87 octane vs 93 octane - ECOBOOST

[Graygoose2021]

I’m pretty sure that’s spot on.

However, I’m really not trying to bait him: I’m genuinely too stupid (but still really curious) to ascertain whether he thinks the physical evidence presented is just lies- or if he just doesn’t approve of the science.

are you saying, Follow the science?

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[wayfarer556]

I'm just a dumb IT monkey, but I know this:
Engine has computer that detects octane
Computer say higher octane make engine run faster
Me put in higher octane
Engine run faster
Smart people say higher octane prevents engine knock
Broke monkey me think short term investment yield long term gain (engine not going explody)
Me spend extra $10 at pump to prevent $10k at dealership morgue
@Ford Motor Company no send me useless forum ping about how sorry they are that me engine explode

 

[Gros Ventre]

Article from Hemmings: "In summary, most modern vehicles do not require higher octane fuels, unless specifically expressed in your owner's manual (read carefully, because there is a difference between higher octane being "recommended" and "required" in the manual)." The key here is whether the manual says required or not. Ford does not use the word "required."

 

[SALEEN961]

The PCM constantly monitors the knock sensors on the 3.5EB and calculates an octane adjust ratio (OAR) in the range of -1 to +1 in an effort to optimize spark advance based on knock sensor activity. We can view the OAR value to determine if increased octane has the potential to offer additional performance. If the octane adjust ratio is already at -1.0, increased octane will provide no benefits. If the OAR is only at -0.5 or worse yet +1.0, increased octane will result in increased power production.

Increased spark advance increases cylinder pressures and torque/hp production. When running 87oct on my truck, it is not uncommon to see -4° of spark advance after the OAR settles in, and when running 93oct it is not uncommon to see +6° of spark advance. You can absolutely feel the difference that an extra 10° of spark advance makes, even with the conservative stock calibration.

 

[Tosh]

I can feel a difference between 87 and 91 when towing. I get about 10-15% better MPG with 91 octane. I decided to run 91 all the time, and I get "clean gas" (Ethanol free) as often as possible.

 

[Graygoose2021]

The PCM constantly monitors the knock sensors on the 3.5EB and calculates an octane adjust ratio (OAR) in the range of -1 to +1 in an effort to optimize spark advance based on knock sensor activity. We can view the OAR value to determine if increased octane has the potential to offer additional performance. If the octane adjust ratio is already at -1.0, increased octane will provide no benefits. If the OAR is only at -0.5 or worse yet +1.0, increased octane will result in increased power production.

Increased spark advance increases cylinder pressures and torque/hp production. When running 87oct on my truck, it is not uncommon to see -4° of spark advance after the OAR settles in, and when running 93oct it is not uncommon to see +6° of spark advance. You can absolutely feel the difference that an extra 10° of spark advance makes, even with the conservative stock calibration.

 

[Chili]

The F-150 3.5 EcoBoost power output is not certified per the SAE J1349 Standard, but the Expeditions is. The Expedition base 3.5 Eco is 380 horsepower/470 lb ft per the J1349 Standard and utilized premium fuel to do so per the website. The same footnote is made on the Platinums 400 horsepower/480 lb ft version. Since the F-150 is even more torque I’d say it’s safe to say that’s on premium even though that torque is not certified per the SAE standard. The F-150 5.0L V8 says right on the website that is it certified per the J1349 Standard on premium fuel, so that 400 HP/410 lb ft is certainly on premium fuel. Nowhere in my owners manual for my 5.0L does it say 87 makes full power. It says 91 or higher is recommended for best overall performance.

Look up dyno results on both the 5.0 and 3.5 on 87 octane. Both made 330 rwhp on Livernois pre-tune runs with regular unleaded. Both made 350-360 rwhp on premium stock. Sorry bro. Premium is called for on both motors for full power. Both are running serious cylinder pressure (12:1 static compression on 5.0 and upwards of 15 psi available boost on the 3.5) detonation resistance helps these motors a lot. You’re just cheap.

I'm sure it's weather dependent. When I ran my 13.6 @100 it was cold and I was using midgrade. Premium probably isn't needed in that case and the truck was even pulling boost back to around 16. If I wanted to maintain that perfromance as much as possible, premium would likely be needed in the summer. Especially last week when it was over 100 degrees!

It just isn't realistic to think you're going to get max power when it's hot on cheap gas with a turbo engine that has high compression. It will drive just fine, but you're not getting as much power.

 

[Chili]

The PCM constantly monitors the knock sensors on the 3.5EB and calculates an octane adjust ratio (OAR) in the range of -1 to +1 in an effort to optimize spark advance based on knock sensor activity. We can view the OAR value to determine if increased octane has the potential to offer additional performance. If the octane adjust ratio is already at -1.0, increased octane will provide no benefits. If the OAR is only at -0.5 or worse yet +1.0, increased octane will result in increased power production.

Increased spark advance increases cylinder pressures and torque/hp production. When running 87oct on my truck, it is not uncommon to see -4° of spark advance after the OAR settles in, and when running 93oct it is not uncommon to see +6° of spark advance. You can absolutely feel the difference that an extra 10° of spark advance makes, even with the conservative stock calibration.

Great info. Some might even call it factual evidence that leans into proof...

Some. But not all will

 

[Chili]

The F-150 3.5 EcoBoost power output is not certified per the SAE J1349 Standard, but the Expeditions is. The Expedition base 3.5 Eco is 380 horsepower/470 lb ft per the J1349 Standard and utilized premium fuel to do so per the website. The same footnote is made on the Platinums 400 horsepower/480 lb ft version. Since the F-150 is even more torque I’d say it’s safe to say that’s on premium even though that torque is not certified per the SAE standard. The F-150 5.0L V8 says right on the website that is it certified per the J1349 Standard on premium fuel, so that 400 HP/410 lb ft is certainly on premium fuel. Nowhere in my owners manual for my 5.0L does it say 87 makes full power. It says 91 or higher is recommended for best overall performance.

