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Old 25th March 2010, 11:10   #1
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Default Fuel efficiency assessment as a criterion in new cars

Here is one for the experts - in two modern and new cars, having similar engines - say a 1.2 petrol - can there really be a big variation in the FE between two makes? I ask this because the advertised FE numbers, even the ARAI certified ones, seem to have no bearing on reality in terms of maintaining the difference between the numbers for any two makes in real world conditions. Or so I think.There is so much that goes into the realized FE from driving conditions, to tyre pressures, to even measurement of the FE that I am not sure that buying a car because its stated FE is better than another is the right thing to do.
What I am trying to get at is that if I am looking at two cars, and once both have the same engine capacity and same fuel driven engine, can I assume that there will, at the end of the day, and in real life, be no significant difference in the actually returned FE. Assuming that both are new cars at roughly the same price points/segments. How I maintain the car and how I drive it would have a far greater impact on the returned FE?
I ask this because no maker seems to have anything radically different in engine tech that should allow for anything significantly different in terms of how fuel efficient the engine will be. Would that be a fair assumption to make?
If anyone disagrees, examples would be good to have as a basis for that.
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Old 25th March 2010, 13:30   #2
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Putting my 2 cents forward:
When I was picking up my recent car that was the concern I had as the mileage projected was different to what I was driving earlier. To the best of my knowledge, ARAI has a standard test where they put all cars through the same loading, speed, fuel quality, etc etc. The difference in mileage is acquired as an average of certain number similar test iterations.

Coming to the point, in real life things that affect the mileage of your car:

1. Your travel route and time (amount of traffic)
2. Your driving style (sedate or aggressive)
3. Load in the car (1-5 passengers)
4. AC usage
5. Quality and quantity of fuel (fuel stations do short change you)
6. Gearing ratios of your car (short ratio vs. long)

If you consider all these and I am sure I missing a lot more you will be able to ascertain the realist attainable FE. (I don’t even try )
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Old 25th March 2010, 13:46   #3
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Quote:
Originally Posted by Mafia View Post
Putting my 2 cents forward:
1. Your travel route and time (amount of traffic)
2. Your driving style (sedate or aggressive)
3. Load in the car (1-5 passengers)
4. AC usage
5. Quality and quantity of fuel (fuel stations do short change you)
6. Gearing ratios of your car (short ratio vs. long)

7. kerb weight of your car
8. engine design - i.e. bore/stroke/weight/vintage
9. Fuel type
10. Induction using turbo charging or super charging
11. ECU map (for lean or rich burning at engine speeds etc)
12. Tyre pressure
13. Rolling resistance of tyres (tread, profile, width of tyres)
14. Aerodynamics
15. Start / stop atitude at signals
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Old 25th March 2010, 13:55   #4
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Quote:
Originally Posted by Sawyer View Post
no maker seems to have anything radically different in engine tech that should allow for anything significantly different in terms of how fuel efficient the engine will be. Would that be a fair assumption to make
You are right about this. A good example would be the MJD engine from Fiat that does duty in a host of cars. A few car manufacturers who use this engine have tuned it for economy, some have tuned it for power - this in a way explains why the same MJD mill puts out different power ratings in different cars. All things being the same with the engine, it will come down to external influences such as driving style (IMO, the biggest factor), load, etc that will ultimately determine the FE of the car the engine is being used in.
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Old 25th March 2010, 14:48   #5
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So is there any example that any one can think of, of two engines of different makes, but using the same fuel, and the same cc that are giving FE returns that vary more than measurement and driving style caused differences?
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Old 25th March 2010, 14:52   #6
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ARAI should use more real life drive test and publish the numbers rather than some ideal tests. I remember seeing that Civic AT is claimed to have some 13 kmpl FE according to them! It is at least 2 kmpl less in real life...

