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Old 18th February 2008, 15:59   #31
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The best theoritical FE is at the RPM in which the max torque arrives..

Personally any speed < 120 makes one go to sleep. @ 120 my FE has been :

1. Accent CRDi - 22 kpl
2. Maruti Zen [Esteem engine] - 17 kpl
3. Maruti zen [normal engine] - 19 kpl
4. Maruti 800 - 14 kpl
5. Tata Indica - 16 kpl
6. Tata Indigo - 14 kpl
7. Tata Estate - 13 kpl
8. My favorite Maruti Gypsy King - FE ?? whats that..I love to drink like u oh master!
9. Mahindra CJ3B - 120 err..at 12 kph maybe 15 kmpl.. max speed was 80..
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Old 18th February 2008, 16:10   #32
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Quote:
Originally Posted by nitrous View Post
My most economical speed in the 1.3 push-rod ikon is 100kph.
19.75kmpl is what I got.
Yeah..nitrous pushed the car downhill the hosur krishnagiri slopes and used the slipstream effect to go uphill
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Old 18th February 2008, 16:22   #33
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Quote:
Originally Posted by headers View Post
Personally any speed < 120 makes one go to sleep
You must be travelling on highways everyday & going at a constant 120 for quite a while. If us Astra owners got such a drive everyday, then Astras would not be considered as Drunk on Petrol cars. Not to mention being some of the lucky few to enjoy cars built for highways & speed. I get constant 15 kms to a litre on the expressway at 130kmph that too after 10 years!
P.S. - In the rare occasion when i get to drive on the highway.

We city commuters anyway hardly get a chance to even get 80 for a few seconds. And in the stop-start traffic with many gear changes & cold starts for short distances packed with traffic we need every drop of petrol to work. So we are asking this FE question As a few kmph will not make any difference but a higher FE definately will

Last edited by Xehaust : 18th February 2008 at 16:29.
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Old 18th February 2008, 16:24   #34
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In my view, for best FE one should be driving on top gear at such an engine speed at which the engine sounds the quietest without being on the verge of stuttering. For instance, my Petra sounds smooth and absolutely unstressed at 2000 rpm. That engine speed would be the most FE speed.
Beyond 2000, the engine begins to take on a sporty sound. Past 3000, one definitely notices the sound of the engine, and at 4000 rpm, it sounds so exciting, it could never be any good for FE.
Therefore, when your engine sounds dull and bored, its delivering the best FE.
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Old 18th February 2008, 16:35   #35
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O man prabu,
Did you make that commercial for the Bike - Why listen to the music of humans, when you can listen to the music of the gods

On a more serious note, i agree with you. Thats a very good observation, made me realise that it happens in my car as well. And i would like to add that i just love the sound of engines.
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Old 18th February 2008, 21:19   #36
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Quote:
Originally Posted by Xehaust View Post
You must be travelling on highways everyday & going at a constant 120 for quite a while.
Yeah and am bored stiff of it. Thats why i wanna change my car
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Old 19th February 2008, 09:51   #37
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Quote:
Originally Posted by Xehaust View Post
O man prabu,
Did you make that commercial for the Bike - Why listen to the music of humans, when you can listen to the music of the gods

On a more serious note, i agree with you. Thats a very good observation, made me realise that it happens in my car as well. And i would like to add that i just love the sound of engines.

And I simply love the sound of my Petra's engine. Its to die for at 4000rpm. I have managed over 15kmpl on one single highway drive, but never again. Why? Since I discovered the drug like effect of the sound past 3000 rpm. From then on, the best I have managed has been 12.5 kmpl, even on long drives with marginal traffic.
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Old 19th February 2008, 10:56   #38
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Quote:
Originally Posted by Xehaust View Post
Does anyone know at what RPM is the peak-torque of an Opel Astra?
(1.6 Petrol) And what would be the best speed for better FE?
2700 RPM

Quote:
You see, Astra anyways is not an efficient car, but drives & handles like a dream so i drive spirited every once in a while and she drinks petrol like water, so i try to drive economically the rest of the time to make up for it & squeeze a little more efficiency.
Hang on a second Astra not fuel efficient?
I used to get regularly 10 kmpl in Pune city with occasional AC and no I didn't do anything special to get better FE. Just regular driving.
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Old 19th February 2008, 13:08   #39
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I have experimented with different speeds on my Accent..and after a point of time I decided not to follow the manufacturer's suggestion for the gear shifts. From my experiments for the past 5 months the following is what I do to get the max mileage out of my car:

1. Accelerated smoothly upto 45 kmph in third gear and shift to 4th
2. I dont stay much in the fourth gear as I shift to the fifth if I cross the 55kmph mark

The sweet spot for city driving is hard to say City mileage ranges between 9.8 to 11.6 kmpl

The sweet spot for highway driving for my Accent is 95 kmph where I may vary the speed between 85 kmph and 110 kmph (if I had to overtake!). The mileage that I have obtained through this with 75% AC is 17.6kmpl

Another factor is that I stick to HP Power or HP normal (didnt spot a diff in mileage..but HP Power is smooooth for sure!) for the best power delivery and mileage.
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Old 19th February 2008, 13:11   #40
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Perhaps this link will help. There is a widely accepted graph (used by EPA, OECD, and IEA) which gives fuel economy at various speeds. The graph is in miles and to convert into km, multiply by 1.609344.

