What Octane are you using for the 5.0?

[Khyber]

mine certainly doesn't knock and bang and ping with 87 in it. Although It's only had gas put in it twice.

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[Qwkynuf]

... The stock tune is for 91 and above, run less or even worse run less and run it hard and you're rolling the dice for the long term longevity of your motor.

Simply. Not. True.

The owner's manual *clearly* states that the recommended fuel is 87 octane for all 3 engines. For the Ecoboost and 5.0, they "recommend premium fuel for severe duty usage, such as trailer tow", for "improved perfomance" in those situations. Trailer towing typically involves more low rpm/high throttle input situations than normal driving, which increases the likelihood of "lugging" the engine.

Surely, Ford knows their engines well enough to be able to determine whether they should be requiring regular or premium fuel. They required premium on the GT500, they required it on the Lightning, heck, they even required it way back in the SuperCoupe. It seems logical to infer that since they *don't* mention premium as a requirement for the 2015 Mustang... It probably isn't required.

And here is a little secret - premium fuel does *not* contain any more energy than regular. It is not "more powerful" than regular. It is formulated with a higher octane to heptane ratio which makes it more resistant to spontaneous combustion. Compression ratio (including *effective* compression ratio, due to forced induction) has an almost direct linear relationship to octane requirement.

From http://science.howstuffworks.com/gasoline:

It turns out that heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot and nothing happens. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.​

The converse of that is that if your compression ratio isn't high enough to need the higher octane, you are not likely to benefit from it. In modern engines, ignition timing is advanced pretty significantly - especially as compared to the the old "points and condenser" cars of my youth. The idea is to fire the spark plug *before* the piston arrives at top dead center on its compression stroke. This is done for several reasons:

• because the flame front takes time to propagate within the combustion chamber
• compressing the fuel charge into the burgeoning flame front increases homogeneousness of the mixture, improving combustion efficiency
• starting the burn prior to TDC allows the combustion to be timed so that maximum combustion pressure is achieved exactly at, or just slightly after TDC

A problem can arise when you advance timing too far. If the flame front is ignited too far before TDC, then the expanding gasses increase the effective compression ratio as the piston rises on its compression stroke. If this effective compression ratio exceeds the fuel mixture's threshold to spontaneously combust, then the fuel ignites too early. This can spike pressures in the combustion chamber as the piston attempts to compress the expanding gasses from the combustion. This is known as "detonation", and it is bad (if allowed to continue).

The engine control systems on modern cars control ignition timing and monitor for detonation thousands of times per second. They are constantly adjusting ignition timing right to the verge of detonation and then backing it off slightly. If the factory tune is not programmed to ever advance timing beyond the detonation threshold for regular fuel, then it will never benefit from higher octane. In fact, it would likely make less power and return worse gas mileage with premium.

Also note that combustion pressures and detonation thresholds (and therefore, maximum timing advance) are not static values. Air density, temperature, humidity, and engine load all contribute.

At the end of the day, run what you want. Just make sure that you run what you want to run for the right reason.

 

[Free Agent]

mine certainly doesn't knock and bang and ping with 87 in it. Although It's only had gas put in it twice.

You wouldn't know if your car was knocking/detonating more than likely unless you are monitoring the knock sensor data or watching timing being pulled as knock retard. Data logging reveals the truth.

On top of that, this time of year you aren't going to notice it as much. See what happens in August at 95 degrees and a 70 degree dew point. It is noticeable then.

Most people aren't ever going to notice or even care. Just don't be surprised when we nip you at the light cause we're running 93. ;)

 

[Todd15Fastback]

Burned 93 octane in my 2011 Maxima. Burned 93 in all my V8 Mustangs. My '15 will be tuned for 93 and will run that. My dealer filled up the car with 93.

 

[Khyber]

You wouldn't know if your car was knocking/detonating more than likely unless you are monitoring the knock sensor data or watching timing being pulled as knock retard. Data logging reveals the truth.

On top of that, this time of year you aren't going to notice it as much. See what happens in August at 95 degrees and a 70 degree dew point. It is noticeable then.

Most people aren't ever going to notice or even care. Just don't be surprised when we nip you at the light cause we're running 93. ;)

well i don't race sooo... :headbonk: ...but if the damn thing blows up with 87 in it, guess who's fixing it??? :ford:

 

[michformulas]

I fill up with 93. It would just bother me that I am not getting full performance even though I know I wouldn't even notice. Sick....I know. Scratches, daily driving in the salt/snow, car washes. None of that bothers me but the motor needs to be babied in my world.

 

[Khyber]

bottom line is if more than 87 was needed, it would be in your manual. you'll be just fine with 87... 91 and 93 isn't some mystical formula. If someone wants to run 87, then fine... if someone wants to run 93, then fine. It's all got ethanol in it anyways.

 

[kn7671]

Its not just the horsepower,though I guarantee you all this 1 percent stuff is nonsense because I can always sense a tangible difference immediately using 92 over 87. But regardless 87 is just garbage gas, its not as good for your engine regardless. I mean I can tell every single time how it runs rougher, feels worse. It feels like its adding stress. I wouldnt use 87 ever for that reason alone.

This is just wrong, though I'm not condoning running 87-octane fuel in an engine setup and tuned for 93-octane fuel.

Lower octane fuel is not "garbage gas", and in many cases is exactly the same fuel with a few extra chemicals added to increase the octane.

Lower octane gas ignites easier, and at higher compression ratio's you either have to lower the Air/Fuel Ratio which increases bad emissions, or retard the ignition timing.

If you are one of those that run 87-octane to save $30 to $100 per month on fuel, and you are experiencing weird driveability issues, I suggest trying 87-octane from different gas stations to validate consistency, and switch brands if resolved.

 

[achenator]

SO much BS in this thread. The recommended fuel for the 5.0 is 87. The owners manual does not say "minimum". As for pulling timing at different temperatures, do you think Ford didn't test this thing like crazy at different temperature extremes before recommending 87?

 

[Budwise]

It doesnt matter how you guys want to interpret the manual, if you run 87 your car will be constantly having to adjust due to knock/ping. You may not ever hear it but that is because the copperhead ECU is pretty badass and is saving your butt by constantly dialing down the timing parameters. If you doubt it feel free to get a SCT Tuner yourself and do the data log and enjoy seeing 18 degrees of timing instead of 25 and watch your knock retard spike like a mofo during WOT runs or engine load. I don't play the ignorance is bliss card with my car, but thats me. I'm not guessing or blowing smoke.

 

[Asharus]

i'd love to see these logs

 

[texag70]

Got almost 1200 miles and it's been 93 only. Now paying 2.23 a gallon at our local Sam's Club. Reg. is 1.90.

 

[Khyber]

This thread...

 

[Wolfman625]

93 always

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