Look up dyno results on both the 5.0 and 3.5 on 87 octane. Both made 330 rwhp on Livernois pre-tune runs with regular unleaded. Both made 350-360 rwhp on premium stock. Sorry bro. Premium is called for on both motors for full power. Both are running serious cylinder pressure (12:1 static compression on 5.0 and upwards of 15 psi available boost on the 3.5) detonation resistance helps these motors a lot. You’re just cheap.

The F150 3.5 was updated in 2021, was the Expedition too? My findings show that starting in 21 the 3.5's all use the larger turbo's that used to be H.O. only (Raptor/Limited). Usually they don't put the updated engine in until occasionally a refresh, usually a new model. The Mustang for example isn't getting the new 5.0 until 2024, but the F150 got it in 2021.

Could the Expedition is using a higher output tune on the older engine? I've seen 360-370 WHP on a 3.5 F150 and that's not translating to 400hp. More in the 430-440 range.

 

[Snakebitten]

Starting in 2018, Ford quietly upgraded the Turbos on the non Raptor to the same as Raptor.

So technically, only 2017 model F150 "Gen2 3.5 Ecoboost" got different size turbos than Raptor.

However, the HO 3.5 Ecoboost motor does have some internal differences. Nothing substantial, but arguably intended to support a different "tune".

But it's THAT tune that gives it the additional specs more than anything else. And we all know that there's substantial power left on the table for both versions of the motor. Ford decides on the degree of separation. It's marketing that determines the calibration, in my opinion.

 

[Gros Ventre]

The PCM constantly monitors the knock sensors on the 3.5EB and calculates an octane adjust ratio (OAR) in the range of -1 to +1 in an effort to optimize spark advance based on knock sensor activity. We can view the OAR value to determine if increased octane has the potential to offer additional performance. If the octane adjust ratio is already at -1.0, increased octane will provide no benefits. If the OAR is only at -0.5 or worse yet +1.0, increased octane will result in increased power production.

Increased spark advance increases cylinder pressures and torque/hp production. When running 87oct on my truck, it is not uncommon to see -4° of spark advance after the OAR settles in, and when running 93oct it is not uncommon to see +6° of spark advance. You can absolutely feel the difference that an extra 10° of spark advance makes, even with the conservative stock calibration.

Have you figured out what the design point of the engine is? Are those adjustments simply bringing the engine up to its design point? For example the homework I've done revealed that different formulations of gasoline, even with the same octane rating, have different flame propagation rates. This in turn will cause the engine management system to move around the ignition point, much as you've described. So, the question then is: does moving the ignition point for different flame propagation rates mean the peak cylinder pressure is higher or lower? Or does that adjustment mean that about the same peak is achieved. I remain unimpressed with the butt dyno method. Essentially your assertion of increased cylinder pressures means that effectively you have altered compression ratio. That cannot be true. Remember, the purpose of spark advance is to achieve complete burning of the fuel charge by a certain point on the curve of the piston motion.

 

[Gros Ventre]

Also, it's important to recall that the chemistry of the combustion has different target points of power versus economy. See below, the max power point of air to fuel is quite different than that of best economy. Best fuel economy is about 20% leaner than best power. The engine management system is therefore jockeying things around depending on the demand being sensed. Spark advance is different for rich vs lean mixtures.

 

[Gros Ventre]

From the Hemmings article I linked above: "Higher octane gas is processed through additional steps that further refine the blend and cause it to burn more slowly than lower octanes." Thus the computer has to adjust the ignition point farther away from the desired peak cylinder pressure point. So, yeah, the advance is going to be increased... Just because of using higher octane fuel but not because it's producing more power.

 

[Natetroknot]

?

 

[joejamesatou]

No, the difference is that $360/yr pees out the exhaust pipe. There is no statement by Ford that hgher octane increases power output. What likely happened is that Ford so designed the engine, when in its perfect state right off the assembly line floor, that with 87 octane it is right on the edge. Read that link I put up, you'll find that as an engine ages it coud go over the edge on 87 octane, but if you up the numbers it'll still run smoothly. That's all there is. The thermodynamics is clear: octane higher than designed adds nothing to power. The power comes from the area under the curve. The ony way you make that area under the curve larger is by upping the compression ratio and therefore raising the "Brake mean effective pressure" in the engine. Octane just doesn't do this.

Dude. Yes. It was tested exactly like that.
Here:
https://www.caranddriver.com/features/a28565486/honda-cr-v-vs-bmw-m5-ford-f-150-dodge-charger/
Here:

Here:
https://tfltruck.com/2018/12/can-the-2019-ford-ranger-make-300-hp-on-premium-fuel/

20hp, a .6 faster 0-60 and .6mpg better mileage was road tested by C/D. Backed up by TFL and Engineering Explained and countless others. The ECU adds around 1.9 pounds of boost and advances timing to make more power with 93 octane.

It can run just fine on 87. And you're right that adding octane to an engine that higher than designed for doesn't add power. Your link is accurate for naturally aspirated engines.

HOWEVER, it does not apply to forced induction engines that can add more boost and timing. Your article does not apply to an Ecoboost engine. Nowhere in the article does it mention boost pressure. The ECU has knock sensors that will advance boost and timing till it hits knock. Run 93 and you get almost 2 more pounds of boost.

Further, adding an aftermarket tune can add well over 100 horsepower by adding more boost and timing. No need to change compression or displacement.

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