Tips to improve your Gas Mileage
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Old 19th February 2008, 13:18   #41
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Also, to convert miles per gallon (mpg) to km per litre (kmpl), mutliply mpg by 0.4251 to get kmpl.
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Old 19th February 2008, 13:39   #42
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I wonder how can such a graph can apply to all vehicles.
If you have something which is breadbox shaped, like the gypsy, you would get better mileage if you do 60kmph.
A high power high torque GT like the BMW 645D supposedly gives best mileage at around 60mph(96kmph).
Depending on the torque curve of the vehicle and also the coefficient of drag(cg) your best mileage speed will vary.
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Old 19th February 2008, 13:58   #43
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If you see the figure, you may find that 35-55 mph (or 55-90 kmph) seems to be the most economical speed for a car. In 2005, the IEA/ECMT/OECD had brought out a report `Making cars more fuel efficient'. It had noted although diesel has higher FE, the effect of vehicle speed on fuel economy is larger for diesel vehicles in comparison to its effect on gasoline vehicles. The diesel engine’s fuel economy benefit over a gasoline engine on the same vehicle is smaller on the high-speed test than on the low-speed city cycle. At 150 km/hr, the direct injection diesel’s fuel consumption advantage over petrol is typically only 15 to 18%, as opposed to 25 to 28% on the city cycle. (This corresponds to a fuel economy advantage of 18 to 22% at high speeds compared to 33 to 39% at low speeds.)
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Old 19th February 2008, 14:08   #44
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Quote:
Originally Posted by nitrous View Post
My most economical speed in the 1.3 push-rod ikon is 100kph.
19.75kmpl is what I got.
that's all i have to say

Now seriously is it possible to get that kind average from IKON. I never take my car beyond 2000 rpm per gear( Only on NH-8 you get to know that machine can go beyond 60 kmph). I get around 14 to 15 from both my cars Ikon and XETA
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Old 19th February 2008, 14:13   #45
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Quote:
Originally Posted by vasudeva View Post
In 2005, the IEA/ECMT/OECD had brought out a report `Making cars more fuel efficient'.
This report is priced and may not be available for free download.

From this report, apart from the biggest factors-congestion, AC use, vehicle weight and power, I have taken out some factors that reduce FE (many may be known and obvious) but some may be useful to the members:

Short trips means high consumption. Short trips at cold ambient temperature result in the greatest fuel economy penalty. During the first kilometre of travel from a “cold” start even at 20°C, the fuel consumption is up to three times higher than with a fully warmed-up engine. Both the OECD and EPA reports suggest a fuel consumption increase that is directly proportional to (30 – T)°C, where T is the ambient temperature, and inversely proportional to trip length. (Above 30°C there is no change to fuel economy.) Even with the engine fully warmed up, low ambient temperatures reduce fuel economy due to greater heat losses from the engine and increased drive train and tyre friction. The OECD analysis suggests a change of the order of 0.2% per degree decrease in ambient temperature to 0°C and 0.5% from 0°C to -20°C. The cold start fuel consumption factor is much larger, but trip distance dependant.

Wind and precipitation can act to increase fuel consumption, but they have a relatively small average effect, partly because high wind conditions or heavy precipitation are relatively infrequent in most places, and driving is also typically reduced under these conditions.

Extended idling or “creeping” forward at very low speeds. Diesel engines have lower idling penalty than petrol.

Twisting roads, unpaved surfaces and mountainous regions. Effect of winding roads and unpaved surfaces typically increases overall consumption by 2 to 5%.

Moderate gradients (less than 4 to 5%) impose very small penalties on fuel economy since much of the energy lost in climbing is recovered in the
downhill phase of driving. Steeper gradients, involving operation in a lower gear, can have large effects since the climbing energy is also dissipated in braking downhill.

Modest penalty of vehicle maintenance on fuel economy are associated with dirty air filters, use of higher viscosity engine/transmission oils, “sticky” brake linings, incorrect tyre inflation and wheel alignment. Dirty air filters can cause fuel economy to decline by up to 6% in older vehicles, but has smaller effects on modern vehicles with “closed-loop” air fuel ratio control. Surveys of vehicles in the US found tyre pressure reductions were stated to affect fuel consumption by 2.5 to 3% per psi reduction from recommended levels.


Driving Style: Shift up as soon as possible. For petrol/LPG cars at a maximum of 2500 RPM, for diesel cars at a maximum of 2000 RPM. Maintain a steady speed, using the highest gear possible (rpm of 1200-2500 rpm can save 10% fuel on average). Look ahead as far as possible and anticipate movement of surrounding traffic. When slowing down or stopping, decelerate smoothly by releasing the accelerator well
ahead of time and coasting, leaving the car in gear.
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