Octane Adjust Ratio, Decrease Global Timing

[DSMtuned]

At this point I'm tweaking E-tunes on my SCT Livewire to the extent possible for my 3.5 Ecoboost F-150.

I noticed my octane adjust ratio was at -.30 with a new tune. Would I be correct to assume that decreasing global timing a couple degrees would bring that OAR closer to -1?

My understanding is that the OAR is a multiplier that is used to figure total timing. So if all other variables equaled 18* BTDC timing, and the OAR is -.30, then -18*x-.30=5.4* BTDC as the final timing. If the OAR is -1 then -18*x-1=18*.

It seems like you want your OAR as close to -1 as possible for the most timing and best power. Am I on the right track here?

[sc544x4f150]

You do want it as close to -1 as possible but it functions a lot different that what you suggested. It is a multiplier against the octane adjustment table then added to the borderline knock calculation. For example if the borderline knock tables output is 18*, octane adjustment tables output is -5, and the OAR is -.30 then your math would look like this: 18+(-.3X-5)=19.5* or 18+1.5=19.5*. So in that scenario the ECM adds 1.5 degrees to the borderline knock calculation. The other function of the OAR is to determine the LSPI limits. There is three LSPI tables: Low, Nominal, and High. These tables have the maximum air load the engine is allowed to reach based on RPM and manifold charge temperature. The Low table has lower load limits for lower octane fuels and the high has higher load limits for higher octane fuels. At an OAR of -1 the high table is weighted 100%, at an OAR of 0 the Nominal table is weighted 100%, and at an OAR of 1 the low table is weighted 100%. If your OAR is in between those numbers the ECM blends the tables together. Correct LSPI load limits is crucial to avoiding engine damage. I wouldn't trick the OAR just to get to -1. The correct way would be to increase your octane. Now for me I had OAR values all the way to -1 on 87 octane which would not support the load limits in my high LSPI table without preignition. To fix this I datalogged the areas of the borderline knock tables that had negative knock retard and added in timing to get my OAR to positive values and decreasing my load limits. When I'm injecting water-meth or have higher octane fuel in the tank the OAR goes more negative adding timing and increasing the load limits.

[DSMtuned]

You do want it as close to -1 as possible but it functions a lot different that what you suggested. It is a multiplier against the octane adjustment table then added to the borderline knock calculation. For example if the borderline knock tables output is 18*, octane adjustment tables output is -5, and the OAR is -.30 then your math would look like this: 18+(-.3X-5)=19.5* or 18+1.5=19.5*. So in that scenario the ECM adds 1.5 degrees to the borderline knock calculation. The other function of the OAR is to determine the LSPI limits. There is three LSPI tables: Low, Nominal, and High. These tables have the maximum air load the engine is allowed to reach based on RPM and manifold charge temperature. The Low table has lower load limits for lower octane fuels and the high has higher load limits for higher octane fuels. At an OAR of -1 the high table is weighted 100%, at an OAR of 0 the Nominal table is weighted 100%, and at an OAR of 1 the low table is weighted 100%. If your OAR is in between those numbers the ECM blends the tables together. Correct LSPI load limits is crucial to avoiding engine damage. I wouldn't trick the OAR just to get to -1. The correct way would be to increase your octane. Now for me I had OAR values all the way to -1 on 87 octane which would not support the load limits in my high LSPI table without preignition. To fix this I datalogged the areas of the borderline knock tables that had negative knock retard and added in timing to get my OAR to positive values and decreasing my load limits. When I'm injecting water-meth or have higher octane fuel in the tank the OAR goes more negative adding timing and increasing the load limits.

Thanks for the response. Would you consider adjusting global timing by -2* as, "tricking" the OAR? Remember for now, I'm adjusting tunes with the SCT Livewire or having my e-tuner recalibrate, which is not a streamlined process.

[metroplex]

If I'm using fuel that doesn't seem to be very good or lower octane fuel, the OAR gets further away from -1. E20-E30 is almost always -1 (pegs it out) and inferred octane is 98.

[sc544x4f150]

I would consider taking -2 degrees out using the global adder to be cheating the OAR because the OAR may now be lower than it should be. And now you have two less degrees of timing until the OAR adds it back in.

[DSMtuned]

I would consider taking -2 degrees out using the global adder to be cheating the OAR because the OAR may now be lower than it should be. And now you have two less degrees of timing until the OAR adds it back in.

Fair enough. Thanks for the input.

[NickSezz]

Make sure you are driving around long enough for the OAR to fully adapt. I logged while driving around (this takes time) with premium fuel and pulled out timing from borderline tables to reflect what the knock sensor was doing. Most of the time I was pulling out timing from 2000-3500 rpms between .60 and 1.30 load. Once this was done OAR moved to about -.96 adding most of the 5 degrees from the octane modifier table to borderline calculations. One advantage I noticed from doing this was seeing higher timing during WOT runs without having to add it into the borderline tables or waiting for the knock sensor to ramp it in (if allowed). Set up this way, I am getting to most out of the fuel in my area. If fuel quality degrades it will adapt, but if I move to a high octane fuel I need to make a tune change.