Bottom line running 87 is perfectly fine in any G and will not harm your engine or fuel system in any way but there is a very slight decrease in power. No noticeable decrease in mpg though because like others have said the ecu accounts for the lower octane and adjusts accordingly. I run both and have for 3 years some guys on here have run nothing but 87 in their cars since they got them

 

Though I have not noticed any real difference in fuel economy and performance between 87 and 91 in my 04, I buy what I'm in the mood for at the time. Usually 91, but sometimes less.

I think I notice more of a difference between 100% gas and up to 10% ethanol. My overall average fuel economy has moved up when using more 100% gas.

In neither case does the more expensive gas really pay for itself

But if I was pushing the car, I would recommend the higher octane.

 

Sell it n buy a hybrid. There's way too many threads about gas..lol it call for premium gas.. use it!

 

It actually doesn't call for it. It's "recommended" but not necessary.

To interpret that as "only run premium" falls along the lines of the mentality that you need to run synthetic oil, or you are abusing the car.


I've run 89 and 93 in my car. No noticeable difference in HP and no difference in fuel economy. I fill up with whatever I feel like when i'm at the gas station....which is daily since i drive 25-30K miles per year

 

I tried many times to "feel" the difference in power from 87 to 91 and could not. I also never saw any difference in mpg. 91 might get you a small fraction of a second faster on the drag strip, but it seems like a waste of money for daily driving.

 

Contrary to common belief, the ECU does NOT tweak the timing according to the fuel you use, it only has 2 timing maps, a standard map and a knock map. When the knock sensor detects knocking, it switches to the knock map, which results in decresed performance and incresed fuel consumption.
Both maps are fixed, so when it is running on the standard map, it is running the same timing regardless of what fuel you use (provided it is not knocking).
So if you don't get knocking on 87, then you probably aren't going to see much differences in economy or power by switching to 91 or 93.
the only 'self learning' the ECU does is fuel trim.