91 or 94 octane gas.

[D Bergstrom]

For the first 1,800 miles of owning my 2020 GT, I only ran 87. For the next 800 miles, I ran 91. (Highest we can get around here.) I bought the Ford Performance calibration and wanted to run a few tanks of 91 through the system to get ready to install the calibration. Car is strictly driven on the street, no track use. Noticed absolutely no difference in the way the car performed or fuel mileage after switching to 91. After the calibration, I definitely noticed a difference. That being said, if I didn’t install the calibration, I would still be running 87 for the majority of the year, would only run 91 for the few months of summer due to heat.

To the OP, try a few tanks of 94. If you notice a difference in performance and you are ok with the extra cost, run the 94. If not, run 91.

Doug

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[ice445]

Hello; We both may be wrong. I have episodes of ENGINE MASTERS saved and decided to watch one of them. Season 6 Episode 2 Does Octane Make Power?
They used the same engine with 87 & 91 pump gas, plus some 110 av gas and some 116 fuel.

The results
87 octane = 498.9 lb/feet torque(T) @ 5200 RPM / 539.4 HP @ 6400 RPM/ AV T 475.5 AV HP 452.7
91 octane = 501.1 lb/feet torque(T) @ 5300 RPM / 539.6 HP @ 6400 RPM/ AV T 476.3 AV HP 453.6
110 octane = 499.1 lb/feet torque(T) @ 5300 RPM / 539.9 HP @ 6400 RPM/ AV T 475.1 AV HP 452.5
116 octane = 497.4 lb/feet torque(T) @ 5300 RPM / 541.3 HP @ 6400 RPM/ AV T 474.7 AV HP 452.1
A one and a half HP spread. Not much

They did an E85 set of runs
E 85 = 506.5 lb/feet torque(T) @ 5200 RPM / 551.5 HP @ 6400 RPM/ AV T 484.0 AV HP 460.9
8.8 HP difference.

The dyno runs were at cool temps without a load on the engine

Hack seems to have it nailed. I had an 1989 F-150 with two tanks. I ran 87 in one and 91 in the other. With a load it might ping so I switched to 91. Ordinary driving I ran it on 87.

I saw that episode but it's not a valid comparison to our cars which have adaptive knock sensing. Our cars will keep adding timing until the knock line is found or it hits something called mbt (which is basically where you won't make any more power). It will make a lot more power and torque on 94 vs 87 octane because of this. Now whether you will notice or not depends entirely how you drive and the ambient conditions.

Old engines with carbs or simple ecu's dont care as much about octane.

 

[K4fxd]

I think up to 95 octane for the stock logic.

Some say 94. None of the pump gas will get me stock MBT timing in my area.

OP try the 94 and if it feels better and or you get a bit more mileage........

 

[GL95]

Hello; We both may be wrong. I have episodes of ENGINE MASTERS saved and decided to watch one of them. Season 6 Episode 2 Does Octane Make Power?
They used the same engine with 87 & 91 pump gas, plus some 110 av gas and some 116 fuel.

The results
87 octane = 498.9 lb/feet torque(T) @ 5200 RPM / 539.4 HP @ 6400 RPM/ AV T 475.5 AV HP 452.7
91 octane = 501.1 lb/feet torque(T) @ 5300 RPM / 539.6 HP @ 6400 RPM/ AV T 476.3 AV HP 453.6
110 octane = 499.1 lb/feet torque(T) @ 5300 RPM / 539.9 HP @ 6400 RPM/ AV T 475.1 AV HP 452.5
116 octane = 497.4 lb/feet torque(T) @ 5300 RPM / 541.3 HP @ 6400 RPM/ AV T 474.7 AV HP 452.1
A one and a half HP spread. Not much

They did an E85 set of runs
E 85 = 506.5 lb/feet torque(T) @ 5200 RPM / 551.5 HP @ 6400 RPM/ AV T 484.0 AV HP 460.9
8.8 HP difference.

The dyno runs were at cool temps without a load on the engine

Hack seems to have it nailed. I had an 1989 F-150 with two tanks. I ran 87 in one and 91 in the other. With a load it might ping so I switched to 91. Ordinary driving I ran it on 87.

Not a coyote and doesn't have active knock sensing...

 

[Buldawg76]

The dyno runs were at cool temps without a load on the engine

All dynos put a load on the engine whether it's a chassis or engine dyno either by means of a weighted fluid filled drums in a chassis dyno or by means of fluid or electrical generator resistance on an engine dyno. Thats why when you see them go WOT throttle and you hear the engine rpm loaded down it is from the resistive load being applied before the engine starts to increase in rpm to whatever redline they take it up to.

