91 or 94 octane gas.

[bobdes368]

Is it worth the extra dollar plus to put 94 octane in my 5.0 GT?
I drive the local roads, and occasionally on highways.

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[junits15]

It makes a difference, it’s up to you to decide if you can feel it enough to be worth the extra money.

 

[sk47]

Hello; One reason I continue to consider a Mustang GT is that it is OK to run 87 octane fuel. (at least the last time I checked this was so) The gas octane ratings around my area are 87-89-91, with 91 being the common highest offered.
The cost of 91 over 87 is 70 cents per gallon lately. That is $7 dollars more for each ten gallons purchased.

I must assume 94 octane will be an even bigger price differential. But I get the question. Folks i have talked to about it tell me running 87 might drop the HP some. How much is the big question. Something like 12 HP is one answer I recall but suspect this is a guesstimate. A GT has over 400HP. Not sure I would notice losing 12 HP just driving around.
You appear to be asking the other way. Can 94 octane get HP over 91 octane. I do not think so, at least with a factory tune and stock equipment. I have known several folks who own vehicles designed to use 87 octane but do use 91 octane. The take is they are wasting money buying the higher octane fuel. The engine cannot take advantage of the extra octane ceiling.

A gallon of 87 octane fuel has the same energy density as a gallon of 91 octane. The higher octane allows the timing and/or compression to be altered to eek out a bit more power before preignition (detonation/knock) occurs. Some benefit in terms of compression when using direct injection (DI). Modern DI engines tend to run higher compression if my take is correct.

Took a while but my take is 91 will be enough.

 

[Garfy]

When I tested my car at sea level using 87 vs. 93 octane, there was a noticeable difference in the 0-60 test with 87 taking 6.0 seconds and the 93 resulted in 4.9 seconds. Of course, this is a 6 point octane difference, whereas you're looking at only 3 points, but still I imagine that 3 points will be noticeable. That being said, it depends on the cost difference. Where I live we only have 85 regular and 91 premium so I always use the 91, and difference is about 30 cents per gallon (I have no choice as the manual specifies 87 as the minimum).

 

[GregO]

Is it worth the extra dollar plus to put 94 octane in my 5.0 GT?
I drive the local roads, and occasionally on highways.

I use Costco Premium. I justify premium because of the MPG gain vs regular. I do think the premium fuel adds a bit of a performance gain IMO.

 

[HKusp]

I use Costco Premium. I justify premium because of the MPG gain vs regular. I do think the premium fuel adds a bit of a performance gain IMO.

It absolutely does. The PCM is constantly monitoring parameters and adjusting timing based off of them. If it senses knock because of lower knock threshold that 87 provides versus 91-94, it pulls timing which costs you HP.

 

[Ramairetransam]

on a stock mustang nope , they were tuned to run on 91 so 94 wont help .

 

[Paddles]

I thought the knock was the limiting factor, won't the computer make use of every bit of extra octane even into the 100s?

 

[Cheatham]

The highest octane available preferably 93

 

[WildHorse]

I used 94 religiously for the first 4 years of my car ownership right up until Husky Energy was sold to CO-OP. Then it was reduced to 91. Sigh...

I thought the knock was the limiting factor, won't the computer make use of every bit of extra octane even into the 100s?

I think up to 95 octane for the stock logic.

 

[sk47]

on a stock mustang nope , they were tuned to run on 91 so 94 wont help

I thought the knock was the limiting factor, won't the computer make use of every bit of extra octane even into the 100s?

I think up to 95 octane for the stock logic.

Hello; The question of will the higher octane (94 in this discussion) yield more performance (HP)(Torque) or perhaps fuel economy is a good one. I do not know the exact answer so can only guess.

My take is an engine designed to run on 87 octane gains little if any benefit from running higher octane fuels. There are physical parameters in play that cannot be changed. Lower actual compression ratio may be among the major reasons. That physical ratio is set and a tweaking by a computer which advances or retards ignition timing cannot change the set mechanical ratio in terms of actual compression.
I get that on a Coyote V8 the actual compression ratio is, I think, mechanically (physically) set a bit higher than a commuter sedan. This allows the pistons to squeeze the air+fuel mix a bit tighter providing the fuel is treated so as to prevent pre-ignition (knock)(detonation).
I understand the cams themselves also can be mechanically adjusted with oil pressure and this may also help prevent detonation.
The trick in modern engines is that a set of computers can adjust the timing and cam position on the fly. In the old days we had a set of spring-loaded weights inside the distributer that could change the timing. Also, a vacuum motor usually mounted outside the distributer hooked into the intake manifold could alter the timing some. These were preset and did not respond to real knock.

Wildhorse may have the answer that 95 is the upper limit.

 

[Hack]

I'd say it's a question only you can answer. When my Mustang was stock, I ran 87 most of the time. I couldn't tell a difference with 91. I felt it was a waste of money to run higher octane on the street. 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.

When it's 40 or 50 in the morning and the high is in the 60s, the octane doesn't do much for you. If it's really hot in New Jersey and you are racing, go with the highest octane you have available. If you are abiding the laws on the street, especially on a cool fall day when the tires aren't going to hook anyway, the high octane won't do anything.

 

[WildHorse]

Wildhorse may have the answer that 95 is the upper limit.

That be according to LUND RACING.

 

[GL95]

Hello; One reason I continue to consider a Mustang GT is that it is OK to run 87 octane fuel. (at least the last time I checked this was so) The gas octane ratings around my area are 87-89-91, with 91 being the common highest offered.
The cost of 91 over 87 is 70 cents per gallon lately. That is $7 dollars more for each ten gallons purchased.

I must assume 94 octane will be an even bigger price differential. But I get the question. Folks i have talked to about it tell me running 87 might drop the HP some. How much is the big question. Something like 12 HP is one answer I recall but suspect this is a guesstimate. A GT has over 400HP. Not sure I would notice losing 12 HP just driving around.
You appear to be asking the other way. Can 94 octane get HP over 91 octane. I do not think so, at least with a factory tune and stock equipment. I have known several folks who own vehicles designed to use 87 octane but do use 91 octane. The take is they are wasting money buying the higher octane fuel. The engine cannot take advantage of the extra octane ceiling.

A gallon of 87 octane fuel has the same energy density as a gallon of 91 octane. The higher octane allows the timing and/or compression to be altered to eek out a bit more power before preignition (detonation/knock) occurs. Some benefit in terms of compression when using direct injection (DI). Modern DI engines tend to run higher compression if my take is correct.

Took a while but my take is 91 will be enough.

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

 

[sk47]

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

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.

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