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Old 25th May 2007, 14:29   #91
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Hi guys,
I own a Fiesta 1.6 sxi for the past 2 months. I've been filling up unleaded fuel from IndianOil since then. The Ford manual prescribes 91 octane fuel.
Not sure if what I have been using is 91 octane fuel. I got this doubt because i saw a BP bunk selling premium petrol as '91 ocatane petrol with additives'. When I asked the dealer, he was not sure if the ordinary fuel was 91 octane or not.
Any suggestions?
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Old 25th May 2007, 15:16   #92
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Originally Posted by appuchan View Post
I dont have equipment to try it out. But one thing I can say from Physics is that Air Drag is proportional to the square of the velocity. So if air drag is say 200 N at 80 kmph, at 100 kmph it should be 300+ N. No small amount this. Note that rolling drag is considered as constant across speeds.
How did u get those numbers...it depends not only on density but also other factors too....

To be precise, There is something called Stokes Drag (eg Drag at lower speeds/smaller particles) and drag at higher speeds which can be explained for car... Dont ask me Stokes Drag as I have to refer back to my physics book but i do remember the drag for a car....

Drag at higher speeds = 0.5(Coeff. of Drag)(Density of air)(sq. of velocity)(Area of Cross-section)

The coefficient of drag itself is quite complex, it depends on factors like it is (generally 0.25 - 0.35 for a car)...

Hence it maynot be that significant at lower speeds below 100kmph compared to 140kmph....The automobile/car is aerodynammically designed to lower the drag at speeds below 100kmph....

Abhi
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Old 30th May 2007, 18:28   #93
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@vnabhi,

The normal unleaded fuel is 87 octane.
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Old 30th May 2007, 20:45   #94
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Originally Posted by risga View Post
@vnabhi,

The normal unleaded fuel is 87 octane.
Thanks risga. Then I shall switch to Indian Oil premium petrol.
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Old 31st May 2007, 02:29   #95
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Why does a 100 hp econo sedan need 91 octane? :-s
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Old 31st May 2007, 09:57   #96
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Quote:
Originally Posted by akroy View Post
How did u get those numbers...it depends not only on density but also other factors too....
...

Drag at higher speeds = 0.5(Coeff. of Drag)(Density of air)(sq. of velocity)(Area of Cross-section)

The coefficient of drag itself is quite complex, it depends on factors like it is (generally 0.25 - 0.35 for a car)...
I have quoted an approximate figure based on the project I did in my college 10 years back. May not be exact ones. In your equation itself it shows that air drag is prop to square of velocity. So I dont know what is the dispute. Other items being constant, for a particular car, the figures will be similar to that quoted by me.
Quote:

Hence it maynot be that significant at lower speeds below 100kmph compared to 140kmph....The automobile/car is aerodynammically designed to lower the drag at speeds below 100kmph....

Abhi
Significance at lower speed or higher speed was not the issue. Difference of Drag between speeds was the one. As I mentioned Drag at 100 kmph compared to 80 kmph will be significantly higher. And for much higher speeds many other things like wind speed, etc come into significant play.

See the link below for sample charts

Velocity and Air Drag

Last edited by appuchan : 31st May 2007 at 10:01.
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Old 31st May 2007, 11:59   #97
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IOC's XtraPremium is 91 octane.
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Old 4th June 2007, 14:19   #98
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Hi GTO!!
good write up man!! you put it all in one place! you were absolutely right about the shutting off the engine bit during long idling. the hyundai manual states that if the waiting period as more that 3 minutes, the fuel consumed is equal to 1 kilometer worth of travel!! something to think about isn't it?

According Maruti manuals (for Esteem) this interval is 60 seconds - they suggest to switch off if you would be idle for than a minute

ArijitM
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Old 4th June 2007, 14:36   #99
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Nice one GTO.

What about filling fuel early in morning or at sunset to get marginally benefits? (read in our forum)

Yes.. That's an interesting proposition .. We pay by volume .. afternoon volumne would expand charging more money giving less fuel

Also, some service engineer suggested to run as close to full tank as possible ... This would be lead to reduced vaporisation as less space for air inside the tank...
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Old 20th June 2007, 15:43   #100
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CAR - RELATED MEASURES

The honest petrol pump: Considering the high amount of fuel adulteration and other fuel-industry malpractices, we highly recommend you to choose the right petrol pump. Tampered meters that result in under-filling, misappropriating bills and selling adulterated fuel are some of the most common malpractices. Company-owned filling stations are the best option, though there are some honest privately-owned petrol pumps also. Look around and opt for an honest reputable petrol pump. This alone can account for upto a 10% difference in your fuel efficiency.
Few monts back I saw one TV show saying that attendants at petrol pumps tries to full the tank even after automatic stop. Each time they pull the lever after autostop, you are paying more for less fuel.

Is it all true, please guide.

After watching this show I also observed this closely and asked them to stop the filling on autostop. These guys spends their time watching the figures go round instead of watching the nozzle.
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Old 25th June 2007, 15:26   #101
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Thanks for such a informative write-up.

By the way I would like to ask one question here. I have seen that use of high octane fuel like Speed or Extra Pemium adds on to mileage to some extent. But I have been told that it affects the engine of low-end cars like my Wagon-R badly as it is meant for expensive cars with high-end engines with higher rpms and things like that. Also if i fill up once from HP and then from IOC and again go back to HP does it affect my FE. Actually I have both HP & IOC pumps in my vicinity and fill up from either as per convinience.

Let me know your views on the same.

Tathagata
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Old 25th June 2007, 15:39   #102
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Filling high-octane fuel on a Wagon-R is a waste of money. Dont.
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Old 25th June 2007, 16:11   #103
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What about using premium Diesel in Swift VDI is it worth?
Never followed in 2 wheels but sure like to see the FE of my VDI following these rules.
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Old 25th June 2007, 18:33   #104
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What about using premium Diesel in Swift VDI is it worth?
Never followed in 2 wheels but sure like to see the FE of my VDI following these rules.
Not really necessary in Diesel. The additives in the so called "Premium Dielsel" are there only to keep the 'waxy' elements from accumulating and causing problems in the injectors etc. You could as well add a bottle of the injector cleaner every so often to a tank-full of normal diesel. Just buy normal diesel from Shell, instead of the hyped-up "Super"s and "Extra"s.

Depending on your daily driving distance, you would need to do it once in 2-4 months.
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Old 25th June 2007, 22:09   #105
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Additive fuels like Speed petrol and Turbo Diesel do not give great advantage in fuel mileage. They have calcium additives and this leads to clogging on injector tips. Getting a better mileage depends on few important things like proper tyre pressure, proper maintenance of engine(less friction, feather like acceleration, proper shifting of gears etc). Regarding fuel , instead of filling additive fuel , please fill fuel in a proper fuel station which is properly covered ( water sepage) and reputed.
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