BD

 

[S550HPP]

In my experience the higher the octane the better the milage s it's pretty much a wash cost wise. I use 94 all the time from a dedicated pump hose so it feels special haha.

I notice a difference between 91 and 94. Seems like throttle response is razor edge with 94 and gets duller the lower the octane.

In winter with 94 and HPP turbo the car rips.

 

[Paris MkVI]

From the 2015 owner's manual:

2.3L EcoBoost and 5.0L V8 Engines​

We recommend regular unleaded gasoline with a pump (R+M)/2 octane rating of 87. Some stations offer fuels posted as regular with an octane rating below 87, particularly in high altitude areas. We do not recommend fuels with an octane rating below 87.​

To provide improved performance, we recommend premium fuel for severe duty usage, such as trailer tow.​

That said,, I fill up with 93 all the time. THe "seat of the pants" difference is worth it to me. It is there, without question. I have had Mustangs for the simple joy of driving.

JMHO. You do you.

 

[Hack]

In my experience the higher the octane the better the milage s it's pretty much a wash cost wise. I use 94 all the time from a dedicated pump hose so it feels special haha.

I notice a difference between 91 and 94. Seems like throttle response is razor edge with 94 and gets duller the lower the octane.

In winter with 94 and HPP turbo the car rips.

I believe the difference may be more noticeable in a turbo vehicle. Cold days were fun in my FiST as well. Especially -20 or so when it wanted to spin a tire almost any time.

 

[Hack]

Hello; We both may be wrong. I have episodes of ENGINE MASTERS saved and decided to watch one of them. Season 6 Episode 2 Does Octane Make Power?
They used the same engine with 87 & 91 pump gas, plus some 110 av gas and some 116 fuel.

The results
87 octane = 498.9 lb/feet torque(T) @ 5200 RPM / 539.4 HP @ 6400 RPM/ AV T 475.5 AV HP 452.7
91 octane = 501.1 lb/feet torque(T) @ 5300 RPM / 539.6 HP @ 6400 RPM/ AV T 476.3 AV HP 453.6
110 octane = 499.1 lb/feet torque(T) @ 5300 RPM / 539.9 HP @ 6400 RPM/ AV T 475.1 AV HP 452.5
116 octane = 497.4 lb/feet torque(T) @ 5300 RPM / 541.3 HP @ 6400 RPM/ AV T 474.7 AV HP 452.1
A one and a half HP spread. Not much

They did an E85 set of runs
E 85 = 506.5 lb/feet torque(T) @ 5200 RPM / 551.5 HP @ 6400 RPM/ AV T 484.0 AV HP 460.9
8.8 HP difference.

The dyno runs were at cool temps without a load on the engine

Hack seems to have it nailed. I had an 1989 F-150 with two tanks. I ran 87 in one and 91 in the other. With a load it might ping so I switched to 91. Ordinary driving I ran it on 87.

As others mentioned in this thread, the Coyote does more to take advantage of octane than most engines do.

Having said that, what you are talking about is correct to a degree for the Coyote as well. There's only so much power difference between min and max adjustability, especially if ambient temperatures are relatively low. And on the street 99% of the time is spent at partial throttle.

Even at full throttle, it's not like you are going to get 20 HP or something. It's a small amount. Even when I run higher octane on track, I still firmly believe it's partially placebo. I don't for a minute believe I'm protecting the engine from damage. The ECU does that.

 

[sk47]

I saw that episode but it's not a valid comparison to our cars which have adaptive knock sensing. Our cars will keep adding timing until the knock line is found or it hits something called mbt (which is basically where you won't make any more power).

Hello; My understanding from the video is they adjusted timing and other parameters over several runs until they get the better numbers. Not clear if such compares to adaptive knock sensing directly. My take is they did adjust timing to the point of not making any more power.
They did state they were not going to let the engine have "knock" to prevent damage.

Also, pretty sure the engine did not have variable valve timing which might make a difference.

I have 104 episodes saved and have watched 100 so far. A thing that comes out of the setups is the results can be somewhat specific to an engine configuration and may not apply to a different configuration. This was a larger displacement LS type engine making over 500HP on the dyno. It would be better to use a Coyote to get results more specific to the OP's question.

 

[sk47]

All dynos put a load on the engine whether it's a chassis or engine dyno either by means of a weighted fluid filled drums in a chassis dyno or by means of fluid or electrical generator resistance on an engine dyno.

