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Old 24th June 2005, 16:33   #1
AGP
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Default Does Higher Octane Petrol need additives?

I saw in one of the threads about 98 octane petrol available at Reliance petrol pump, Mumbai. I was so passionate to test it that I spent 2 hrs. on bike to locate the petrol pump. Then I filled up 10 ltr petrol in my ambition bike. I don't know whether it was with addities or what? But what I found is knocking frequently. I thought it might got mixed with the older 91 octane Xtrapre.. petrol. But knocking was continued till I used all the petrol. Then I filled up 91 octane XtraPremium which i was using previously. Immediately I found the difference, my bike became much smoother. So does the bare 98 octane petrol wihtout additives really caused knocking?
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Old 24th June 2005, 19:36   #2
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AGP

Your bike has been built keeping lower octane rating in picture. So it has been tuned that way. To ensure your bike runs smoothly on higher octane rating, several changes need to be made. Primarily, in this case, increasing the Compression Ratio. You might also need to change certain settings in the ECU (in case of cars or bikes with one) as well as ignition timing.

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Old 24th June 2005, 20:02   #3
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@Revmaster, Why should the bike knock with higher octane fuel? Knocking is caused by pre-ignition of charge, fuel detonating before flame wavefront reaches it. Higher octane slows down process of detonation. So, I am wondering why his bike would knock with higher octane petrol. I thought, it would cause imcomplete combustion in his case. I remember, there are two types of knocking, but not able to recall which is the other type. May be you can help.
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Old 24th June 2005, 23:03   #4
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AGP,

dude - i have heard the same problems on bikes filling up reliance 98 octane. strangely cars dont have the same problem...why i wonder??

and i think reliance have now stopped 98 octane petrol , thats wat i was told last time i went there !
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Old 24th June 2005, 23:29   #5
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@RX 135. One of the reasons i can see is the improper quantity mixture of additives or an unwanted additive (remember, Reliance is accused of providing spurious fuel, even to PSU oil cos. in the past) could be hampering the ability of the engine/injectors to work at optimum capability.

Additive equipped fuels, including some from PSUs have been known to reduce fuel-pump life. My mechanic since years keeps warning me every now and then to stay away from additive equipped fuel available at petrol bunks, and keeps suggesting that i add an external additive to 87RON fuel.

The knocking question is an interesting part.Yes with a higher octane rating than what the engine can accomodate, the only scenario that emerges is an engine running rich. Read Dom's thread on high octane fuel here:

http://www.team-bhp.com/forum/showthread.php?t=2166

Should the engine knock? Theoretically no as you rightly mention. Its a question given AGP situ, would love answers to. Maybe someone around can provide answers. Meanwhile i'll try and get back to you with a reason to the problem as well.

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Old 27th June 2005, 13:21   #6
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I haven't spent enough time thinking over it, but I too suspect fuel quality problem. Frankly speaking, it seems like a remote possibility, since I know couple of guys who have filled up at that Reliance petrol pump.

@AGP, was it knocking or was it misfiring of your bike? Misfiring can probably be explained (?) than knocking.
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