE during city & highway driving

My Sonata Embera AT gives me 5.5 - 6.0 in city driving (office commute) and 11.0 - 11.5 on the highway.

Difference:

City runs are short, less than 10km runs, mostly in traffic where the car never even gets into fourth. (It's an automatic and only slots into fourth around 60kmph. I've tried using the tiptronic-style shifter to coax it into fourth but it won't obey.) With constant stop-and-go, having to move a big heavy car is no fun for the engine.

Once on the highway and at speed, all the engine needs to do is produce enough power to push the air out of the way. Steady, high-speed driving yields phenomenally better mileage, literally double in my case.
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Old 29th September 2011, 11:39   #6
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Default Re: The curious case of highly varying FE during city & highway driving

If I were to answer technically, in a very basic way:

1. For an equal number of revvs, the average kilometers covered during the city and highway, are very different. While on the highway, you cover much more kms.

2. City Drives means; frequent gear changing, or.. the engine has to respond to much frequent changes in load requirements, or throttle input. Now, for the FE part of the engine, this is very unfriendly. You simply waste fuel, which otherwise could have been burnt, had the engine been revving the same way.

3. Every engine has its sweet spot. ie, an optimum revv band, where there is optimum power and torque and the engine is most efficient in propelling the car. (Also considering the gear ratios). Now while on a highway, sometimes, you hit that spot, and go miles. Whist city stunts, the load requirements means that you never hit that spot and continue.

4. While on the highway, the engine runs much cooler.


Well, libran, in your case, whats happening is: The Corsa is a heavy car, and accelerating the car requires more fuel. Hence, city runs cost you FE. Also, the gearing in your car 'might' be highway friendly.

That said: Yes, it is very much possible to get the figures you mentioned. Try ripping the car in the city, and the gap widens.
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Old 29th September 2011, 12:06   #7
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Default Re: The curious case of highly varying FE during city & highway driving

These days the Zen gives me 12-13 kpl with AC in city ( always below 2000rpm/60kph in 50th gear) and about 16-17 with AC on the highway with speeds usually around 80-100kph .

But I have noticed that tire pressure does play a very big factor in FE and the Zen is engine is very sensitive to this .


The Lancer with 1.2L kms ,gives close to 10 kpl in the city and around 14 on the highway with AC on 100% of the times.I admire the lancer for being such a superb car ,as my brother hardly services it till the car breaks down and still it goes on and on and on .

The ANHC gives around 11 in city ( but city driving in Mangalore is like a highway ,but with heavy traffic which means frequent gear changes ) and around 17 on the highway with speeds around 100 kph with AC
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Old 29th September 2011, 13:06   #8
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Default Re: The curious case of highly varying FE during city & highway driving

Note from Mod : Please do NOT take the thread off-topic for your own benefit.

Last edited by GTO : 30th September 2011 at 16:30. Reason: Please do NOT take the thread off-topic for your own benefit.
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Old 30th September 2011, 13:06   #9
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Default Re: The curious case of highly varying FE during city & highway driving

I have had similar experience in our old M800. It gives 13-14Kmpl(city with 50% ac) and 21+ in highways with steady speed between 70-90.

Though i am not a technical person,i would like to say that the frequent gear changes coupled with the constant acceleration and deacceleration are responsible for the low FE in the city. The engine doesn't get to settle down and is constantly worked up.

Also as mentioned above,at junctions,the car is running(with/without AC) and is sipping petrol but with no distance covered. Imagine the KMS you could have covered at 80kmph on a highway in the same time you spent at the junction(though the engine RPM was slightly lower during the wait).

I would like to give a rudimentary example. Imagine you are riding a bicycle. You rode in city as well as in highway. You will agree that it is more difficult to ride in the city,
pedal hard and gain speed ->slow down in the next moment ->again pedal hard to gain speed....it just goes on.

On the highway- pedal hard to gain speed -> relax after a speed is achieved -> a little 'light' pedalling is enough to maintain a speed(provided road is smooth).

I hope you got something from my silly example
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Old 30th September 2011, 15:06   #10
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Default Re: The curious case of highly varying FE during city & highway driving

Quote:
Originally Posted by dhanushs View Post
Also, the gearing in your car 'might' be highway friendly.
Precisely the point of discussion in this thread.

