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[RTHolmes]

many ECUs these days do adjust timing depending on the fuel, mine is 10yrs old and does it. iirc they just use the most aggressive timing possible and back it off a little when they detect the onset of knocking. really modern systems do it for each cylinder, for each stroke.

[Golfer]

I have to disagree because of performance and results. The computer predicts based on recent driving habits but I've got a few thousand miles using each type of fuel and a marked increase in performance using 93 compared to 87. Like I said, 1.5-2 mpg and if anything I've raced more with 93 using it almost exclusively the last few thousand miles. One tank full isn't enough and it's the second and subsequent tanks that tell the story.

The car definitely checks the fuel and it certainly appears to reflect in the predictive as well as performance figures. Or it's a statistical anomaly that changes between what button is pressed at the pump.  And can be duplicated.

[CAP1]

I run 93 octane always in my Hemi.  Remember.....the higher octane the better ignition (less chance of knock etc.)
Higher octane doesn't necessarily improve performance if your car is good on 87 octane suggested from the factory.
BTW the Hemi requires at least 92 octane.

However running lower octane then suggested can do a good deal of damage over time.  I think CAP would agree.

Don't be cheap....also....don't expect much better performance running 93 octane over the 87 suggested by your manufacturer.
Minimal if any performance gains will be realized.  Wasted money.

Run the 87 and save some money....to buy new stuff for your car!

 also don't forget.....modern cars will pull timing when they sense knock.......

 according to ford, my gt will produce 400hp on 87. 412 on 93.

[CAP1]

It's a wash in my car with the cost per mile being aroun the same. The car knows what you're feeding it and the extra 1.5-2mpg you gain offsets the cost of the fuel.  I also pick up about 2 tenths and choose the better fuel for consistency. At least until the hottest day I've ever run happened. 

The fuel computer knows it too when I would fill up a second tank of 93 after 87 and back again. Very different mileage numbers and according to Vehicalc better results. YMMV, literally 

 here's another question for ya............what brand gas do you use?

 a friend of mine, and his wife have been experimenting. they've found that if they use sunoco cheap fuel, they gain about 3 to 5 miles per tankful. that's on her saturn vue with the honda v6, and his z4 with a 3.0 straight six. in his case, it could be partly due to driving, as he's been unemployed for a bit, and his foot is getting a bit lighter too. in her case, nothing's changed.
 they're messing with shell right now, to see if the results are the same or not.

[CAP1]

Golfer old friend the car doesn't (computer) know what you put into it for fuel.  It however does know how much air and fuel it is set for (PCM)
The PCM in most modern cars can be recalibrated.  For MOPARS it's a simple matter of pulling Fuse #2 for 30 seconds.  Then starting and
driving like ya stold it    Believe it or not the PCM has a sort of memory on how you drive.  Find out the procedure for your beautiful Mustang.
The only way you'll tell the quality is by how the car runs.  If it says 87 from Ford you should have no problems with predetination, engine knock etc.
If you get better gas mileage it will be minimal.  Same with performance....if any.  One thing I do know is any automoblile tuned correctly will run
better on low humidity days.....usually those days are also cooler.  If however you have two days 80 degrees, the one with the lowest dewpoint
will make your car run better, less water taken into the intake with the air.

 bolded....you know fords have been like this since eec4?

 that said, in a sense, he's right. the modern ecu's will sense burn time, necessary kv to ignite the a/f mixture, etc. they will adjust accordingly.

[Golfer]

Shell V Power or Sunoco 93 for the last ~5000 miles.

V power this weekend.

[CAP1]

Shell V Power or Sunoco 93 for the last ~5000 miles.

V power this weekend.

 THOSE are about the 2 best out there. i think with shell, 95% of what goes into the storage tanks has to be shell....the rest can be whatever. with sunoco(at least when i worked at one back in the late 90's early 2000's) i think the requirement was something like 80% or 85%.

[MrRiplEy[H]]

Shell V Power or Sunoco 93 for the last ~5000 miles.

V power this weekend.

Down here the V-power comes from the same refinery as any regular gas I think it was different for a few months, now only difference is probably additives and the price.

Gas additives can make a huge difference. Back in 90's they introduced a gas called 'terra'. It had extremely good washing properties so it cleaned up engines pretty good. Some engine models got cleaned so well that valve socket lubrication got washed away too effectively seizing them. There were a few very unhappy customers for it

You can also buy octane increasers to make your gas racing level 100+ octane stuff.

[CAP1]

Down here the V-power comes from the same refinery as any regular gas I think it was different for a few months, now only difference is probably additives and the price.

Gas additives can make a huge difference. Back in 90's they introduced a gas called 'terra'. It had extremely good washing properties so it cleaned up engines pretty good. Some engine models got cleaned so well that valve socket lubrication got washed away too effectively seizing them. There were a few very unhappy customers for it

You can also buy octane increasers to make your gas racing level 100+ octane stuff.

 additives are what makes the difference. around here, most of our gas comes from the same refineries too

[MarineUS]

Two cars that I wish I had the money to fix

[Flench]

Two cars that I wish I had the money to fix

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What is that first car you posted ? It has the same front end as a 72 firebird .

[CAP1]

What is that first car you posted ? It has the same front end as a 72 firebird .

 it's looking like a pontiac ventura to me.

[Flench]

it's looking like a pontiac ventura to me.

I have never seen one . I had a 72 firebird at one time and it had that same front end on it . So it must be a 72 model ?

[Xasthur]

Already run 93.

Why do Americans get lower octane fuels than other countries?

91 is the lowest we (in Australia) have, 95 is average and 98 is considered 'premium'.

[RTHolmes]

its a different scale.