Atkinson motor and fuel octane

[DesertSweat]

I want to believe this. The problem is tests keep coming out that say otherwise. Like Car & Driver sticking a dyno on and testing each grade's horsepower:

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

Now, Car & Driver's testers don't even mention ethanol but if that's not the reason, and octane grades do nothing more than avoid knock, then where's the extra horsepower coming from? Or is Car & Driver being paid by the Big10 O&G companies?

We talk a lot about compression ratios in this which is absolutely true, but you can't forget the timing curves based upon load, RPM, IAT, etc, since timing stresses the fuel a lot and impacts efficiency.

All cars will have a base map of timing created using the intended fuel (I think we are fairly confident that the intended fuel for the hybrid is 87) in fairly ideal conditions. Basically it's just a 2 matrix based upon load and RPM. Then there will be tables that generally multiply, or add or subtract based upon certain parameters. Like if you have really high air intake temps or the knock sensor starts getting pre-ignition, or fuel trims are way off, the motor will pull timing.

The more timing the better. But in my experience, I haven't seen maps that increase timing and try to get better efficiency. Because that is tough and requires instrumentation that engines don't come with. (think individual egt and wideband O2 sensors for each exhaust bank). The only real learning I see is in STFT, and LTFT's. Which are fuel trims based upon closed loop operation. ie. the ECU is looking at the MAP of MAF sensor in relation to the wideband O2 sensor and learning how to hit your desired lambda - AFR, because fueling is always a moving target based upon many variables.

TLDR: intended fuel is 87 and the motor would have been tuned using that. You shouldn't see a performance or efficiency increase using a higher octane since all maps are tuned to take away timing.

On the power question, that's a bit more complex, I could speak to the ICE side, but I think there's more potential on the battery motor side. But regardless of either, the ECU needs to be cracked, and software to modify to make any significant gains. But there probably is not enough interest, so there won't be a lot of support.

Because when the created a base timing map they used premium. Anything less results in the knock sensor retarding timing.

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[DesertSweat]

I didn't claim you did say that, but was explaining that the mapping is much more dynamic now thanks to advances in sensors including knock sensors which went from a mere protection device to stop severe damage to a means of calculating its by-the-second operation since they become so very sensitive. The engineers can thus put in maps at extremes, if they choose, that are far too aggressive for average conditions, and use the knock sensor to learn and adjust to more conservative settings as dictated by the specific conditions. Octane aside for example, this can allow them to run mappings that are very lean, leaner than you could expect to run in normal conditions, and just richen as needed.

In any case, as mentioned its overthinking it, as its unlikely to make much of a difference. On a Santa Cruz 2.5T on the other hand that does have 87octane+ as its minimum recommended, it would be interesting to experiment with 93 octane to see if there are aggressive enough maps to take advantage and give you a 15hp or so bump.

There are many tables that impact a timing table. Knock sensor is just one. Knock sensors have gotten better, but the logic is still pretty similar. The goal is to not heavily rely on just the knock sensor because it's riskier. My goal when tuning cars was to have no knock in regular conditions. Which was in tune with what I was seeing from manufacturers. Of course today with tuning they will have trims like with fueling trims that recognize that over time this condition is persisting (using regular instead of premium which the base timing table is created from) and trim timing down a few degrees.

 

[DesertSweat]

I don't know anything about all this science stuff spilled out in this thread. I can ONLY speak from experience I've had with my Toyota/Lexus Hybrid's.

I was using Regular 87 octane in my Toyota Avalon after purchasing the car new back in October 2019. The car is rated at 40-44 MPG. I was getting steady 38 MPG. After around 5 months, the friend, who convinced me to buy the car because he had the same one, said to use Ethanol Free as that was what he was using and was getting around 45-46 MPG. What I found is that a few stations have 93 octane Ethanol Free but MOST are running 89 octane Ethanol Free. And believe me, it does cost more.

I started using the Ethanol Free in the Avalon and found after two tanks of fuel, my MPG shifted to 43-45 MPG and stayed there until I traded it for the Lexus ES300h in May of this year.

In the Lexus, which is basically the same car as the Avalon, the dealer had filled the tank with Regular 87 octane. We let it run down to near empty and filled it with the Ethanol Free 89 octane. Again, I have been getting 43-45 MPG as you can see from the screen shot below from my Fuelly app. Notice for 11 fuel-ups $291.35 / 88 gal = average $3.31 per gallon.

I'll continue to run Ethanol Free 89 octane in the Maverick when I get it and while I can afford it. But since 20 January 2021 it's getting tougher to afford. The only time I will put Regular 87 octane in is when I can't get Ethanol Free when traveling. Luckily I live near the Gulf of Mexico and there is a BIG boating community. So a lot of the stations here offer Regular and Ethanol Free. It's when I travel it becomes harder to find, but there is an app for finding it too.

Are go overall averaging a cheaper price when using ethanol free? There's no disputing you will get slightly more MPG on ethanol free since ethanol is less energy dense.

