Ford Ecoboost and the Octane Adjust Ratio Monitor

All Ford Ecoboosts use a dynamic multiplier known as Octane Adjust Ratio.  This parameter can be monitored with the Accessport and is helpful in ensuring the fuel in your tank is adequate.  It is especially important on an Ecoboost vehicle when peak power is expected (dyno tuning, racing) to make sure the parameter is at the optimal -1.0 value.

Strategy Background
This vehicle is equipped with several dynamic load, airflow, and torque targeting and limiting strategies.  These strategies allow the vehicle to achieve consistent performance with varying atmospheric conditions and fuel quality.  There are no set “boost targets” with these strategies, and as such boost pressure can vary depending on driving conditions.
How It All Works
From the factory, Ford typically designs the base calibration to allow use of 87+ octane fuel and recommends using 91+ octane fuel for optimal power.  They can do this by means of a dynamic multiplier that allows for adjustment of each of these targeting and limiting strategies which we call the “OAR” (Octane Adjust Ratio).  The OAR starts life at a value of 0.0 and is allowed to learn in two directions.  When fuel quality and knock sensor feedback are optimal, the OAR will adjust towards -1.0.  When these are sub-optimal, the OAR will adjust towards +1.0.  I bet you’re wondering why -1.0 is better?
Well for one, since this value is a multiplier and not an offset the ECU code can be optimized to use a single table comprised of negative values to handle the spectrum of operating conditions.  Take ignition timing corrections for example; with an OAR at -1.0, multiplying against a negative becomes positive which is then added as positive correction to ignition timing.  However, when conditions are sub-par a +1.0 OAR will result in negative correction to ignition timing.
How Does It Effect Power?
Additionally, the OAR is used in other strategies such as LSPI (Low Speed Preignition), and part-throttle combustion stability.  These are functions designed to dynamically limit load production in the event that fuel quality is not optimal.  We want the ECU to limit load as it will remove stress and prevent damage automatically.  The part-throttle limiter allows for casual driving at moderate loads while maintaining stoichiometric operation.  This allows for increases in fuel mileage but at the expense of heat.  Heat is generated much more quickly with lower octane fuels and can cause detonation. This is why it is necessary for the OAR to step in and allow for adjustment.  In the case of LSPI, the OAR is used to create a blending ratio between three separate load limits to mitigate the possibility of preignition.
How Does COBB Use OAR?
Our calibrations attempt to utilize as many of the OEM strategies as possible to offer the most advanced, powerful, and safest driving experience to you.  Most of our calibrations utilize the OAR just as the factory does.  However, our calibrations are designed for a specific octane rating and have a no nonsense policy for knock.  If the ECU senses knock, we will aggressively adjust the OAR towards positive. We have designed the OAR to be utilized so that maximum performance is achieved for the specified octane.  This is why it is important to run the appropriate calibration for your available fuel type!  The OAR is also a KAM (keep alive memory) stored value and will be reset upon initial installation of the Accessport.  It will take time to learn, so don’t be alarmed after a few days of driving if it’s not fully settled.  Once learned, the value will persist through each start-up (even through “change map”).  The value may change from time to time based on knock sensor feedback, which is completely normal and expected.  If you find the OAR value does not stay near -1.0 when using top tier fuels, please use the Accessport to change to a lower octane calibration until better fuel can be found.


COMMENTS
Kevin Smith on July 9, 2015 says:

I have the OAR displayed on the AP and it is consistently running at -1.5. According to the article it should be about -1.0. Should I be concerned?

Reply
    Marshall
    Marshall on July 13, 2015 says:

    Hey Kevin, it sounds like you may have the wrong monitor selected as -1.0 is the limit for OAR. Double check that you have the correct monitor selected, and if you’re still seeing odd values send an email over to our Customer Service team at support@cobbtuning.com.

    Marshall@COBB

    Reply
      Mark Dunstan on October 27, 2015 says:

      I have the same issue…. Only mine is showing -0.18.

      Reply
        Kyle
        Kyle on October 29, 2015 says:

        Hello,

        If the value isn’t -1.0, you need better gas. Even with 93 in the tank, it will take an amount of driving and putting the car through different situations to bring the value to the optimal -1.0.

        Kyle@COBB

        Reply
Remon Medhat on October 14, 2017 says:

If the OAR is the same as stock values do that mean that i can use the stock recommended octane ? or even if the OAR and lets say we raised the boost then will need to get a better octane? thanks

Reply
    Kyle
    Kyle on October 16, 2017 says:

    Hi Remon,

    The number in the map name indicates the minimum octane fuel that can be used. Any custom tuning may or may not require higher octane.

    Kyle@COBB

    Reply
      Remon Medhat on October 17, 2017 says:

      thanks for replying ,so if my car’s oar is -1 does it run better ( in terms of performance ) than -0.5 ? or does they produce same power but it shows the room for power in the tune ?

      Reply
        Kyle
        Kyle on October 17, 2017 says:

        Yes. If it is at -1.0, that will be optimum performance. Anything from -.99 to +1 means the car is pulling timing making less power.

