gas octane question for PB F150

[dolsen]

I guess my buddy gros venture blocked me after replying to my posts. That’s not very conducive to a productive debate ?‍

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[Suns_PSD]

There are some misleading posts in this thread.

As others already pointed out, there is static compression which is just a measurement of the cylinder volume ratio of BDC/ TDC; and then there is dynamic compression which is functional compression which is altered through the use of variable cam timing and changes all of the time in response to many factors, fuel octane being one of them. This means your motor absolutely can have higher real-world compression as a result of the ECU making adjustments. Edited: To add further clarification, when the valves are open, compression is lost, when they are closed compression is gained. So, altering the timing of the opening/ closing of the valves absolutely changes the real-world compression.

I'm not familiar with all of the changes that Ford makes to compensate for low octane fuel but we know for a fact that ignition timing is altered as well as air/ fuel ratios and these changes absolutely effect horsepower and efficiency.

Practically speaking I've tested both 87 Octane and 93 Octane on a stock Powerboost and what I saw and felt was notably better acceleration (10% better acceleration with high octane has been proven by others) and a 1 mpg improvement, under the same (mild) driving conditions when I switched the high octane and the ECU was given a tank to adjust parameters.

To be clear: 93 Octane cost around 15% more $, for around a 5% increase in mpg. Which means from a cost per mile standpoint, it's a total looser.

I'm 99.9999% certain you'd be totally fine running 87 Octane in your daily driver F150, with no damage or problems.

Would I head across a West Texas Summer on I-10 pulling a travel trailer up those long grades on 87 Octane? Hell no. I think that is flirting with piston holed disaster. And apparently Ford thinks so as well.

I choose to run 93 Octane full time because the engine pulls up to highway speed smoother, and I like that. Since I already had that expense built it, it made sense for me to add a Livernois tune since I already was running the expensive fuel. NO RAGRATS!

 

[rpold150]

I'm old school when it comes to engines so I don't know much about variable cam timing. But getting back to Gros' premise is that if an engine (including all mechanical and electronic components) is designed to work optimally with 87 octane, does the engine actually take advantage of higher than needed octane. As stated, modern engines retard timing and make other adjustments based on engine feedback like detecting knock thus running with sub-optimal performance.

What is not clear to me is if the F150 engines will take advantage of more octane than necessary. If the engine does not detect knock or any other negative feedback, will it continue to advance ignition timing beyond the optimal designed profile? If not, then adding 110 octane race gas will not give you any more power than using the highest octane that will produce zero knock. I assume there are maximums to spark advance and A/F ratios that won't keep increasing just because there is additional octane.

I think it gets back to the question of are the F150 engines designed to work best with 87 octane or 91. If they are optimized for 91 and they are always adjusting down to work with 87, then yes it makes sense that using 91 octane will result in better performance. But if they are designed for 87 and don't see any negative feedback, then using higher than necessary octane won't produce more than what was optimally designed.

Adding in all the other factors like air intake temp, altitude, carbon buildup, load, etc., will also help determine the optimum octane.

Just my old school .02.

 

[dolsen]

I'm old school when it comes to engines so I don't know much about variable cam timing. But getting back to Gros' premise is that if an engine (including all mechanical and electronic components) is designed to work optimally with 87 octane, does the engine actually take advantage of higher than needed octane. As stated, modern engines retard timing and make other adjustments based on engine feedback like detecting knock thus running with sub-optimal performance.

What is not clear to me is if the F150 engines will take advantage of more octane than necessary. If the engine does not detect knock or any other negative feedback, will it continue to advance ignition timing beyond the optimal designed profile? If not, then adding 110 octane race gas will not give you any more power than using the highest octane that will produce zero knock. I assume there are maximums to spark advance and A/F ratios that won't keep increasing just because there is additional octane.