 

[vap0rtranz]

Because when the created a base timing map they used premium. Anything less results in the knock sensor retarding timing.

Ah. So a better way to explain the effects people notice when leaving pumps is: octane grades don't generate more or less power, and ethanol blends don't affect power produced, but the engine's reaction to lower grade octanes will effectively reduce power output (to avoid knock). Or to borrow one of your words: the engine itself is retarding power.

It sounds to me that we're mincing words over cause & effect. Smarter folks here want to argue that the cause is the engine not the fuel, but the effect is still less power.

 

[JASmith]

I want to believe this. The problem is tests keep coming out that say otherwise. Like Car & Driver sticking a dyno on and testing each grade's horsepower:

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

Now, Car & Driver's testers don't even mention ethanol but if that's not the reason, and octane grades do nothing more than avoid knock, then where's the extra horsepower coming from? Or is Car & Driver being paid by the Big10 O&G companies?

Your quotation doesn't make any sense. You're quoting me on ethanol energy density and linking to an article that doesn't mention ethanol once, so its completely irrelevant. I'm also curious, did you even read that article, or did you just skim the headline?

Summary:
Honda CR-V: 87->93 octane = +8HP
BMW M5: 91->93 octane = +13hp
Ford F-150: 87->93 octane = +20hp
Dodge Charger: 87->93 octane = +14hp

Every single vehicle made more horsepower on higher octane fuels. Idiotically, they also tested the vehicles for peak horsepower under what are generally considered ideal conditions for avoiding knock by being brand spanking new vehicles in cool weather.

If you wanted to see a more significant power delta, they would have tested the M5 on 87 vs 93, and all of the vehicles out on an Arizona summer where its really low humidity and high heat, on vehicles with 20K+ miles on them so there's a little carbon buildup, and dynoed hot engines that have been driving at least moderately hard for a while. That may have made the octane difference on something like a F-150 towing a heavy trailer through Arizona have a +40hp difference.

But even without doing so, they showed as much or more horsepower gain from going even higher than manufacturers recommended octane than you get with popular aftermarket changes like an intake and catback. And I'm not advocating that everyone run higher octane, just that it can only really benefit power wise. When driving cross country in the Mercedes or old Fiat that recommend 91+ octane, we put in 87 octane, because running on cruise control at 70mph for hours and hours is very low strain on the engine that will be running nice and cool with all that airflow and isn't going to knock and you would notice no power difference.

 

[DesertSweat]

I'm learning about NA Atkinson cycle engines like a lot of us, lots of news you can use here.

My paradigm for towing is not really getting more power from higher octane, but maybe helping you keep the power you've normally got if knock conditions occur (more eloquently stated by someone else I found on a google search):

If your engine experiences pre-ignition while towing, it will definitely have more power from higher octane fuel than if the ignition is pulling timing. While the higher octane fuel is not giving it more power directly, if the engine needs it, the higher octane fuel will provide the means for which the engine can maintain the power it should normally have. Pre-ignition can occur due to greater stress on the engine, towing is a prime example of greater stress, especially when doing so up an incline.

So for the Maverick 2.5l is that not true?

Same logic applies. Towing increases stresses usually in the way of more heat through increased load. Hence why the towing package includes things to reject more heat to ambient.

But really you'd want either a logging device or an ability to see real time if you're seeing knock-retard. Or just play it safe and use premium under higher stresses.

 

[vap0rtranz]

I'm also curious, did you even read that article, or did you just skim the headline?

Yes I did read the article. Sad that you think so down on people.

We are all people here. Not bots for you to condescend. Not worth my time.

 

[Peps]

Nope, despite what the EPA test shows, while the 2.0 ecoboost (like all engines) can run on 87 octane, it won't get the advertised power numbers, and will be pulling some timing and richening the fuel mixture at high loads. They don't have to worry about that on the EPA test cycle, because its not a high load test.

Ecoboost 2.0 user manual recommends 91+ octane, if you run less, you will have less peak performance under most conditions.

A page from the new manual made available today... there are reccomandation about high altitude/ towing and ethanol.. for everybody to look at. In my situation, I will be fine with 87 Octane.

 

[DesertSweat]

Ah. So a better way to explain the effects people notice when leaving pumps is: octane grades don't generate more or less power, and ethanol blends don't affect power produced, but the engine's reaction to lower grade octanes will effectively reduce power output (to avoid knock). Or to borrow one of your words: the engine itself is retarding power.

It sounds to me that we're mincing words over cause & effect. Smarter folks here want to argue that the cause is the engine not the fuel, but the effect is still less power.

Pretty much. The modern ECU and the logic is amazing at keeping engines running well while being efficient. Still makes me wonder why some people like their carbs and rotary ignition.

 

[DesertSweat]

Your quotation doesn't make any sense. You're quoting me on ethanol energy density and linking to an article that doesn't mention ethanol once, so its completely irrelevant. I'm also curious, did you even read that article, or did you just skim the headline?