        Kyle@COBB

        Reply
Remon Medhat on October 25, 2017 says:

Heyy, so on 92 my oar is around – 0.4,-0.5 on 95 it is now – 0.57 and still learning, will putting 92 will make less power only and no damage to the engine at all? Also how much is the difference (average) between 92 and 95 RON on the oar?

Reply
    Kyle
    Kyle on October 25, 2017 says:

    Hi Remon,

    The worse the OAR (closer to +1) the less power you’ll make. The number in the map name is the minimum octane fuel that should be run in AKI. This is the US measurement of octane. If you’re using RON fuel you’ll need a minimum of 95 RON to run the 91 maps and 98 RON to run the 93 maps. While the car SHOULD pull timing if you have lesser than adequate fuel for the map you’re running I would not recommend relying on it to do so. If it doesn’t, or even does pull appropriate timing but not fast enough, engine damage can occur.

    Kyle@COBB

    Reply
Remon Medhat on November 22, 2017 says:

Hey Kyle, if on a stock tune with the best octane found in my country which is 95 ron my oar is around – 0.8x at its best by far, would tuning my car i will have better performance or not that much?
Also if the temp and fuel is the same but one time i keep hooning ans one time rpms below 3 k will the 2nd time record better oar number?

Reply
    Kyle
    Kyle on November 22, 2017 says:

    Hello,

    You would have better performance using the 91 maps on your 95 RON fuel than stock. There is a learning process to OAR. As you put the car through different situations OAR will adjust to the point up to where some detonation is present. The number will not get better if the car is seeing detonation.

    Kyle@COBB

    Reply
Remon Medhat on March 7, 2018 says:

Hey, i do own a Ford vehicle but there is no support for it, it is the focus 1.5 ecoboost, the question is if on stock tune i achieve like – 0.7 to -. 08xx, will tuning my car be a very bad idea cuz i am not even getting the max performance from my stock car and tuning will damage the engine?
I am using torque app for the oar and knock, also i see knock on idle, is this app authentic? Thanks!!

Reply
    Kyle
    Kyle on March 7, 2018 says:

    Hi Remon,

    The relative safety of a tune depends on the tune. It’s possible to tune the car safely even with a less than optimal OAR. I’m not sure about the app you’re using being accurate – I’ve never heard or used it before.

    Kyle@COBB

    Reply
Marc Bernat on January 11, 2019 says:

How does winter gas effect the OAR? The best I’ve seen when starting to monitor this is -.74 and as we get further into winter even with Shell 91 (no ethanol) I’m seeing -.57 numbers. Hoping once we get into spring time and they switch to a summer gas then the number will correct to -1. If the spark plugs are worn or gapped incorrectly can this effect OAR too?

Reply
    Marshall
    Marshall on January 11, 2019 says:

    Hey Marc, utilizing non-ethanol 91 octane fuel is likely the cause of your OAR values. In our experience, that fuel typically produces behavior more in line with ~89 octane fuel that contains 10% ethanol. If possible, I would definitely recommend seeking out a higher quality fuel to maximize performance. Otherwise, the knock detection system is doing its job!

    Marshall@COBB

    Reply
Remon Medhat on January 17, 2019 says:

hey, i wonder if the OAR is a multiplier for the ignition timing only ? and that the Boost , AFR or anything else is not changed by the OAR strategy .

Reply
    Kyle
    Kyle on January 17, 2019 says:

    Hi Remon,

    The OAR won’t directly change other parameters but boost and AFR are affected by timing changes. So, kind of, but indirectly.

    Kyle@COBB

    Reply
Jordan Stempleman on April 19, 2019 says:

Question about fuel quality. I’m running Stage 1 91 octane. Where I live the two options I have for top tier gas are 93 no ethanol and 91 with up to 10% ethanol. Which gas would be best for my my tune/car?

Thank you!

Reply
    Kyle
    Kyle on April 19, 2019 says:

    Hi Jordan,

    The maps are created with fuel that contains up to 10% ethanol. That is what should be used. I’d recommend the 91 e10 fuel for the 91 map over the 93 e0 option.

    Kyle@COBB

    Reply
Dominik Vaughan on May 2, 2019 says:

If I am running the stage 0 stock tune is it possible to run 87 octane in the car and still get a -1.00 OAR

Reply
    Kyle
    Kyle on May 2, 2019 says:

    Hi Dominik,

    It hasn’t been tested so I can’t say for sure. My guess would be probably not though.

    Kyle@COBB

    Reply
Benjamin Doherty on September 6, 2019 says:

What kind of changes will I see to the OAR if I am running an ethanol blend like an e20, e30, or e40? with running an ethanol mix I would think that it would definitely change the OAR. Your advice is appreciated, thanks.

Reply
    Adam Hill
    Adam Hill on September 9, 2019 says:

    Hi Benjamin,

    Good question. Ultimately you want OAR to stay at its ideal value as much as possible no matter what fuel type you are using. Just keep in mind that if you are using a blend at E20 or higher, you do need custom tuning and also keep an eye on fuel trims considering that ethanol does require higher flow.

    Adam@COBB

    Reply