91 vs Other Octane

Ok, so I was wondering, in my neck of the woods, we have QuickTrip's with "guaranteed gasoline" which is 91 Octane. We also have shell with their "V-Power" and Exxon/Mobil's Super, both of which are 93 Octane. I
personally have not tried the difference of running my car on both of these options, I ALWAYS buy 93, but once I was forced to buy 87, and I have heard they can run it, but the stock ECM will detune to accomodate the lower grade. I am wondering, if this +2 Octane even makes a difference in modern multi point fuel injected engines; namely my LT-1 powerplant. Can any power gains be had from buying 93 over 91, or even adding octane booster to my 93? Any thoughts or words of experience?
The Freak
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Octane does not increase an engine's power. Rather, engines with higher compression (thus, more powerful) require higher octane gas in order to prevent detonation and preignition. With computer controlled engines you will notice a decrease in power with low octane due to the knocking (preignition / detonation). The octane rating of a fuel is a measurement of its ability to resist detonation and preignition and has nothing to do with how many ponies can be generated by a certain amount of fuel. Power is determined by the temperature change when the fuel lights off, the hotter it burns the more the hot gasses expand and the more pressure it exerts on the pistons.
With octane, if the car does great on 91, no detonation or preignition, then 93 won't help. If you notice the 93 gets you better performance, then 91 wasn't good enough and was probably kicking in the knock sensor. If you are ever forced to use the 87 again I would buy just enough to get to another station and then fill with higher octane. I would also stay off the peddle. The control module can compensate for some of the preigniton / detonation but maybe not all of it. The end result of too much of too much knocking is melted pistons, the higher the revs the more susceptible the engine.

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Ken wrote:
In a nut shell, use just enough octane to keep the engine from pinging. Any extra is just a waste of money.
Here's what you should really be concerned with:
http://www.toptiergas.com /
Patrick

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snipped-for-privacy@aol.com wrote:

Actually the octane issue is not exactly that. You need the amount of octane the engine was designed for. This should normally allow you to get performance without detonation WITHOUT needing to retard the timing.
--
Cy Welch
89 Camaro RS 5.0 TBI
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I notice a big difference in gas mileage and performance. Maybe I'm just sensitive that way but I only use 92-93 octane. You gotta feed the beast.!!!!
-CCC
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It's best to set the spark curve and time the engine with the lowest octane fuel that won't pre-ignite under load. Even though there's absolutely no difference between gasoline's potential energy based on octane; the resistance to ignition (octane) affects combustion timing without changing spark timing. There's a lot more to it (waaay lot more) but we can try something else. Maybe somebody here can do a simple study. Let somebody else fill your tank without telling you what grade fuel it is and, then, you make one-line notes about your experience. Should be the same person, same gas station, same driving conditions over several tanks. Use each tank down as close to "E" as you comfortably can and then fill up again with a secret octane. My sit. won't let me do that right now but would be interested to see outcome. Heck, even throw in some 93. Might be surprised by the perceivable difference in drivability and mileage or lack thereof. Regards, Drink

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James Drinkwater wrote:

    A item often over looked in octane debates/questions on recommendation is: Not all gas is the same.
    The rating method in the USA is RM2. Gasolines meet the Minimum required mathematical formula for the rating they are given. Some may Exceed that rating. An Example is shells V-power. In the part of the country Im in it will be anywhere from 93 to 95 Octane, and possible as high as 97 Octane. That's according to a pamphlet shell put out at the filling stations last year. While it would be fine and dandy to use in Electronic Fuel Injected vehicles that map out the best fuel and spark curves off the sensor info, trying to tune in a High Performance Carburated car on something with that much swing would be impossible.
    My favorite fuel is being phased out around here, that is Sunoco Ultra 94 Octane. Which is what I tuned all my Performance V8's for.
    A question that I always get asked is: what should I run in my car? Although with todays fuel prices that question has been replaced with: whats cheep and safe?
    I always recommend to my customers with stock vehicles to find a good gas station, and stick with it. Do not go lower then the recommend minimum octane for their cars (usually 87 or 89), and that it never hurts to use higher rated fuels. The premium fuels usually have the better additives, such as fuel system cleaners, while the lower octanes don't.
    In the end does it matter? Yes. From what I have seen the people that spend the extra on premium fuels have less injector failure, less issues with clogged injectors, less carbon build up issues, less over all fuel systems issues. It's always the customer that run the cheep crud that come in with fouled plugs, carboned up EGR systems, and clogged or bad injectors. They are also the same customers that won't listen to me about adding a can of fuel system cleaner to their tank with a fill up every X number of miles.
    As for Camaro Cowboys car, does it need the premium fuel, maybe not. Is he hurting it? Not at all. Is he wasting his money, no not really. If you can afford it, with out a major effect on your budget, go for it. Charles
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I had a 96 T/A for a few years and recently came across a deal on a 99. When I had the 96, I only ran 91 octane or higer. Once my girlfriend took the car out and put gas in it while she was out. I noticed an immediate difference. The car was a six speed and taking off with the lower octane was not as easy. It wanted to stall out when letting the clutch out. The 91 never gave me that problem. The gas mileage was better with the 91 too. I have not tried changing the type of gas I use on the LS1 motor yet, but I expect similar results.
On Sat, 28 Oct 2006 15:51:13 GMT, Charles Bendig

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