Power and efficiency difference with lower octane levels?

[RocketGuy3]

Hey folks. I've tried checking the owner's manual for the answer to this question, and tried searching this forum, but I'm struggling to find anything conclusive.

I remember Ford in some TSB or maybe even in the official owner's manual for my previous 2015 S550 GT said that the car would only take about a 1% hit in both gas mileage and power when using "regular" 87 octane instead of the recommended 91 octane. It's been a long time, so I can't remember exactly where I saw it, but I'm confident it was reported by Ford. It was such a small difference that basically whenever I wasn't going to the track, I would happily just get regular gas.

Does anyone know if there is any remotely official number like this for the 5.0 in our Mach 1s (and presumably for Bullitts from this gen)? I know this one uses direct injection and I believe a higher compression ratio, so it probably takes a bigger hit with 87 octane, but I'm curious how much? And/or has anyone dyno'd the car at different octanes?



EDIT: Because of all the preachy replies, I'd like to add a reminder that I am not soliciting your advice. Only information. You can run whatever type of fuel you like in your car, as can I in mine.

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[robvas]

This has been discussed a million times

 

[Rael]

Unhelpful.

 

[robvas]

It's definitely more than 1%

https://www.mustang7g.com/forums/threads/87-octane.164494/

 

[SnowFox]

I have never used below 93 on the Mustang even when the mustang was stock. moto it's fine maybe not ideal. Lots of here about it. But lots of friends and co-workers with Coyote F-150s use whatever gas is cheapest and seem to have no issues.

My bronco on the other hand the power difference is very noticable and very really and annoyed the shit out of me

 

[MAGS1]

Hot take: just because you can doesn’t mean you should.

Why contemplate regular 87 octane? The price difference ends up being $7-$10 per fill up. That’s a couple cups of coffee a week. The manual does state pretty clearly that to get the optimal performance from the engine, to use 91 or higher.

Yes the car will run fine on 87, it was designed to do that. But it was really designed with 91 or 93 as optimal, so why not get optimal performance if you paid optimal performance price for the car? That’s the way I view it anyway

 

[S550HPP]

It's a matter of principal and performance would you eat junk food and fake ice cream or organic unprocessed no seed oils and real ice cream.....

 

[sk47]

Hello; A while back the topic was discussed in a long thread. I went to a saved episode of the TV show ENGINE MASTERS. Here is what I found. Bear in mind the test in the episode was only about the power/torque output in a single test engine. Not an engine such as the Coyote.

• #15

GL95 said:
I would imagine the difference is a lot closer to 50 than 12

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 said:
I did run higher octane on track days and sometimes in the middle of summer when it was supposed to be warm - like over 90 for a high.

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

 

[Joe Gonsalves]

Octane rating is its resistance to preignition. The higher the number the more additive is added. They all start out as the same fuel. The reason the higher octane makes more power is that the engine timing is advanced. With today's knock sensors the PCM monitors the sound of the engine listening for detonation. It will retard the timing until it no longer knocks. Conversely, it will advance timing to just before it knocks. All of course within a set range. When a car is tuned the range of the ignition timing is advanced to run on the higher octane beyond the factory limits. But now you can no longer downgrade the fuel since the knock sensor will not be able to adjust the timing lower than what the tuner has set. Now with some premium fuels, they also add a bunch of other additives to help keep the valves clean. These additives along with the octane booster, displace the amount of fuel you get, so 1 gal of 87 will actually have more BTUs in it than 1 gal of 93. Granted it's a small fraction but worth noting since it will affect gas mileage per tank full. What Engine Masters, great show by the way, sometimes tell you, and sometimes they don't mention, is when they run these tests, Steve Burle` or Steve Dulcicich will tweak the ignition timing and carburetor for optimal performance. They edit out the number of tuning dyno pulls to only show the final result. So the results sk47 listed should have included the number of degrees of timing added to arrive at those power numbers.

