The only octanes available in my area are 87, 89, and 93. Should I pump my tank with half 89 and half 93 to achieve 91, or are there any problems to this that I do not see?
ive never heard of this before. it was always to my knowledge that the higher the octane, the better.
and that knowledge is flawed. Check the gas threads on here even. People who say "well my car is my baby, so I put only 93 in" probably couldn't tell you why they do that. Basically just use octane is required of the vehicle and it's compression ratio. If you're standing at a pump and 91 is offered as well as 93, use 91, you gain nothing from opting for 93.
actually, my grand am got better mileage than my prelude, and i had done more engine modifications to it than to my lude. I hate it, but damn that car was fast.
then why do you get knocks when you put in lower octanes? whats the point of putting a higher octane rather then a lower one? i mean 93+.
Quote:
Originally Posted by Buddhastic
The only octanes available in my area are 87, 89, and 93. Should I pump my tank with half 89 and half 93 to achieve 91, or are there any problems to this that I do not see?
then why do you get knocks when you put in lower octanes? whats the point of putting a higher octane rather then a lower one? i mean 93+.
.
because the lower the octane, the less resistant it is to detonation, so basically by putting lower octane (than recommended) into your car, you risk pre-detonation, or detonation before it should occur. This will usually happen at higher RPMs when things get hotter in the combustion chamber. That is why higher compression engines demand higher octane gas, so the fuel will resist predetonation, and remain stable, if you will, at the higher compression and temperatures until it's supposed to combust.
I believe by putting higher than recommended octane gas in an engine (assuming there are no ignition or compression modifications necessitating it), the higher you go, the less efficiently that fuel is being burned because it's more resistant than to combustion than necessary.
hmm... i guess i see what you mean. but then why is the higher octanes more expensive? just more money to produce or something? i always thought racing fuel would be good.
and how many clicks do you have to advance your timing if you want to take advantage of 93 octane gas?
and like buddhastic said:
The only octanes available in my area are 87, 89, and 93. Should I pump my tank with half 89 and half 93 to achieve 91, or are there any problems to this that I do not see?
Yes you could mix 89 + 93 = 91, or stick to 93 rather than risk 89. Premium is also more expensive because they put all their cleaners and additives in the higher octane gas, then market it as this amazing great gas. More modern sports cars do have the ability to adjust to higher octane fuels by advancing the timing, in which case race gas would be beneficial, but we don't have that ability.
I'd also be interested in knowing how far you could advance timing before switching to 93 but I don't think you can figure that out without a wideband or other diagnostic tools. I have advanced my timing several degrees so I usually fill up with 93 to be on the safe side. Haven't noticed any mileage gain when I put in 91 so I take it I'm burning all the 93 fairly efficiently.
Higher octane fuel is only more resistant to combustion while under higher compression. Using a higher octane fuel won't combust less efficiently. It is still going to combust when a spark is applied whether or not it's 87, 89, 91, 93, etc.. octane rating, if it hasn't already done so from the compression. The point is that you won't have to worry about it combusting before the spark if you use a higher octane fuel.
Higher octane is just plain harder to ignite, whether the source be flame or compression. They can both get the temperature up to where it is hot enough to cause combustion - or not.
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