Octane Adjustment Ratio - Ecoboost

[MNgopher]

I've been monitoring the "Octane Adjustment Ratio" (OAR) in my 2016 F150 with the 2.7l Ecoboost using a variety of Premium fuels using Torque on my phone.

For those who are unaware, the 2.7 Ecoboost requires 87 octane fuel, but the owners manual suggests the following:

For vehicles with EcoBoost engines, to provide improved performance, we recommend premium fuel for severe duty
usage such as trailer tow.

It appears they've built something into the logic for the engine controls to take advantage of the higher octane gasoline, and the OAR appears to be where its acknowledged.

In any event, after many tanks of gas, I've found some tremendous variation in the OAR depending on brand. So far, I've logged the following (from best to worst - negative is better in this case): (Note all are Top Tier Fuels)

Shell Premium 91 E10: -0.8
Superamerica Premium 91 E10: -0.7
Holiday Premium 91 E10: -0.5
Kwik Trip Premium 91 E0 (non-oxy): -0.2

The OAR changes within about 10 miles of filling up (I generally wait to fill until the low fuel light turns on). It may adjust another tenth after driving significantly farther, but the change occurs rather quickly.

Most surprised at the variation in the ratio, all on premium 91 octane fuels. The non-oxy delivered better fuel mileage (as expected), but it appears it does not unlock better performance at the same time.

Also find this interesting in light of the "Fuel is Fuel" ideas constantly put forth. Under that logic, all sources should all result in the same performance. With some knowledge of the fuel supply here, there are 5 distinct sources that can be identified (with three brands directly tied to the source), along with mixed supplied from the Magellan pipeline system available. Have said it before, but the reality is you need to figure out what the local supply situation is before assuming all the fuel is the same since it all comes from the same terminal (there are multiple terminals here - all with different sources).

 

[horse123]

Buying a turbo car and running it without at least 91 is stupid. I know some are designed to be fine with 87... but they still gain SIGNIFICANT horsepower with premium.

 

[MNgopher]

If the engine is designed to run on 87 octane, why is it stupid to run it? If it costs more to run on premium and has adequate power on regular, what is the problem?

I have not found any scientific testing (admitting I have not looked hard) that show the HP and torque difference on this engine when running regular and premium. Plenty when tunes are added and run, but not on stock tuning.

Again, was more surprised to find such variation in the fuel - particularly when so many live by the "fuel is fuel" idea... Does it make a difference? No idea, but there certainly is a noticeable difference to the logic running the engine...

 

[Johnny2Bad]

Many engines will modify the performance parameters based on the apparent octane of the fuel. Your Owners' Manual should tell you what Octane fuel you should be running and whether there would be a performance penalty or benefit from adjusting up or down. It's true that with a standard performance non-computer controlled motor it's a waste, but the modern mill changes that.

I'm not surprised to see Shell Premium offered good performance. It's not obvious or even evident in every motor I own and use, but I and my buddies all notice a difference with the motorcycle if we don't fill with Shell. There are differences in the additive package with Top Tier fuels ... many brands use Techron purchased at Wholesale from Chevron but Shell uses their own additive formula and as far as I know don't sell it to others.

 

[09_GXP]

Interesting findings between the different types of fuel. I've also watched my OAR number change with the different fuels. I can't recall all the exact numbers but did get close to -1.0 with some left over 100 octane race fuel. It definitely, adds a good bit of tip in response when unloaded.

Originally Posted By: horse123
Buying a turbo car and running it without at least 91 is stupid. I know some are designed to be fine with 87... but they still gain SIGNIFICANT horsepower with premium.


Strongly disagree with this statement. In towing situations I see at least 10% better fuel economy with 93 octane over 87 octane. However, that does not outweigh the higher cost. Any performance difference is really had to determine since the truck has more than enough power on 87 octane. In special circumstances, such as towing long hills, it may make a difference but as an overall blanket statement if the engine was designed and tuned on 87, then 87 is more than sufficient.

 

[shanneba]

Does it change more if you do a full throttle run? It looks like it varies from -1 to +1 from what I have seen on the interwebs.
Have you also monitored knock count for each cylinder (how many times the particular cylinder knocked) and knock intensity for each cylinder?

What happens if you add a bottle of Red Line SI1 fuel system cleaner to the Shell VP?

 

[wemay]

I have done this as well, with the Santa Fe Turbo. We've noticed no difference. Hyundai also claims HP gains with this engine but in other models. We typically fill from 1/2 tank, alternating grades as we go.

 

[Hokiefyd]

Originally Posted By: MNgopher
It appears they've built something into the logic for the engine controls to take advantage of the higher octane gasoline, and the OAR appears to be where its acknowledged.


I think many engine management control strategies have this same type of logic. And I think it's not a whole lot more complicated than "continuously adjust the timing so that it's as advanced as it can be for the fuel currently being injected so as to not damage the engine". Ford apparently uses the OAR as a user-readable indicator of this (good on them for making this available to the user!), but I think most ECUs use this type of (non-disclosed) strategy.

