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[Modified by Bryant, 10:16 PM 2/14/2003]

 

No, don't run lower octane. Higher octane will help prevent you from having any detonation problems. You could probably get away with using 89 every now and then, but I wouldn't.

cyber13


[Modified by cyber13, 11:04 PM 1/25/2002]

 

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[Modified by Bryant, 10:16 PM 2/14/2003]

 

how would your internals be fried? hmm correct me if im wrong, but higher octane lets it burn slower which keeps cyl. temps down apposed to lower octane which temps would be higher due to "flash burning"

 

tell your friend that hes smokin some good sh*t

 

No sh*t, puff, puff, give................

 

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[Modified by Bryant, 10:17 PM 2/14/2003]

 

Higher octance really only benefits high compression engines.

If you 10.0:1 or higher NA, then 91 octane is recommended.

Turbo, NOS, SC, all can benefit from higher octane levels.

Aggressive chips, and highly advanced timing can also benefit from higher octane levels.

Stock engines that are less than 10.0:1, can use 87 or 89 octane without a problem.

 

I have mentioned this many times and never got a straight theory as to why this happened, but here goes:

I always ran 93 on my b16, and I had a hard time getting the thing into the 14's. I switched to 94, and would always run deep in the 14's.

After experimenting for weeks, I was sure that it was in fact the Sunoco 94 that made my car that much faster. I don't know why, it's supposed to be all right on 91 octane, but there you go.

Anyone have any theories? It was a stock J-spec b16, as far as I knew. Was there a couple pound of carbon deposits in there raising my compression? I don't know. Anyways, I suggest to everyone to test their car out with different grades of gas. You might have extra power in there.


[Modified by Lsos, 11:22 PM 1/26/2002]

 

Higher octane fuel doesn't burn slower, it's a common misconception. The hydrocarbons used to make gasoline will oxidize, or burn, at virtually the same rate, given the same conditions. The controlling mechanism of burn rate or flame front travel is the ammount of oxygen in the combustion chanber available to react with the fuel. More oxygen means a faster flame front. That's whay a high octane fuel is only needed if your running high levels of boost (more oxygen) or high compression (more oxygen).

 

Everything made sense....except the last sentence.

This completely didn't fit into that paragraph

Anyway, octane rating is just resistance to detonation. Higher boost and compression increase the likelyhood of detonation, hence the need for better gas.
I think the reason high octane racing gas is unsuitable for street engines is not that it will burn your pistons or anything, but becasue they don't put any necessary additives into it, like they do in street gas.
I think they might add some stuff, too, like lead.



[Modified by Lsos, 5:29 PM 1/27/2002]

 

Using a higher octane gas than is necessary won't cause you ANY problems. The higher octane will be wasted since the engine can't take advantage of it, that's all. Plus, you'll be paying a higher price, so you'll be wasting your money, too. Using a lower octane than is necessary MAY cause you problems.

If in doubt, go with the higher octane.

 

boosting your octane level will do nothing except waste money, unless you are currently using octane fuel that is too low for your setup. So if you don't know then experimentation along with a keen ear is necessary.

Octane is commonly defined as the "resistance to detonation," the determining factor of how much compression/pressure the mixture can handle without spontanoeusly exploding (aside from the normal, slower, spark induced burn). So of course if your engine is a higher compression, 10.0:1+, then 91+ octane is recommended.

If your car has a knock sensor, then it'll automattically retard the timing to compensate, and avoid the engine killing detonation from the too low grade fuel. So in that case, increasing the octane will yield a performance gain. Any octane higher then necessary is just a waste o money. I dunno, can you disable the knock sensor to do the 5th gear/slight incline/ping test?

I'm not so sure that the higher octane burns slower tho, seems to be some controversy there. You'd think that if the fuel composition is changed, then the burning characteristics must...

Mr. lsos, did you switch gasoline brands when going from 93-94 octane? Maybe sombody's lying.

d

 

Yes, I did switch gasoline brands. I went from Mobil 93 to Sunoco 94.

FYI, I later mixed in a gallon of racing 108 to ten gallons of Sunoco 94. It made no difference.