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I know I read over and over that the levels of Octane used in cars these days doesn't matter. For the last 3 fill-ups I decided to try the mid-grade unleaded which is 89 octane. In my region you can get 87, 89 and 92 grade gasoline. Well folks, my MPG has actually gone up some to 27.2 average from 26.7. The most noticable is the throttle response. I do notice a more reactive throttle response. In order to see if this is just my imagination. I am going to switch back to 87 octane for the next 3 tanks and see.. Anyone else do this? or use a higher grade fuel in their Fusions/Milan? :?
 

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Octane does matter when it comes to detonation .... The more octane, the less detonation meaning the less retarding of the timing.
 

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i really think its just a placebo effect, the milage isnt that incredable and throttle can be u just thinking that so , eh save money
 

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when i fiirst got my car, i always used regular grade and would only get around 350 miles to the tank, the past few times, i've been using high grade and now i get around 450... i don't really notice a difference in performance though... anyone else notice this?
 

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Modern cars have computers which can figure out what octane you are using. Up to a point, they will advance the timing more on higher octane gas, but only up to a point. You coult put 130 octane av-gas in it, and it would run crappy because the timing couldn't advance enough to start the gas burning.

Remember - higher octane means slower burning so the engine can fire the spark sooner (advance the firing) allowing a longer burn cycle which can (if the car is capable and most new cars are) yield higher power. Beyond the limits of the computer, higher octane is just a waste of money. I would believe 89 or even 92 would yield some better performance and mileage than 87, but somewhere between 89 and 92 the engine reaches its maximum advance capability and the rest, as they say, is wasted.
 

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Since the purchase of my SHO the only fuel I use is Sunoco 93 octane. My 93 SHO always ran great and when I traded it, it had 187,000 miles on it. I never had a problem with the fuel injectors or any other fuel related parts.

Along with the fuel I was very good about taking care of maint. items such as filters and fluids.

Over the last 3 months I have put 4200 miles on my fusion and I have averaged just under 29 MPG's with a almost 50/50 highway/city driving ratio.

I am not saying that the fuel is the only reason for good mileage and a long lasting engine, but the couple times that I have used 87 octane fuel my car does not run nearly as well.
 

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130 octane av-gas
Avgas is 100 Octane. The octane wouldnt necessarily make it run shitty, but the lead will. Avgas is leaded to help lubricate the valves, at least thats what i've been lead to believe. I used to only run premium in my old volvo turbo. Switched it to regular after Katrina. No change in mileage or power. No detonation. Ive been averaging bout 27mpg in my 5spd fusion on regular. Unless my mileage goes up to 30+ around town I see no need to run premium
 

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One thing that hasn't been mentioned here is that the higher octane gasolines frequently contain more of the cleaning agents and detergents than the 87 octane. You can literally "drive your engine clean" by using higher octane for a while. This benefit frequently makes the car run better, and for a while after you switch back to 87, you won't notice any difference.

BTW - in my old flying days we used 130LL avgas in turbocharged engines. LL means "Low lead" which, as posted here, is to lubricate the valves.
 

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With only a .5MPG improvement, it's more expensive to run mid-grade.

As far as increased power from simply adding higher octane fuel, that for the most part is a myth. There are actually a few cases where that can decrease engine power. Your best bet is to just run the 87 octane that the engine was designed to run on.
 

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87.

Do anything else and any "gains" you get are all in your head.
 

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not worth it. Your car is tuned for 87. It has a set spark table, and will sense for knock and retard timing if it occurs. You can put 130 octane in it, and the tuning will still be for 87. It is possible to use power using a higher octane fuel, since it burns slower, and the engine is not tuned for it, there is a small percentage of the fuel that is not even burned.

If youre on a stock tune, just stick with 87 octane.
 

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there are lots of variables to consider. In general higher octane fuel burns slower, so if you can't maximize the extra octane with advanced timing then you will likely lose power. But if your engine can run a bit more timing then you can make more power overall. Given that some guys on here have reported pinging on their engines then I'd recommend running a bit more octane, nothing crazy, but perhaps 1-2 points. If you get pinging the engine may run a more conservative timing map, if you run a bit more octane the engine may be inclined to run a bit more timing. I think a mid-grade octane around 89 is a good idea, 91-93 would be a waste unless you can take advantage of it with more timing. I haven't had any pinging on my car but it is relatively new and we haven't had hot weather in my area since purchasing the car. In hotter climates it probably could help.
 
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