I think it gets back to the question of are the F150 engines designed to work best with 87 octane or 91. If they are optimized for 91 and they are always adjusting down to work with 87, then yes it makes sense that using 91 octane will result in better performance. But if they are designed for 87 and don't see any negative feedback, then using higher than necessary octane won't produce more than what was optimally designed.

Adding in all the other factors like air intake temp, altitude, carbon buildup, load, etc., will also help determine the optimum octane.

Just my old school .02.

Sounds to me like you’re asking all the right questions and have the correct idea

 

[Suns_PSD]

I'm old school when it comes to engines so I don't know much about variable cam timing. But getting back to Gros' premise is that if an engine (including all mechanical and electronic components) is designed to work optimally with 87 octane, does the engine actually take advantage of higher than needed octane. As stated, modern engines retard timing and make other adjustments based on engine feedback like detecting knock thus running with sub-optimal performance.

What is not clear to me is if the F150 engines will take advantage of more octane than necessary. If the engine does not detect knock or any other negative feedback, will it continue to advance ignition timing beyond the optimal designed profile? If not, then adding 110 octane race gas will not give you any more power than using the highest octane that will produce zero knock. I assume there are maximums to spark advance and A/F ratios that won't keep increasing just because there is additional octane.

I think it gets back to the question of are the F150 engines designed to work best with 87 octane or 91. If they are optimized for 91 and they are always adjusting down to work with 87, then yes it makes sense that using 91 octane will result in better performance. But if they are designed for 87 and don't see any negative feedback, then using higher than necessary octane won't produce more than what was optimally designed.

Adding in all the other factors like air intake temp, altitude, carbon buildup, load, etc., will also help determine the optimum octane.

Just my old school .02.

You are asking the correct questions, and Ford has answered them pertaining to the '21 PB (likely applies to all PBs) making it pretty clear that the engine is optimized around 91 Octane. Which makes perfect sense because the EPA mpg rating test uses high octane fuel, and every manufacturer needs to do well on that test for CAFE reasons.

(Copied from EricR's post) An excerpt from the 2021 user manual:

"Some fuel stations, particularly those in high altitude areas, offer fuels posted as regular unleaded gasoline with an octane rating below 87. The use of these fuels could result in engine damage that will not be covered by the vehicle Warranty.

For best overall vehicle and engine performance, premium fuel with an octane rating of 91 or higher is recommended. "

What is particularly interesting to me is that Ford doesn't even want you running low Octane fuel at altitude. They didn't state that it's totally fine due to slower burn rates at altitude. This is likely due to their ability to use the turbos to cram the same number of O2 molecules into the engine, therefore still needing the same quality of fuel that they require at low altitudes.

The way I read the above is that the engine is fine at 87 Octane, as this is within the range the ECU can compensate for. But it's never appropriate to run sub 87 Octane.

And that for best performance run 91 or higher. Which acknowledges that your PB can make adjustments with higher Octane fuel and run better.

 

[nomarhits400]

I guess my buddy gros venture blocked me after replying to my posts. That’s not very conducive to a productive debate ?‍

It wasn't a "you" problem brother- don't sweat it too much....

 

[Suns_PSD]

Another note: It's pretty well documented that having just enough Octane typically results in the best economy. To be clear I mean just enough for the current timing/ etc.

So, this will typically result in (for example) 91 Octane getting better mpg (and power) than say 95 Octane in an engine that is set up for 91 Octane.

In that vein, I'd love to see someone test mid-grade economy vs. hi-grade economy.

Snakebitten, you have tracked PIDs in the PB and been able to watch timing and I assume other factors change with higher Octane fuel. So here is my question: Is the change linear? For example, do you get the exact same changes going from say 87 to 89 octane, as you do going from 89 to 91 octane? Or instead does the amount of (for example) timing advance decreases as you reach higher octane numbers?

For example, might you get 75% of the mpg and power gains running mid-grade, for only half the cost?

