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Discussion Starter #1
okidoki, so the recommended fuel is 91 right? Well, I usually put in 89 or 91 depending on where I can get it, and the occasionally wallet lightening 93. But I've also read here that fuel technology is more advanced now, and that todays 91 is the equivalent to the 80's 91 octane. But anyway, why is it that even if I drive my car harder, I get better fuel mileage with 87 octane over any other. I usually put in Exxon, but notice a slight difference in power between other brands. I've kept this experiment's independent variable as Exxon gas. So all I've been using lately is Exxon. I've gotten about 5 more mpg with 87, than 93. And almost nothing more with 89. When I noticed that I was getting better mileage with the 87, I started to drive it harder, and thats when I came up with the average of about 5 more mpg. Am I imagining this, or is there a logical explaination??
 

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because your car is tuned for 87...

by pumping 91, the only thing you are doing is flushing money down the toilet
 

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^ Hit the nail on the head.
Use the lowest octane gas that your engine will tolerate without detonating/pinging.
 

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Predwolf said:
The higher the Octane, the slower the gas burns.

In a nutshell.
Ding Ding Ding!!!!

The higher octane guards against precombustion of the fuel. How? Must have inhibitor to make it ignite and burn slower.

My car would not know how to act with anything but 87 octane in it.

JOhn
 

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which is the same reason i run 91 in all my cars (and wish i could get higher). The two turbo cars benefit very much at higher internal pressure from running higher octane fuel. plus both use knock sensor equipped motors that advance until they have to retard. and the 20v is also in the 10.5-1 compression range. it probably doesn't do well on 87 (around here the std grade is actually 85 :( ) and it does have a knock sensor as well.

Tho IIRC, my old 85 16v ran better on 91 than on lower grades. seemed happier and smoother. plus at a cost diff of a buck or two per tank, i never worried much.

i for one can't believe that most owners out there with those high-output v6 family sedans are using the 91 octane require by their high-compression motors that make 250-300hp...

oh well. we'll probably go over fully to hydrogen or electric long before we ever get better than 91oct around my area
 

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Filling with mid-grade will do nothing unless you've tuned for it or have so much carbon & crap built up that you need it as a crutch. Then you can brag that you use mid because your engine runs so badly because of neglect that you have to spend more to keep it from knocking.

Octane booster raises the octane negligibly. I've heard maybe .1 or .2 points (depending on the amount of diluting fuel). It's a huge waste of money.

Your mileage suffers because the higher octane doesn't combust as easily, so in essence, you're getting less power from the worse combustion.

Read up by searching prior threads on octane or boosters. They're discussed here every couple months.
 

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Discussion Starter #10
that reminds me somehow, but I also get a lot of back fire when I use 93. It doesn't happen when I use 87. :thumbup Back fire sounds cool though!!!
 

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Octane booster have been tested over and over and proved that they do anywhere from nothing to very little (not enuf to be worth the money. get to mixing race gas or other solvents if you need higher Oct for some reason). However things like Techron in a bottle are great detergents. I run a bottle through every spring on the cars that sit for the winter.
 
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