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Discussion Starter #1 (Edited)
A lot of people (including myself) have said that its completely pointless to put 91 or 93 octane in your car thats tuned on 87. The reasoning is just because you have nothing at all to gain. Well if thats true then why do people 100 octane in sports cars that are tuned on 91? From reading different threads I know that there is a performance increase in the Elise (91 octane tuned) if you put 100 in it. So is it just that only sports cars can get any benefit from this?
 

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I don't know about other cars, but my increased performance on 100 octane, which is significant, is because I have two available engine maps, one specifically designed for 100 octane.
 

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+1

Bingo! ...It's not just the Octane, but having the tuning/mapping to also go along with it.
 

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Cars with higher compression ratios heat the air/fuel mix up more before ignition, and so need a higher resistance to ingniting early. Higher octane numbers simply mean that the air/fuel mix will resist igniting at higher compression ratios, and doesn't imply that you get more energy out of the mixture.

For example, ethanol's octane rating is around 116, but ethanol has less energy per volume than gasoline so doesn't itself result in improved performance. People often use higher octane gasoline to prevent detonation when artificially increasing the compression ratio such as by supercharging or turbocharging, which is one reason it's often associated with higher horsepower despite not actually providing greater power or efficiency itself.

John
 

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Discussion Starter #6
So basically at gas stations that have both 91 and 93, I might as well save my 90 something cents on a full tank and just put 91 in it since that what the Elise is tuned on right?
 

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I read a study somewhere that gave pretty strong evidence that even a regular stock street car can benefit on the track from higher octane, especially on hot days. I don't remember the link, but I'll see if I can find it. The car they tested was a c5 vette, I believe.
 

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I read a study somewhere that gave pretty strong evidence that even a regular stock street car can benefit on the track from higher octane, especially on hot days. I don't remember the link, but I'll see if I can find it. The car they tested was a c5 vette, I believe.
That solely depends on the tuning of the ECU.

Charlie would be the best possible person on here to answer that question about the Lotus... and he said only the supercharged variants "might" benefit from it :shrug:
 

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I read a study somewhere that gave pretty strong evidence that even a regular stock street car can benefit on the track from higher octane, especially on hot days. I don't remember the link, but I'll see if I can find it. The car they tested was a c5 vette, I believe.
You'll get the benefit of additional knock resistance if you run high octane gas. This is really good if you're tracking the car as it provides some additional protection, but it probably won't affect performance too much unless you're tuned for it. "Some" cars ECU's are designed to optimally run on 93 octane. In Cali, the highest we get is 91 octane. So adding in some 100 octane might bump performance a tad compared to 91 octane.
 

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I read a study somewhere that gave pretty strong evidence that even a regular stock street car can benefit on the track from higher octane, especially on hot days. I don't remember the link, but I'll see if I can find it. The car they tested was a c5 vette, I believe.
From the article you linked:

" So...how much octane do you need?

Only enough to keep your Corvette’s engine out of detonation. More than that offers no performance advantage."
 

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I never meant to imply that the added power was anything other than the added knock protection, I was just surprised at the amount of knock most street cars seem to get when run hard. So, at the track (especially here in socal) it seems that if you want the maximum performance out of your car, you should run 100UL.
 

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The S has an aggressive knock map, so running higher octane might help with that, and if it does, you'll get more power , the NA cars aren't as aggressive.
 

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Charlie,
So for those of us running your tune on the Sector 111 Katana s/c what is your recomendation.

And by the way YOU ROCK!!!
 
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