Last edited by vasoo : 25th March 2010 at 14:53.
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Old 25th March 2010, 15:15   #7
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Originally Posted by Sawyer View Post
So is there any example that any one can think of, of two engines of different makes, but using the same fuel, and the same cc that are giving FE returns that vary more than measurement and driving style caused differences?
The Hyundai I10 1.2 Kappa and the Suzuki 1.2 K-Series engine.
I don't know what they put in those two, but H gives lesser mileage than S. You will see a thread dedicated to FE woes of 1.2 Kappa only.
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Old 25th March 2010, 15:29   #8
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Originally Posted by amitoj View Post
The Hyundai I10 1.2 Kappa and the Suzuki 1.2 K-Series engine.
I don't know what they put in those two, but H gives lesser mileage than S. You will see a thread dedicated to FE woes of 1.2 Kappa only.
I will look that up - actually I am surprised to hear that, I have an i 20 with the same engine in it, and the only time I keep tabs on the FE is on highway runs, when I have consistently got 17/18 kms a litre. I would think that the i 10 would at least equal that, is the Suzuki very much better?
Anyone who knows the ARAI measured numbers for the two engines, please post them.
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Old 25th March 2010, 15:41   #9
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Quote:
Originally Posted by Sawyer View Post
I will look that up - actually I am surprised to hear that, I have an i 20 with the same engine in it, and the only time I keep tabs on the FE is on highway runs, when I have consistently got 17/18 kms a litre. I would think that the i 10 would at least equal that, is the Suzuki very much better?
Anyone who knows the ARAI measured numbers for the two engines, please post them.
I don't have the ARAI figures for Hyundai, but I'm posting the fgures for the K series gems from Suzuki.

Ritz K12M - 17.7 kmpl
Swift K12M - 17.9 kmpl

EDIT : You get 17-18 kmpl on an i20 petrol? That's the highest I have heard so far.

Last edited by longhorn : 25th March 2010 at 15:52.
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Old 25th March 2010, 15:44   #10
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Quote:
Originally Posted by vasoo View Post
ARAI should use more real life drive test and publish the numbers rather than some ideal tests. I remember seeing that Civic AT is claimed to have some 13 kmpl FE according to them! It is at least 2 kmpl less in real life...

vasoo , your signature reads HONDA CIVID...
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Old 25th March 2010, 15:48   #11
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I think you need to add the transmission loss, suspension to the factors that affect FE also. It could be too simplistic to say engine technologies are same everywhere.
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Old 25th March 2010, 15:56   #12
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One of the most significant factor is how well built the car is.

Kerb weight of the car varies significantly among different cars having same engine capacities and similar power ratings.

While added weight *may* give better stability and ride, it takes toll on the FE. Of course, other parameters such as low-mid range torque will come into picture later.

Last edited by RX135 : 25th March 2010 at 15:57.
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Old 25th March 2010, 16:01   #13
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Originally Posted by RX135 View Post
Kerb weight of the car varies significantly among different cars having same engine capacities and similar power ratings.

While added weight *may* give better stability and ride, it takes toll on the FE. Of course, other parameters such as low-mid range torque will come into picture later.
+1 to that. Which is why the lighter Swift with the exact same engine as the Ritz gives 0.2 kmpl more.
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Old 25th March 2010, 16:13   #14
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Quote:
Originally Posted by longhorn View Post
I don't have the ARAI figures for Hyundai, but I'm posting the fgures for the K series gems from Suzuki.

Ritz K12M - 17.7 kmpl
Swift K12M - 17.9 kmpl

EDIT : You get 17-18 kmpl on an i20 petrol? That's the highest I have heard so far.
As I wrote, that is on the highway - to and fro to Mumbai on the e way a few times. The e way alone, it may well hit 20, but that is an exceptional road to cruise on.
Does anyone have the ARAI numbers for Hyundai?
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Old 25th March 2010, 16:14   #15
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ARAI figures are on a test-track and only reflect an ideal scenario with no stops and the testing constantly done at an optimum speed in the tallest gear.

Even if similar engine sizes are being compared in the real world, there is no generalization that can be done to arrive at a pre-determined conclusion about their mileage figures. Fuel quality, car weight, aerodynamics, gearing and resultant individual driving styles ensure that mileage figures will always vary between them.
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