 

[Gros Ventre]

I've given the above slings and arrows some thought. There are two competing issues intertwined: Engine efficiency versus engine power output. The engine is designed for a certain raw full power output. That is not influenced by the various things like computer spark control or variable cam timing etc. That is determined by the compression ratio, breathabilty, displacement, and supercharging (eg turbocharging in this case). The other elements of computer controls, variable cam timing, detonation detection, etc, all serve to improve the efficiency of the engine (eg MPG). The key here is the engine does not produce more "power", rather it sips fuel more miserly at partial power levels as those EPA folks are wanting. So, one might ask, if the engine is more efficient doesn't that mean it can produce more power? Answer: No. that's because the power rating is determined by the full power design of the engine. In other words it can only produce that full power level its designed for (displacement, volumetric efficiency, supercharging, and compression ratio). For a given set of design parameters as above the power output will go up as compression ratio goes up (along with required octane rating). A gasoline engine (eg spark ignition) could be designed with a compression ratio comparable to diesel engines. It would actually produce more power, more efficiently than a comparable diesel engine.... however, the fuels industry could not produce a cost effective fuel that could meet the required octane for such an engine. Separate these two competing issues in your mind. Also note that with gasoline direct injection much of the issue of detonation is sidestepped. If the gasoline isn't in the cylinder during the compression stroke, it can't detonate. I'm aware of the small amount of gasoline input by the intake manifold injectors. I infer that Ford has balanced the fuel input between manifold injectors and GDI to minimize detonation.

 

[nomarhits400]

I've given the above slings and arrows some thought. There are two competing issues intertwined: Engine efficiency versus engine power output. The engine is designed for a certain raw full power output. That is not influenced by the various things like computer spark control or variable cam timing etc. That is determined by the compression ratio, breathabilty, displacement, and supercharging (eg turbocharging in this case). The other elements of computer controls, variable cam timing, detonation detection, etc, all serve to improve the efficiency of the engine (eg MPG). The key here is the engine does not produce more "power", rather it sips fuel more miserly at partial power levels as those EPA folks are wanting. So, one might ask, if the engine is more efficient doesn't that mean it can produce more power? Answer: No. that's because the power rating is determined by the full power design of the engine. In other words it can only produce that full power level its designed for (displacement, volumetric efficiency, supercharging, and compression ratio). For a given set of design parameters as above the power output will go up as compression ratio goes up (along with required octane rating). A gasoline engine (eg spark ignition) could be designed with a compression ratio comparable to diesel engines. It would actually produce more power, more efficiently than a comparable diesel engine.... however, the fuels industry could not produce a cost effective fuel that could meet the required octane for such an engine. Separate these two competing issues in your mind. Also note that with gasoline direct injection much of the issue of detonation is sidestepped. If the gasoline isn't in the cylinder during the compression stroke, it can't detonate. I'm aware of the small amount of gasoline input by the intake manifold injectors. I infer that Ford has balanced the fuel input between manifold injectors and GDI to minimize detonation.

I mean, the power increase using higher octane has been documented several places on the Ecoboost engine in the F150, right?:

“Power at the wheels dropped from 380 to 360 horsepower with the change from 93 to 87 octane”

https://www.caranddriver.com/features/a28565486/honda-cr-v-vs-bmw-m5-ford-f-150-dodge-charger/

 

[JExpedition07]

I grow tired of this conversation. All of the engines in the F-150 lineup are designed to run best on premium 91 octane. Let me drop that bomb. That is what grade fuel these engines are designed to run on.

Ford states this right on their website. Power ratings are done on premium, and the manual states premium supplies the best performance. How is my 5.0 rated at 415 horsepower /420 lb ft on E-85 If it cannot take advatage of higher octane?? Magic?!? Is there a little magic elf under my hood that waves his wand when I fill it with 105 octane Ethanol? Your argument makes zero sense. These motors do make more power on premium. End of story. The engine is designed to run on minimum 87 octane, that’s not giving you top performance on any turbocharged or high compression engine. That is simply within design parameters to avoid spark knock.