What would have been the line of thought for such a thing? Esp. in India. Or the Germans simply imported every bit of the car and started selling in India without configuring it for Indian conditions.

Quote:
Try ripping the car in the city, and the gap widens.
Oh man, I don't have the heart for that. 10 kmpl and 75 rs/l; every drop counts!
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Old 30th September 2011, 17:02   #11
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Default Re: The curious case of highly varying FE during city & highway driving

Quote:
Originally Posted by dhanushs View Post
Also, the gearing in your car 'might' be highway friendly.
I am not so technically inclined, so I am not aware if HIGHWAY friendly gearing is a possibility. It might be, going by the technological advances, but my point is if you can distinguish HIGHWAY and CITY gearing for a car, then wouldn't all small hatchbacks aimed at city running would come with city favoured gearing to extract the most out of the fuel?
IMO, this behavior of low FE in city and high FE on highway is observed in all segments of the car irrespective of their engine sizes and gearing.
My Ikon exhibits the same traits, city mileage of around 10-11kmpl and highway mileage of 17kmpl.

Quote:
Originally Posted by ashis89 View Post
Also as mentioned above,at junctions,the car is running(with/without AC) and is sipping petrol but with no distance covered. Imagine the KMS you could have covered at 80kmph on a highway in the same time you spent at the junction(though the engine RPM was slightly lower during the wait).
Quote:
Originally Posted by dhanushs View Post
2. City Drives means; frequent gear changing, or.. the engine has to respond to much frequent changes in load requirements, or throttle input. Now, for the FE part of the engine, this is very unfriendly. You simply waste fuel, which otherwise could have been burnt, had the engine been revving the same way.
These reasons quoted above IMO best explains why city mileage is low.
A-B-C then change gear and again the same process frequently takes toll of FE during city driving.
While on highway you can maintain a constant speed for longer time, which requires less clutch usage and lesser braking instances which increases the FE.
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Old 30th September 2011, 17:16   #12
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Default Re: The curious case of highly varying FE during city & highway driving

In my case,not much of a difference.
Indica xeta- City 12-14(depending on the traffic and load)
Highway 16-17 (speeds around 90-110)
Palio S10- City 8-10
Highway 12-14(100-120)

Wish i could extract more mileage in highways :-(
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Old 30th September 2011, 17:31   #13
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Default Re: The curious case of highly varying FE during city & highway driving

Of course if you drive fast on highways, your FE will go down. My son's Baleno gave 17+ with AC on highway when driven at 80-90, but dropped to 12- at 150+. In city it gave between 7 and 9 with AC.
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Old 30th September 2011, 23:13   #14
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Default Re: The curious case of highly varying FE during city & highway driving

Quote:
Originally Posted by libranof1987 View Post
What would have been the line of thought for such a thing? Esp. in India. Or the Germans simply imported every bit of the car and started selling in India without configuring it for Indian conditions.
Actually, most cars selling in India, especially hatch backs have tall 5th gear. And, that's also one of the reasons that, in some cars you reach the top speed in 4th and not 5th.

This is particularly intended for good FE during highway drives.

Well, if companies made the shorter gears (1-2-3) taller, then it would affect the driveabiltiy, and in some cases also result in poorer FE. So, just hope that you got the best out of the many combinations. . One case, of bad 1-2 gear ratios is the Punto 1.3mjd, and may be the Polo 1.2 Tdi. The Swift on the other hand, is beautifully geared.

Quote:
Originally Posted by libranof1987 View Post
Oh man, I don't have the heart for that. 10 kmpl and 75 rs/l; every drop counts!
Well, once in a while you gotta let it go. After all, 'A man's gotta do, what a man's gotta do', eh?

Last edited by dhanushs : 30th September 2011 at 23:15.
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Old 30th September 2011, 23:20   #15
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Default Re: The curious case of highly varying FE during city & highway driving

Quote:
Originally Posted by dhanushs View Post
2. City Drives means; frequent gear changing, or.. the engine has to respond to much frequent changes in load requirements, or throttle input. Now, for the FE part of the engine, this is very unfriendly. You simply waste fuel, which otherwise could have been burnt, had the engine been revving the same way.
The Ikon manual has a nice graph which depicts FE in different gears. Unfortunately I dont have the manual (and the car) now. Is it possible to post the graph here?
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