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Alright well i have been reading some articles and i was wondering if i should you 91 octane gas instead of 87 in my 03 civic. There isnt any mods beside intake done to it. I was mainly wondering if it would improve or decrease my gas milage and if 91 would do anythign to damage my motor?

 
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other than being a waste of money, and ur gas mileage will go down, i have 108k miles and i just use midgrade, seems to keep the gas mileage up better than 87

 
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I don't know who deleted this but I am putting it back.

Just ask the easy button.

 
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instead of reading articles i think you should read the owners manual :P
if its vtec i believe you use 89octane.. but if its non-vtec 87octane

READ the MANUAL

 
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It is all in the manual and to quote the manual it says "87 octane or higher"

Use 87...

 
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i use 89 and i drive an automatic lx

 
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I seem to get better mileage on 89 than 87. I ran 93 for like a month but that was just a waste and had poor mileage as well. 87 is fine but run a good fuel system cleaner every so often. I do this every 2 oil changes and my mileage is great comparable to Gearbox who is the 7th gen guru.

 
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yea 93 is a big waste of money... i use 87 from chevron.... and i see no difference in power from 87 to 93... as for gas mileage.. i think it depends how you drive the car...

 
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i heard.. if ur car doesnt recommand 91 oct dont bother using it. i heard it ruins ur injecttors as well but i heard it helps .. close knockin on the engine.. hahahha..

 
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Since this continues to get longer:

This topic comes up ever couple of months and because most of the members are kinda new they don't remember it or the post some worthless crap and move on.

I am quoting myself from one of the other threads, the quote is in reference to one of the original octane threads.