 

[Pistol_91]

Diesel is good for fuel mileage. Mix in some diesel to the 87

 

[ShadesOfBloo]

Yes the car will run fine on 87, it was designed to do that. But it was really designed with 91 or 93 as optimal, so why not get optimal performance if you paid optimal performance price for the car? That’s the way I view it anyway

I think I see what you're saying, but I don't need optimal performance for the drive to work.
I chose a V8 over an Ecoboost because it sounded so much better.

When Ford said the Coyote would run on 87 octane, to me the next question was:
Is it made to run on 87 without knocking,
or does Ford mean a sensor will detect the knocking and adjust for it?

The latter would mean that there is still some knocking with 87 octane.

 

[Joe Gonsalves]

I

I think I see what you're saying, but I don't need optimal performance for the drive to work.
I chose a V8 over an Ecoboost because it sounded so much better.

When Ford said the Coyote would run on 87 octane, to me the next question was:
Is it made to run on 87 without knocking,
or does Ford mean a sensor will detect the knocking and adjust for it?

The latter would mean that there is still some knocking with 87 octane.

It will run fine on 87 with the Ford stock tune. Mine before I added the Ford performance kit, ran just fine. The only time you may have an issue is at high elevation. Then you may need to run 91.

 

[robvas]

When Ford said the Coyote would run on 87 octane, to me the next question was:
Is it made to run on 87 without knocking,
or does Ford mean a sensor will detect the knocking and adjust for it?

The latter would mean that there is still some knocking with 87 octane.

It will sense the detonation and then pull timing to compensate

If you put higher octane in, the computer will add some until it senses it again

 

[sk47]

So the results sk47 listed should have included the number of degrees of timing added to arrive at those power numbers.

When Ford said the Coyote would run on 87 octane, to me the next question was:
Is it made to run on 87 without knocking,
or does Ford mean a sensor will detect the knocking and adjust for it?

The latter would mean that there is still some knocking with 87 octane.

The only time you may have an issue is at high elevation. Then you may need to run 91.

Hello; Joe is correct. The guys at Engine Masters often run and tune over several dyno runs. The do mention such in the programs. Sometimes timing is changed. Best i can recall for that particular engine they wound up with the same or similar timing.

Shades asks a good question. In that same thread a member posted some results of knock events in Coyote running on 91 octane if I recall correctly. The point being there can & will be knock under some conditions even with 91 or 93 octane fuel. The Coyote has a somewhat higher compression ratio than engines of past decades. In the past engines without the engine nannies of a Coyote would have to run 91 or higher octane in order to survive. My take is the Engine can detonate with 91 or 93 but the nannies save the day.

Joe is correct i think. High elevations, hot temperatures and high loads can increase preignition (detonation=knock). You do not want to run 87 octane in a Coyote while pulling a trailer thru Death Valley.

The point of my post is the energy which makes HP & torque is the same in a gallon of 87 as in 91, 93, 110 or 116 octane. There are oxygenated fuels have more energy because they have extra oxygen. Same for nitrous.

 

[RocketGuy3]

Hot take: just because you can doesn’t mean you should.

Why contemplate regular 87 octane? The price difference ends up being $7-$10 per fill up. That’s a couple cups of coffee a week. The manual does state pretty clearly that to get the optimal performance from the engine, to use 91 or higher.

Yes the car will run fine on 87, it was designed to do that. But it was really designed with 91 or 93 as optimal, so why not get optimal performance if you paid optimal performance price for the car? That’s the way I view it anyway

I suspected I would get a lot of preachy replies like this. It's not something I plan to do regularly, but as I mentioned in the OP, sometimes to me it's a matter of principle when a station wants to charge 50% more for premium.

Additionally, I'm just curious if these numbers are available.

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.

I'm confused a bit by your wording. Can you tell me what engine are those numbers from?

It's definitely more than 1%

https://www.mustang7g.com/forums/threads/87-octane.164494/

Interesting, that Dyno seems to suggest 19 hp (or less than 5%). Certainly a worthwhile tradeoff at some of the more egregiously priced pumps in my book.

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