Summary:
Honda CR-V: 87->93 octane = +8HP
BMW M5: 91->93 octane = +13hp
Ford F-150: 87->93 octane = +20hp
Dodge Charger: 87->93 octane = +14hp

Every single vehicle made more horsepower on higher octane fuels. Idiotically, they also tested the vehicles for peak horsepower under what are generally considered ideal conditions for avoiding knock by being brand spanking new vehicles in cool weather.

If you wanted to see a more significant power delta, they would have tested the M5 on 87 vs 93, and all of the vehicles out on an Arizona summer where its really low humidity and high heat, on vehicles with 20K+ miles on them so there's a little carbon buildup, and dynoed hot engines that have been driving at least moderately hard for a while. That may have made the octane difference on something like a F-150 towing a heavy trailer through Arizona have a +40hp difference.

But even without doing so, they showed as much or more horsepower gain from going even higher than manufacturers recommended octane than you get with popular aftermarket changes like an intake and catback. And I'm not advocating that everyone run higher octane, just that it can only really benefit power wise. When driving cross country in the Mercedes or old Fiat that recommend 91+ octane, we put in 87 octane, because running on cruise control at 70mph for hours and hours is very low strain on the engine that will be running nice and cool with all that airflow and isn't going to knock and you would notice no power difference.

Also while you are correct. Dyno conditions do generally...suck. Doing back to back pulls, there is a lot of heat buildup. And even with fans, it's no replacement for unlimited ambient air at 70+mph.

 

[JASmith]

A page from the new manual made available today... there are reccomandation about high altitude/ towing and ethanol.. for everybody to look at. In my situation, I will be fine with 87 Octane.

Yup, exactly, high loads and higher temps are more likely to cause knock, and so you'll benefit more from higher octane in those conditions. Not sure if I mentioned it here or another forum, but that's why I run 93 octane on my Ram 1500 during the summer months especially if towing because TX can get really hot and with an engine at ~150K miles its bound to be a bit carboned up which create hotspots that again are more likely to cause ping which the higher octane can abate.

But like any 2022 MY vehicle that says it recommends 91 or 93 octane such as the Ecoboost 2.0, it will run fine on 87 octane, but it may see reduced fuel economy and horsepower because of the way the system is protecting the engine from knock, generally running a bit richer and with altered timing that reduces power. There are limits to how much those tricks work though, so don't run 91 octane recommended Ecoboost 2.0 on below 87 octane fuel (which isn't even on most pumps anyway).

Regarding ethanol, they are just warning that this isn't a flex-fuel vehicle so not to run more than 15% ethanol, but typically for "normal" gas it will either be ethanol free or have only 10% ethanol which is low enough concentration its not going to mess with any fuel lines or components in the fuel tank like high ethanol fuel can for components not designed for it.

tl;dr: In the cooler months and if you're driving relaxed and not towing, save money and run your ecoboost on 87 octane. In the hotter months, when towing, when you want all the horsepower you paid for, or when mileage is getting high (especially on a direct injection turbo engine that is more prone to carbon deposits forming), run 91+. For the hybrid, just run 87 all the time.

 

[JASmith]

Also while you are correct. Dyno conditions do generally...suck. Doing back to back pulls, there is a lot of heat buildup. And even with fans, it's no replacement for unlimited ambient air at 70+mph.

If they did that, but I don't think they did or they likely would have mentioned that the horsepower was averaged on multiple consecutive pulls. It also would have shown even more benefit to premium fuel, and it was pretty clear the author was biasing the story to 93 octane being a waste of money.

 

[DesertSweat]

If they did that, but I don't think they did or they likely would have mentioned that the horsepower was averaged on multiple consecutive pulls. It also would have shown even more benefit to premium fuel, and it was pretty clear the author was biasing the story to 93 octane being a waste of money.

I would have hoped they would do multiple otherwise the data is moot. But if the author is biased, he did a poor job at convincing.

 

[fbov]

...is the general consensus that for the Hybrid ...?

None of the above.

So for the Maverick 2.5l is that not true?

Remember, the 2.5L is extremely high compression, because it's designed to underfill the cylinder on intake by definition of the Atkinson cycle. It varies the fraction underfilled as one of the control parameters, but with the goal of getting more energy out of less fuel. Most "high performance" modifications get more energy out of more fuel. That's the opposite goal.

Fuel economy would just decrease, because the energy density per gallon has changed, but with 10% its such an insignificant difference that no one would be able to tell by seat of the pants anyway.

Unless they drive a hybrid for high mileage. I don't want to double post the same data. I saw a consistent 5% in the C-Max. Haven't measured the Escape.
https://www.mavericktruckclub.com/forum/threads/whos-going-to-tune-for-20-ethanol.1132/post-19517

 

[Deleted member 1483]

I run my current 2.0 ecoboost using 89 octane (anything above 87). I have no numbers but there is some obvious line somewhere between 87 and 89 where the engine behaves better. I plan on using 87 in my new hybrid maverick as I believe the electric motor will prevent it from feeling 'gutless' more than any timing could.

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