It appears that Ford has a baseline adjustment of "0" (probably relative to a baseline spark advance map). If the timing has to be retarded from this baseline if using a lower octane fuel, then it makes an adjustment reported as a positive OAR. If the timing can be advanced from this baseline if using a higher octane fuel, then it makes an adjustment reported as a negative OAR. These numbers reported are likely very buffered, as the state of timing advance is being continually adjusted as you drive down the road. In fact, I'll bet it's some sort of a moving average of the last X minutes' or miles' of duration. The computer likely makes the actual adjustment much sooner than the computer reports it.

To those who have tracked OAR on their EcoBoost Fords, what are the numbers after running a tank or two of regular fuel?

I've noted before that I can see a clear difference in spark advance in my naturally-aspirated Honda Ridgeline when running premium fuel. The increase in performance and response is great enough that I always use premium in it, even though Honda recommends it for towing situations only (similar to Ford's recommendation). I think this type of language in the owner's manual is more or less direct evidence that the engine CAN make use of the extra octane at all times, and that, while 87 octane is "fine", best performance is achieved with higher octane, regardless of whether or not you actually have a trailer hitched to the truck. Whether or not one actually chooses to use higher octane is, of course, a personal choice.

 

[MNgopher]

I have not monitored OAR on 87 octane regular, but plan to give it a go.

I don't doubt that others have made a similar strategy in their engine management systems. I think its great there is something to actually monitor and acknowledge that is what is happening though! FWIW, I tried similar comparisons in my old F150 and came to the conclusion that running anything other than regular 87 octane was a waste of money as there was no noticeable changes in any parameter that I could find - at least using decent quality 87 octane gasoline.

I have not noticed an immediate change after a full throttle run - it seems like it changes after about 10 miles after a nearly full tank refill.

I know of one source reasonably local with non-oxy 93 octane. It is expensive through! May go with a little bit to try it out on a nearly empty tank. So far though, Shell seems to be the go to on this parameter. Too bad, as they are not super common (as compared to the others in this area) and tend to be a bit on the dumpy side of things... (FWIW, many of the major National brands just are not here in this market - BP has significantly declined, Marathon is down to a small number, and Citgo, Phillips 66, and Conoco are gone. There are some Mobil stations around, but not a lot...)

 

[440Magnum]

Originally Posted By: MNgopher
. The non-oxy delivered better fuel mileage (as expected), but it appears it does not unlock better performance at the same time.


Absolutely no surprise there. Non-oxygenated fuels have a higher energy density, so miles/gallon is generally better.

Alcohol is a tremendously effective octane booster, so although it has low energy density requiring more to be injected on each cylinder firing, it delivers more power because the engine can set the timing with less regard for detonation. The most extreme example is a flex-fuel vehicle like my Ram. Mileage drops like a rock on E-85 (from ~16 in regular commuting to roughly 12 under the same conditions), but power and throttle response are both better because E85 is far higher octane than even E0 premium.

 

[Nate1979]

I recall people monitoring for knock events. Can you do this (or is this the same thing)?

 

[Kawiguy454]

Originally Posted By: 440Magnum
Originally Posted By: MNgopher
. The non-oxy delivered better fuel mileage (as expected), but it appears it does not unlock better performance at the same time.


Absolutely no surprise there. Non-oxygenated fuels have a higher energy density, so miles/gallon is generally better.

Alcohol is a tremendously effective octane booster, so although it has low energy density requiring more to be injected on each cylinder firing, it delivers more power because the engine can set the timing with less regard for detonation. The most extreme example is a flex-fuel vehicle like my Ram. Mileage drops like a rock on E-85 (from ~16 in regular commuting to roughly 12 under the same conditions), but power and throttle response are both better because E85 is far higher octane than even E0 premium.



I think your idea of why alcohol makes more power is incorrect. 91 alcohol blend and 91 pure gas have the same octane/knock resistance so the ECU will use the same timing control settings. The reason alcohol makes more power especially on turbo applications is due to its cooling effect on incoming air charge as it is atomized.

 

[Kawiguy454]

I have no reservations about running regular 87 in a vehicle that can adjust to it. A vehicle that makes 500hp on premium is of no use doing 65 down the highway under only aero load. If you're racing or towing or just have a huge need to overcompensate for other areas premium is just a waste.

 

[horse123]

Originally Posted By: 09_GXP
Interesting findings between the different types of fuel. I've also watched my OAR number change with the different fuels. I can't recall all the exact numbers but did get close to -1.0 with some left over 100 octane race fuel. It definitely, adds a good bit of tip in response when unloaded.

Originally Posted By: horse123
Buying a turbo car and running it without at least 91 is stupid. I know some are designed to be fine with 87... but they still gain SIGNIFICANT horsepower with premium.


