New 5.0 87 Octane Vs. 93 - Overall Runs Better On 93?

Discussion in '2005 - 2014 S-197 Mustang -General/Talk-' started by ScottyG00GT, Sep 13, 2013.

  1. OK don't laugh but it has taken me a month and a half and almost 2,000 miles to figure out that premium is the ideal fuel for this car (a literal reading of my owner's manual implies that 87 is recommended, with higher octane for towing and other extreme use).

    So I tanked up with 93 since 91 is not available at my usual gas station. While I am not sure I noticed an 18 hp SOTP difference, I did notice the following:

    - the "flat spot" at low RPMs seems to be less apparent, and may even be gone. With 93, a couple of times so far I unintentionally broke the tires loose on dry pavement when accelerating up through first gear mid-throttle. It didn't seem a lot faster but the power seems to come on slightly earlier and more evenly.

    - the car used to occasionally lurch when cold if I didn't give it a little more throttle, either when backing out of the driveway or starting off in first. Nothing bothersome; I figured I was just getting used to the car. But now with premium fuel, that characteristic seems to be gone for the most part.

    I was curious if anyone else has had this happen, or if I am imagining things? I figure anything is possible with the computer adjusting the air/fuel/timing for octane. BTW I have 3.31s and the car is 100% stock.
  2. Mine is a daily drive so I usually fill up with Sonoco 87, and it runs just fine. However when I do fill up with Ultra 93 at Sonoco the car performs so much better. :)
  3. I've used 91 (highest I can get) since the day I got it. The only time it had anything else was the 87 it was delivered with. I figure $3 a tank (i fill up once every 3 weeks or more) more isn't a big deal to have good fuel in there.
  4. I'll run the higher octane stuff when I'm playing with my timing, but otherwise mine runs just fine on 87 if I keep it around the stock 10-degreee mark. It's just not as snappy.

    That has nothing to do with the fuel and everything to do with the ignition timing.
  5. I usually run 91 in my 5.0. I ran a tank or two of regular through it this last summer for a time, because premium briefly went to as much as 97 cents a gallon higher than regular for some reason. In theory, it makes 10 less horsepower and 13 less torque according to the owner's manual, but that's not enough to notice from driving.
  6. I run only 93.
  7. I seem to recall initial literature for the 5.0 stating that while the engine could be run on 87 octane, maximum HP would be achieved with 91+ octane.

    Running lower octane results in lower hp due to reduced timing
  8. Yeah, I don't know that I can exactly feel the HP. But the car's running characteristics at lower speeds, particularly when pulling away off idle and when accelerating at lower RPM seem to be improved. It doesn't necessarily seem much faster, but it does seem a lot smoother and a bit easier to drive, and I was just wondering if anyone else had this same experience.
  9. I am also noticed my '12 V6 PP runs "smoother" on 91 octane compared to 87
  10. Octane is simply a measure of the resistance to detonation. Simply put: the higher the octane, the harder it is to have premature detonation. Lower octane fuels actually have higher chemical potential energy. Modern ECUs will take advantage of higher octane fuels by advancing timing if there isn't any detonation, thus giving you more power and in turn better gas mileage as the fuel trims are updated.

    That said, if the car permits 87 octane then it'll run just fine with it. 87 isn't substandard or dirty, it's just not as refined. I run 93 because, well, if I can afford a five liter engine then I can put the extra dollar or two it costs per fill-up for high-test.
  11. That's the sticking point here. The Fox Mustang doesn't have a modern ECU. There is no knock sensor, or any other sort of retard or advance feature, so timing remains locked in place regardless of the octane used. Only elevated coolant temperature will tell the ECU to pull timing.

    That's why I can never understand the statement "my car has more power when I fill up with high-test" from the Fox crowd.

    The only way you're going to get more power, is if you physically advance the timing, by moving your distributor. A simple tank of fuel isn't going to do it for you.
  12. Only 93 no matter what for me, I ran lower octanes when I first got my car but 93 seemed a lot better and worth the extra money especially with mustangs
  13. I have been putting 91-93 in for a month now, and I feel like without a doubt it drives more evenly, especially at low speeds. So now I find myself wondering why Ford worded the owner's manual the way they did . . . if it were me writing the text, I'd recommend the 91 for best overall performance but state that it would run on 87. It just seems odd.
  14. 93 is the way to go. I've been using 87 for a little while but my tune runs so much better on 93