87 octane vs 93 octane - ECOBOOST

[HammaMan]

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.

Even with 87 octane for ~30%+ less in cost, you're still getting double the power we had with the 4.6 liter 2 valves. Granted that was the good old days where at best the 1st number position on gas signs could only display a '1' when warranted. Not sure how much more of this bidenomics we can take. They keep talking about bidenomics like it's a good thing. Maybe there's a live tree somewhere in this dead forest. ?‍

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[SALEEN961]

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.

Running cylinder pressures are impacted by a number of factors such as spark advance, air temperature, camshaft timing, intake manifold pressure, exhaust manifold pressure, and compression ratio, just to name a few. Camshaft timing in particular can cause substantial differences between dynamic compression ratios and static compression ratios.

When an engine cannot safely achieve the maximum brake torque timing on 87 octane, and it has the ability to increase spark advance, using 93oct fuel will allow you to move the ignition point closer to the MBT timing, and it will produce higher cylinder pressures.

The 3.5EB was deigned to run on a minimum of 87 octane, and Ford warns that the use of fuels with less than 87 octane may cause engine damage that will not be covered by the vehicle warranty.

Ford also says that "for best overall vehicle and engine performance, premium fuel with an octane rating of 91 or higher is recommended. The performance gained by using premium fuel is most noticeable in hot weather as well as other conditions, for example when towing a trailer."

I don't know if the 3.5EB in my truck was rated at 400HP and 500 lb.-ft. using 87oct or 91oct, but I do know that Ford says I will gain performance by using 91oct or higher and I understand how critical ignition timing is when trying to maximize power output. When the professionals that designed the engine say to run 91 oct or higher for best performance and all the evidence indicates that running 91oct or higher increases engine performance, there is no reason to doubt them.

 

[joejamesatou]

Hey guys. He has a Plymouth slant six. He totally understands modern engines.

He has his links. The rest of us know so that's that.

 

[HammaMan]

Running cylinder pressures are impacted by a number of factors such as spark advance, air temperature, camshaft timing, intake manifold pressure, exhaust manifold pressure, and compression ratio, just to name a few. Camshaft timing in particular can cause substantial differences between dynamic compression ratios and static compression ratios.

When an engine cannot safely achieve the maximum brake torque timing on 87 octane, and it has the ability to increase spark advance, using 93oct fuel will allow you to move the ignition point closer to the MBT timing, and it will produce higher cylinder pressures.

The 3.5EB was deigned to run on a minimum of 87 octane, and Ford warns that the use of fuels with less than 87 octane may cause engine damage that will not be covered by the vehicle warranty.

Ford also says that "for best overall vehicle and engine performance, premium fuel with an octane rating of 91 or higher is recommended. The performance gained by using premium fuel is most noticeable in hot weather as well as other conditions, for example when towing a trailer."

I don't know if the 3.5EB in my truck was rated at 400HP and 500 lb.-ft. using 87oct or 91oct, but I do know that Ford says I will gain performance by using 91oct or higher and I understand how critical ignition timing is when trying to maximize power output. When the professionals that designed the engine say to run 91 oct or higher for best performance and all the evidence indicates that running 91oct or higher increases engine performance, there is no reason to doubt them.

If you're really worried about every pony, toss you in a small water tank with 2 little sprayers to mist your intercooler with distilled water on WOT to drop your charge air temp.

I've gone back and forth between 93 and 87 and found the only noticeable difference to be a higher price to fill the tank and we're hot and humid here. I can't even WOT in 2wd w/ 87 octane without triggering traction. Granted I do have a 47hp motor with another ~70lbtq making that happen. I only bought the F150 because of the hybrid 3.5 option.

 

[SALEEN961]

If you're really worried about every pony, toss you in a small water tank with 2 little sprayers to mist your intercooler with distilled water on WOT to drop your charge air temp.

I've gone back and forth between 93 and 87 and found the only noticeable difference to be a higher price to fill the tank and we're hot and humid here. I can't even WOT in 2wd w/ 87 octane without triggering traction. Granted I do have a 47hp motor with another ~70lbtq making that happen. I only bought the F150 because of the hybrid 3.5 option.

I already swapped out my factory 195° thermostat for a 180° thermostat, and I've been debating adding a water-to-air intercooler with a refrigerated water tank to my truck. I'm just waiting to see what my IATs look like after I get my truck tuned, right now I hit the speed limiter before my IATs start climbing. I have no issues with traction, but I leave my truck in 4A all the time and I've been really happy with my Continental TerrainContact A/T tires.

When I had my 2014 F150 that was tuned, I went to a bunch of different gas stations in my area and I found that about half of them sold "93oct" that performed on par with or worse than 87oct. Low sales volume and ground water contamination are both issues in my area so I try to stick to newer high volume gas stations near highways. Those stations usually sell 93oct fuel that performs like 93oct fuel.

 

[Gros Ventre]

I end up having to do homework for these posts... that's OK since I learn something each time. But in the end you guys think that the computer controls can override basic thermodynamice, chemistry, & Mechanical Engineering. That's just false. You're spinning fanciful theories that are just wrong. Have a nice day out there, I've had enough trying to teach these fundamentals.

 

[HammaMan]

I leave my truck in 4A all the time and I've been really happy with my Continental TerrainContact A/T tires.