 

[dolsen]

I grow tired of this conversation. You are a bad listener. All of the engines in the F-150 lineup are designed to run at max performance on premium 91 octane. Let me drop that bomb. That is what grade fuel these engines are designed to run on.

Ford states this right on their website. Power ratings are done on premium, and the manual states premium supplies the best performance. How is my 5.0 rated at 415 horsepower /420 lb ft on E-85 If it cannot take advatage of higher octane?? Magic?!?!? Is there a little elf under my hood that waves his wand when I fill it with Ethanol? Your argument makes zero sense. These motors do make more power on premium. End of story. The engine is designed to run on minus 87, that’s not giving you top performance on any turbocharged or high compression engine.

Lol looks like ol what’s his face is still at it. He clearly doesn’t understand what he’s saying, he did me a favor by blocking me so I cannot see his posts

 

[Gros Ventre]

Yes, what the above says is that the engine is designed for at least 91 Octane. Given the computer control capability of the engine they derate it electronically to enable use of lower octane (I believe this to be a "Sales" pitch). Thus my point about the design features of compression ratio (10.5:1), breathability, supercharging, spark controls. Note that Gasoline Direct Injection enables finer control of detonation since there is very little gasoline in the cylinder during the compression stroke.

 

[Snakebitten]

What is not clear to me is if the F150 engines will take advantage of more octane than necessary. If the engine does not detect knock or any other negative feedback, will it continue to advance ignition timing beyond the optimal designed profile? If not, then adding 110 octane race gas will not give you any more power than using the highest octane that will produce zero knock. I assume there are maximums to spark advance and A/F ratios that won't keep increasing just because there is additional octane.





Just my old school .02.

The 3.5 Ecoboost uses what I have seen described as multiple timing tables. Which table currently chosen as the base table for the PCM to use is determined by various sensors, but the KR (knock) sensor is most influencial. It can cause the PCM to switch to a more conservative or more aggressive timing table in a fairly brief amount of time if it's values meet certain thresholds.

Another PID that you can monitor to get an idea of whether the timing table in use is conservative or aggressive is called OAR. If you are monitoring your KR PID, and you see it at either end of the spectrum for a length of time or frequency, you will see the OAR value adjust. If the OAR value adjusts, that's synonymous with the timing tables in play.

And you can also monitor the timing advance PID and clearly see it reflect the relationship between OAR and KR.

But you brought up another good point. The factory strategy (tune) has its limits too. Once OAR reaches a value that selects the most aggressive timing table available in the strategy, no amount of octane increase would increase could lead to a timing table that doesn't exist.

On the 3.5 Ecoboost, OAR pegs at -1
Less than -1, like say -.67 would be leaving potential timing advance on the table. And again, you can see that reflected in the timing advance PID.

The screenshot below is one 93 octane. Because of the "quietness" of the knock sensors (-3) the OAR is pegged at -1. And you can see that the truck is currently running 26° of advance.

But this is all at 0 load because the truck is in Park. It's just a screenshot.
I have a million of them. ?

Only 93 or better will get OAR to -1, thus the timing table that allows the pcm to advance the timing at the highest levels in the factory strategy

If you arrive at the gas station and pump 87 or 91 into the tank in sufficient quantity, you will literally witness the KR go positive because the current timing table is too aggressive. A few minutes later the OAR will make its first drop in value, which immediately switches timing tables and you will see that reflected as well. If KR stays +positive (knock detected), the sequence continues until harmony is found in the combustion chamber.

It's a fascinating torque management engine management system. All of which I have oversimplified dramatically.
(because I only barely grasp it)

 

[rpold150]

Only 93 or better will get OAR to -1, thus the timing table that allows the pcm to advance the timing at the highest levels in the factory strategy

This is a rather interesting data point.

I did some lunchtime reading on the MX+ PIDs and your dashboards. I have the MX+, but have never done anything with the dashboards. I'm ready to go set them up so I can monitor KR, spark timing, and OAR, amongst others.

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