Strongly disagree with this statement. In towing situations I see at least 10% better fuel economy with 93 octane over 87 octane. However, that does not outweigh the higher cost. Any performance difference is really had to determine since the truck has more than enough power on 87 octane. In special circumstances, such as towing long hills, it may make a difference but as an overall blanket statement if the engine was designed and tuned on 87, then 87 is more than sufficient.


If the only thing you care about in a car is getting the most out of your gas money then buy a prius old man, not a turbo.


If a turbo car is tuned to run 87 there's basically no point in having a turbo, unless your compression ratio is like 1:2. You could easily make over 100 more hp with a tune on a car that's meant to handle 87 with a turbo, obviously you're going to need to tune for at least 91 though. Turbo tuned to run low octane = majorly down on power compared to its (reliable, safe) potential.

Pointless. Turbos should not be seen as a primarily efficiency increasing device... they're a performance enhancing device.

 

[MNgopher]

I'm sorry - the last post has me chuckling.

For reference, the 2.7 TT Ecoboost in the F150 puts out 325 hp and 375 ft-lbs of torque on 87 octane gas... The 3V 5.4 in my 2004 F150 put out 300 hp and 365 ft-lbs of torque. And the power delivery is so much nicer on the Ecoboost...

Guess some people need to get over their pre-conceptions about what a Turbo can do...

 

[Kawiguy454]

Originally Posted By: horse123
Originally Posted By: 09_GXP
Interesting findings between the different types of fuel. I've also watched my OAR number change with the different fuels. I can't recall all the exact numbers but did get close to -1.0 with some left over 100 octane race fuel. It definitely, adds a good bit of tip in response when unloaded.

Originally Posted By: horse123
Buying a turbo car and running it without at least 91 is stupid. I know some are designed to be fine with 87... but they still gain SIGNIFICANT horsepower with premium.


Strongly disagree with this statement. In towing situations I see at least 10% better fuel economy with 93 octane over 87 octane. However, that does not outweigh the higher cost. Any performance difference is really had to determine since the truck has more than enough power on 87 octane. In special circumstances, such as towing long hills, it may make a difference but as an overall blanket statement if the engine was designed and tuned on 87, then 87 is more than sufficient.


If the only thing you care about in a car is getting the most out of your gas money then buy a prius old man, not a turbo.


If a turbo car is tuned to run 87 there's basically no point in having a turbo, unless your compression ratio is like 1:2. You could easily make over 100 more hp with a tune on a car that's meant to handle 87 with a turbo, obviously you're going to need to tune for at least 91 though. Turbo tuned to run low octane = majorly down on power compared to its (reliable, safe) potential.

Pointless. Turbos should not be seen as a primarily efficiency increasing device... they're a performance enhancing device.


Horse, With respect I think you miss the forest for the trees... The origins of a turbo were exactly to produce power when you need it. And to be economical when you don't. Using your logic going driving anywhere would be a WFO drag race. Reality is probably 95% cruising in traffic where economy does matter.

Not sure where you live but the price difference around here is 87/$2.00 91/$2.50 a gal so around ~20% more. so to get 10% more performance costs %20 more money. The question then becomes why do you need to waste 10% of your fuel cost of you're not racing or towing? and there is no argument to be made seriously that its safer or more reliable. The only thing stupid is wasting money on gas you don't need to.

 

[MNgopher]

The discussion on the non-alc vs alcohol containing fuels is interesting.

I understand that the OAR is not a direct reading of octane, but a measure of engine performance based on knock resistance (ie: advancing the timing up to the point it starts to knock and then backing off a bit, and then as was pointed out doing a longer term average to provide buffering).

Under that logic, shouldn't all things being equal octane wise, regardless of the alcohol content, the OAR should be the same? For whatever reason, the one brand on non-oxy I tried (due to availability and being top tier - I've got two other sources of non-oxy that are not top tier I can explore) delivered a significantly lower number.

I expected the fuel economy rise on the non-oxy fuel (simple energy density). Again, surprised at the OAR being so much lower than other 91 octane fuels.

I have not directly monitored knock events. Will have to figure out if I can and get it programmed in.

 

[horse123]

Thanks for proving my point. Mercedes makes 375hp and 350lb-ft on a 2 liter because they're not being complete morons and putting a turbo on to increase efficiency by 1 or 2 mpg. They're actually using it for what it should be used for.

 

[BobFout]

Many in this thread are unaware how DI allows the use of RUG with turbo'd and higher compression ratio petrol engines...

 

[09_GXP]

Originally Posted By: horse123
Thanks for proving my point. Mercedes makes 375hp and 350lb-ft on a 2 liter because they're not being complete morons and putting a turbo on to increase efficiency by 1 or 2 mpg. They're actually using it for what it should be used for.

The key word in your statement is efficiency. You can either make more power for the same fuel or make the same power with less fuel. Depending on the application you can choose which path to go down. When I'm cruising to work using 40hp on the interstate, it doesn't matter if I have 60 or 600 hp in reserve.