When I had my 2014 F150 that was tuned, I went to a bunch of different gas stations in my area and I found that about half of them sold "93oct" that performed on par with or worse than 87oct. Low sales volume and ground water contamination are both issues in my area so I try to stick to newer high volume gas stations near highways. Those stations usually sell 93oct fuel that performs like 93oct fuel.

Yeah, sucks w/ gas stations that you can't actually see what's coming out of the nozzle. I stick to a 24hr one w/ toptier. They go through a lot of gas so no worry about what's in the tank. How many miles and how's the IWEIs holding up with constant 4a? Since I'm a 22 XLT converted to 4a with IWEIs vs the 'perm locked' variants the 22+ get.

 

[SALEEN961]

Yeah, sucks w/ gas stations that you can't actually see what's coming out of the nozzle. I stick to a 24hr one w/ toptier. They go through a lot of gas so no worry about what's in the tank. How many miles and how's the IWEIs holding up with constant 4a? Since I'm a 22 XLT converted to 4a with IWEIs vs the 'perm locked' variants the 22+ get.

After 2 years I only have 11,000 miles on my truck so I can't really comment on how my constant 4A use impacts the IWEs but I view them as a mechanical fuse that breaks to protect more expensive components and I don't mind replacing them periodically if I have to.

 

[Chili]

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.

I've decided to ignore the wet blanket. Or

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.
[/QUOTE

I end up having to do homework for these posts... that's OK since I learn something each time. But in the end you guys think that the computer controls can override basic thermodynamice, chemistry, & Mechanical Engineering. That's just false. You're spinning fanciful theories that are just wrong. Have a nice day out there, I've had enough trying to teach these fundamentals.

The problem is all your research has been based on trying to prove people wrong and that you're right. Also doesn't take modern ecu variables into play. VVT for example changes cam timing which does in fact change (dynamic) compression ratio.

 

[JExpedition07]

At the end of the day what we all want is for Ford to give us a 5.4L 3V option. I miss the low power, low mpg, and cam phaser/ timing chain issues. Had a nice and lazy 9.8:1 compression. That motor could run 87 all day long (at full power btw) and put glitter in the oil. Those were the days. I think I speak for all of us when I say we would all trade our motors for that package.

 

[Snakebitten]

After 2 years I only have 11,000 miles on my truck so I can't really comment on how my constant 4A use impacts the IWEs but I view them as a mechanical fuse that breaks to protect more expensive components and I don't mind replacing them periodically if I have to.

I love 4A.
Never had an issue with wear on the IWE's in my 2018 & 2021.

My 2022 Powerboost doesn't even have IWE's. Thank you Ford!

 

[Chili]

At the end of the day what we all want is for Ford to give us a 5.4L 3V option. I miss the low power, low mpg, and cam phaser/ timing chain issues. Had a nice and lazy 9.8:1 compression. That motor could run 87 all day long (at full power btw) and put glitter in the oil. Those were the days. I think I speak for all of us when I say we would all trade our motors for that package.

Funny how quickly Ford became the leader in powertrains. It used to be, yeah Fords are ok but the engine kinda sucks and they ride like a dump truck. Things change.

 

[JExpedition07]

Funny how quickly Ford became the leader in powertrains. It used to be, yeah Fords are ok but the engine kinda sucks and they ride like a dump truck. Things change.

What I never understood with the 5.4 was Fords refusal to fix it. All the problems came down to the plastic chain tensioners with the stupid silicon seal and the weak backer plate on the oil pump. Literally just needed to be switched to a cast backer plate and two steel tensioners and they’d have zero oil feed issues. So easy to fix, it’s still crazy to me. They lost a lot of customers over that BS.

 

[SALEEN961]

For anyone who is interested in laboratory testing of the 3.5EB, the U.S. Department of Transportation National Highway Traffic Safety Administration sponsered a bunch of testing on a 2017 F150 3.5EB 10-speed which is very similar to the 2021+ 3.5EB 10-speed F150.

In the laboratory testing conducted by DOE Argonne National laboratory, they specifically investigated the recommendation for using premium fuel when it is not required for the 3.5EB. To quickly summery thier findings I will post a few excerpts from the test report:

The vehicle performance is better for the 93 AKI fuel compared to the 88 AKI fuel. The vehicle accelerates 0.7 seconds faster to 80 mph under maximum acceleration with the 93 AKI fuel. The passing maneuvers are also executed faster with the 93 AKI fuel, except for the 35 mph to 55 mph test. It appears that the powertrain experienced a longer hesitation to build boost and switch gears for the 93 AKI fuel condition on that passing test. The performance tests suggested that the engine torque is increased with the higher octane fuel due to spark advance.

At higher absolute engine loads the spark timing for the 93 AKI fuel is more advanced enabling the engine to operate closer to the maximum brake torque combustion conditions. For the lower octane fuel the spark ignition timing is retarded at these higher loads to prevent engine knocking from occurring.

Laboratory Testing of a 2017 Ford F-150 3.5L V6 EcoBoost With a 10-Speed Transmission

 

[Snakebitten]

Wait!

Did the U.S. Department of Transportation National Highway Traffic Safety Administration state that the 3.5 Ecoboost creates increased torque (work/power) with 93 VS 88?

Nobody will ever believe that.

It's kinda funny that they could have done the same testing 40 years ago (1984) with the SVO Mustang's 2.3 Turbo and came to the same conclusion. Except back then there wasn't the OAR/KR technology so you manually flipped the switch to raise the timing/boost for the 93 fuel.

An Ecoboost ahead of its time?
(Those were adjustable Koni's in those strut towers)

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