Hello; Yes, you are correct about the way a dyno puts a load on a tested engine. Poor communication on my part. My take is by "load" they meant not pulling a trailer or running hard up a grade in hot weather. They did not want to hurt the engine and were running in a cool dyno building with the only "load" coming from the dyno to get measurements.

 

[ice445]

Hello; My understanding from the video is they adjusted timing and other parameters over several runs until they get the better numbers. Not clear if such compares to adaptive knock sensing directly. My take is they did adjust timing to the point of not making any more power.
They did state they were not going to let the engine have "knock" to prevent damage.

Also, pretty sure the engine did not have variable valve timing which might make a difference.

I have 104 episodes saved and have watched 100 so far. A thing that comes out of the setups is the results can be somewhat specific to an engine configuration and may not apply to a different configuration. This was a larger displacement LS type engine making over 500HP on the dyno. It would be better to use a Coyote to get results more specific to the OP's question.

Compression ratio in some ways is more important than timing when it comes to this issue. The gen 3 coyote for example uses direct injection as a crutch of sorts to allow 87 octane to work at all in the first place since it's 12:1 compression. Thus the engine is always knock limited and trying to figure out the safest way around that. Higher octanes allow the ECU to relax a little bit and push the envelope more, which is why these engines pick up more power than most. Another one I can think of that's similar is the GR86 flat four, although that one requires 91 octane minimum.

With that said I suppose when I said "a lot of power and torque", it's not entirely realistic. It's more just low end torque you lose when the engine runs into knock limitations. 10-20hp isn't a big deal when you can make up to 460, but 20ft/lbs in the low end of the RPM range is more noticeable and will show on a quarter mile slip or dragy run. Of course all depends on ambient temperatures too. If it's 58F outside there's a lot more margin inside the combustion chamber to play with.

 

[sk47]

Even at full throttle, it's not like you are going to get 20 HP or something. It's a small amount. Even when I run higher octane on track, I still firmly believe it's partially placebo. I don't for a minute believe I'm protecting the engine from damage. The ECU does that.

Hello; Interesting take. I figure higher octane fuels at least make it easier for the ECU to adjust without working at extremes.

Back to the OP's question. Guess there are still some questions and opinions. The test engine from the Engine Masters was likely a decent base to answer a basic question about octane and HP.

 

[engineermike]

FYI some ecoboost controls actually float the boost up and down with learned octane so it will make an even bigger difference on those.

 

[sk47]

Compression ratio in some ways is more important than timing when it comes to this issue. The gen 3 coyote for example uses direct injection as a crutch of sorts to allow 87 octane to work at all in the first place since it's 12:1 compression.

Hello; Very good point and my take as well. A carbureted engine with a 12 to 1 compression would, I think, have to be limited to higher octane rated fuels. Direct injection coupled with knock sensors allows to run on 87 octane.

Let me risk showing some ignorance. Gasoline and diesel fuels can both be compressed to the point of compression combustion. That is the way a diesel engine gets combustion, by compressing the fuel+ air mix to something like a 20-1 ratio (not absolutely sure of the ratio).

When gasses are compressed they get hot. Try this if you have a 20 gallon tank shop air compressor. Touch the tank before turning it on after it has sat overnight. Turn it on and then touch it when it builds up a full compression and shuts off. The tank will be very warm to hot. The idea is the air in a large room at say 70 degrees F and 15 PSI is squeezed down to the size of a 20 gallon compressor tank at 120 PSI. The air in that room at 70 degrees has a lot of heat energy. That same amount of heat energy also becomes compressed when forced into the small space of the tank. My bigger tanked compressor gets even hotter as it builds up to 150 PSI.

Diesel fuel must be of a higher-octane rating than gasoline since it requires more compression to self-ignite. But when it does ignite the fact it was compressed much more gets more efficiency out of the fuel. A diesel was always something like 15% to 20% more efficient than a gas engine. My take is because of the compression difference. Direct injection has, in part, made gasoline engines closer to a diesel in terms of energy efficiency.

In a gasoline engine the trick is to compress the air -fuel mix a lot without getting compression ignition. As in a diesel the more the air-fuel mix is squeezed then the more energy can be had. Problem with gasoline is when compressions started getting above 8 or 9 to one there could be ways the air fuel mix can either self-ignite or be ignited by a carbon hot spot for example. (knock)
(more possible ignorance on my part) I think petroleum engineers found a way to arrange the hydrocarbon atoms in crude oil into an eight sided molecule and called it octane. I think they found it resisted self-ignition better than the molecules first used as fuel. The more of these octane rings in the fuels the better it resists compression ignition.

Enough from me for now.

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