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Old 5th August 2006, 12:24   #16
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Yes, no problem to fill xtrapremium when tank is half full of ordinary. Actually to test it, this may be a better way. I always fill when tank is at 40-50%. Then I alternate between normal and xtrapremium.
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Old 5th August 2006, 12:59   #17
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If the car is designed for lower octane fuel, then there is no real performance or FE advantage of using higher octane fuel. Following link has good explaination about this

http://www.straightdope.com/columns/041008.html
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Old 5th August 2006, 13:02   #18
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Quote:
Originally Posted by hondadude
If the car is designed for lower octane fuel, then there is no real performance or FE advantage of using higher octane fuel. Following link has good explaination about this

http://www.straightdope.com/columns/041008.html
Agreed, that is why I said earlier also that it all depends on how the engine / management system takes it. One can always try for a couple of tankfuls and see. Mostly very few cases of any adverse effects have been reported (other than from bad premium fuel itself).

Also if one notices, civic compression ratio at 10.5:1 is the same as international. So it should certainly benefit from higher octane. In case of OHC, they had actually lowered the compression ratio. IMO any engine with compression ratio higher than 8 or 8.5 would benefit from higher octane petrol. Another reason is that when speed was originally launched, regular petrol octane rating was only 83. It was only due to better emission norms, that regular petrol has now moved to 87 and now 89 in metros. Which by the way due to adulteration may be 85 or 87. So now difference between speed / power and regular is only some additives - which may or may not be better for your car. That is why my preference for xtrapremium which is 91 or speed 93/97.

Last edited by sandeep108 : 5th August 2006 at 13:07.
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Old 5th August 2006, 13:32   #19
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Quote:
Originally Posted by sandeep108
Agreed, that is why I said earlier also that it all depends on how the engine / management system takes it. One can always try for a couple of tankfuls and see. Mostly very few cases of any adverse effects have been reported (other than from bad premium fuel itself).
The original poster was asking about Honda City and in its stock variant, it won't help to fill 'er up with premium fuel. It won't hurt either, but if spending more money on petrol is where the happiness lies then so be it
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Old 6th August 2006, 13:13   #20
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I suggest alternate between Regular and Premium Fuels, For every 2 Tank fulls 1 Tank full of Power or Speed 97 or Xtra Premium whichever you run on..!
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Old 6th August 2006, 13:45   #21
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Quote:
Originally Posted by rareone
When i asked him the reason why he said its written in the manual to use 87 Fuel and not the 91 Octane Fuel...
* Did you check the manual?
* Does the manual specifically say "do not use 91 Octane"?

Manuals typically specify the lowest octane rating that is to be used in the car. Using higher octane fuel shouldnt harm the engine, even if there are no benefits - noticeable or otherwise.

OT, used 93 octane in the late 80's in our Chetak and later in my KB100 - engine was running smoother, and FE was better too.

Last edited by condor : 6th August 2006 at 13:50.
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Old 12th August 2006, 15:57   #22
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!!! Well always thought that the ECU has the capability to change firing parameters in real time based on the octane level in fuel sensed. yeah?? When we are talking about a high end car like Optra and the like, I think it must be for sure.
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Old 12th August 2006, 17:09   #23
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Quote:
Originally Posted by gbpscars
!!! Well always thought that the ECU has the capability to change firing parameters in real time based on the octane level in fuel sensed. yeah?? When we are talking about a high end car like Optra and the like, I think it must be for sure.
Does the ECU control the firing timing at all?... I am sure it does not for 800/ WagonR/ Alto!
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Old 14th August 2006, 10:34   #24
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Quote:
Originally Posted by SLK
Does the ECU control the firing timing at all?... I am sure it does not for 800/ WagonR/ Alto!
Why do you feel so? Of course it depends on the mfr., but generally ECU/ECM takes parameters from various sensors (including usually anti-knock, oxygen, etc.) and adjusts timing, fuel, air, etc. appropriately.
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Old 14th August 2006, 12:14   #25
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Quote:
Originally Posted by wolfinstein
I suggest alternate between Regular and Premium Fuels, For every 2 Tank fulls 1 Tank full of Power or Speed 97 or Xtra Premium whichever you run on..!
what good would that do ???
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Old 14th August 2006, 14:33   #26
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Quote:
Originally Posted by sandeep108
Why do you feel so? Of course it depends on the mfr., but generally ECU/ECM takes parameters from various sensors (including usually anti-knock, oxygen, etc.) and adjusts timing, fuel, air, etc. appropriately.
Well I felt so.. just b'coz the ignition system in WagonR/ Alto though is digital is indipendent of the ECU.
The timing is controled by the timing belt.. i wonder how ECU can change that.. unless its a high-end engine like some vtec ...
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Old 14th August 2006, 16:43   #27
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Quote:
Originally Posted by SLK
Well I felt so.. just b'coz the ignition system in WagonR/ Alto though is digital is indipendent of the ECU.
The timing is controled by the timing belt.. i wonder how ECU can change that.. unless its a high-end engine like some vtec ...
I do not think ignition system of any modern MPFI car is independent of the ECU/ECM. The timing setting is usually controlled through the ECU/ECM. That is why many mfr. advt. 8bit/16bit ECM, more than one computer to control other systems. Also most MPFI engines will not knock at all, since the ignition timing is altered. At worst, engine will simply stall. In vtec, it is the valve and other settings also are further controlled.
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Old 14th August 2006, 23:51   #28
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Well, heres somethign Id like to share...The reason why few dealers ask us to stay away from premium fuels is supposedly the additives in the premium fuels affect the cat con. They either clog the cat con or react with the chemical composition that the cat con element is made of. I dont know how much of this is true but have heard several people speaking in the same lines.

One experience I can share is Speed 91 used to leave this pink residue inside my bikes exhaust, donno if you guys have experienced it!!!! My bike dide have a cat con so it prolly wouldnt matter but the ones that come with a cat con might be affected by this residue.
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Old 16th August 2006, 10:42   #29
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That is extremely suprising. With both fuels and cars required to meet BS II/III norms, I am sure our petro companies would not do anything like gumming up cats. But one thing sure odd is that till date all auto magazines are staying away from doing any detailed analysis/comparison of these hyped up fuels.
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