Are we really using 87 fuel?

[BlackFerret69]

What is tthe butt dyno performance effect? I am planning on using high octane, since the price difference is minimal to me, but I can undersand if saving a 100 to 200 bucks a year is significant.

https://www.automotivist.com/is-93-octane-worth-it/

I don't use anything but 93 octane in my '06 GT. But it is tuned for it.

One other thing to consider. All things being equal (Mainly driving style), gas mileage usually increases with higher octane fuels.

But that small gain may be mitigated by the heavy right foot, LOL!!

In my case, I average 17-20MPG City, 25-28MPG Highway. That all depends on how many smiles per mile I am having.

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[Jimbo33]

I use 93 octane for a couple of reasons and it is not for performance gains as I do not race it. I am old and I am afraid of using 87 octane in a 12:1 engine. Yes it can do it with minimal losses. Running the engine continuously against the knock sensor which means it has to experience a low level of knock to react to it. I can't imagine that to be good for it long term but I will admit I could be wrong letting past experiences color my thinking. When I consider the cost of the car plus maintenance and insurance, the extra cost of high test is small in the overall picture. I drive a mix of suburban and occasional highway. I have not reset the MPG indicator since I got it. At 11K miles my average has been a little under 22mpg. I am quite happy with that.

 

[GrabThatBlue]

I use 98 instead of 95 because 95 here is E10 and 98 is E5. Ethanol is not that good for the engine, so I run low to non ethanol.

 

[robvas]

Ethanol is not that good for the engine

Why is it not good for your engine?

 

[mmff88gt]

Here is an interesting article from Car and Driver regarding the choice of regular or premium fuel:

https://www.caranddriver.com/features/a28565486/honda-cr-v-vs-bmw-m5-ford-f-150-dodge-charger/

Since my "butt dyno" is not that finely calibrated, I have always used regular in my Mustang after reading this article, except when at high altitudes during a trip out west. I do however try to use "Top Tier" fuel for the additive package. I leave the "Trip 2" on my odometer rolling for long periods to watch gas milege. I currently have over 12,000 miles on the current run and I'm averaging 22.7 mpg with a GT Premium convertible with manual transmission. Your results may vary!

 

[Junkyard Dog]

Here is an interesting article from Car and Driver regarding the choice of regular or premium fuel:

https://www.caranddriver.com/features/a28565486/honda-cr-v-vs-bmw-m5-ford-f-150-dodge-charger/

Imagine 18.5 psi forced induction but only getting a total of 190 hp and 179 lb ft of torque!

 

[Junkyard Dog]

And lol at the BMW making 617 to the wheels on 93 when that is what BMW says is the flywheel number. No wonder those cars can accelerate so quickly.

But, no, they did not risk putting 87 octane in this car. Whew!

You can pick these cars up now with less than 50k miles for about $55k

 

[Racer57]

Octane has no effect or purpose for power, it’s strictly for anti knock.

 

[Junkyard Dog]

The F150 is interesting. So using 87 octane lowers the boost down to 16.2 psi.

Imagine if I said I was going to build an engine for boost and run 87 octane and force 16.2 psi into the cylinder with turbos.

Would you tell me I am crazy?

The F150 pickup did lose add a second and lose 4 mph in the quarter mile, but, still, impressive what modern technology can do with low octane gasoline.

 

[Junkyard Dog]

The Dodge Charger RT in the article is 10.5 to 1.

So I want to ask a question.

What if you use 87 octane in your 12:1 compression Mustang GT religiously and drive it hard even on hot summer days?

I have to think that there must be some sort of longevity issue that will arise at some point before 100,000 miles.

Am I just stuck in the past?

 

[Junkyard Dog]

We did 9 pages on this previously:

https://www.mustang7g.com/forums/threads/does-5-0-coyote-performance-improve-with-octane.170469/

 

[Junkyard Dog]

I could swear I hear the little springs sound of light pinging when at low rpm and adding load, but not enough for the transmission to downshift . . . and this is on 93.

 

[DT-GT]

I actually find decreased gas mileage with higher octane. More power as the computer adjusts for the higher octane, but lower mileage. Oh, plus heavier foot!

I don't use anything but 93 octane in my '06 GT. But it is tuned for it.

One other thing to consider. All things being equal (Mainly driving style), gas mileage usually increases with higher octane fuels.

But that small gain may be mitigated by the heavy right foot, LOL!!

In my case, I average 17-20MPG City, 25-28MPG Highway. That all depends on how many smiles per mile I am having.

 

[DT-GT]

But the computer adjusts timing etc with the higher octane. At that timing without the higher octane it would be knocking big time.

Octane has no effect or purpose for power, it’s strictly for anti knock.

 

[Neggytive]

As soon as the knock sensors determine that the gasoline is sparking off on its own, the computer pulls timing to get it not to knock

Knocking is incredibly bad for any engine, it will beat the snot out of rods and bearings.

Octane is the numerical representation of a fuels resistance to detonation

apples to apples a gallon of "gasoline" has the same BTU / energy content regardless of octane

When you start adding alcohol to it there is a reduction in energy content

E10 gasoline (a blend of 90% petroleum gasoline and 10% ethanol) contains approximately 111,000 to 116,000 BTUs of energy per gallon.

This is slightly lower than 100% pure gasoline, which contains about 114,000 to 125,000 BTUs per gallon, because pure ethanol has a lower energy density (~76,000 BTUs per gallon).

Now that being said, a recalibration for E85 can get you some performace gains, but you have to burn more of it to make it happen. The physics of trying to get uncompressable liquid in larger volumes into the combustion chamber of a high compression engine without inducing rod bending forces is beyond my level of education. All I know is time for max torque, fuel for max HP.

I tend to run ethanol free gas in the 92 or 93 octane rating range in my car since it is widely available in SW Florida where the car is. Where my annual mileage on the car is normally under 2500 miles a year the additional cost over E10 is minimal. Where the car sits for months at a time I like the more stable gas, not only does it not turn to varnish as fast, but any E fuel is hygroscopic, meaning it absorbs water, water that separates out and can cause issues like corrosion.

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