Quote:
Originally Posted by alf
This is a very interesting aspect. The altitude in the region I am concerned about is between 900m and 1400m, so it is not exactly see level. I will definitely run some tests with 87 at higher elevation, just to better understand what is happening. Thanks for the info.
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Not sure if 900 meters is enough to have a significant effect. I was thinking more if your plans were to drive in the Rocky Mountains or something like that (2000+ meter). On the other hand, the pressure drop is exponential with the largest drop off at lower altitudes. So it might be worth looking a bit into it.
Regarding logs. Actual knock events are not logged at all. The only thing the ECU is logging is response to what the ECU percieves as being precursor to knock. I.e. the engine never actually knocks, as the ECU preemptively removes timing.
What is being logged, is how much timing the ECU preemptively takes out. The system is so effective, that renowned authorities in tuning says it's not necessary to use knock-ears when tuning Subaru engines and you can fully rely on the ECU logic to take out timing. Most ECU tuning is done per E-tune as well where the tuner never sees the car, let alone would be able to get their ears in the machinery.
As such, it's a matter of not maxing out the capabilities of the system from a safety aspect and minimizing it's intervention for performance optimization. Typically the ECU will remove more timing than necessary and a better result can be achieved by removing a smaller amount from the timing tables.
Anyway, when you look at the logs and see FLKC, it doesn't mean the engine is knocking. Rather that the ECU is taking messures to avoid knocking. Also it stands for Fine
Learning Knock Correction. So if you see the same value, e.g. -2 deg at 4000 rpm and load 1.0 all the time, it just mean the ECU
once decided to remove the timing and didn't deem that it could reinstate it for the following occurances.
Short version, there is nothing wrong with seeing FLKC here and there if it's of random nature and not excessive values. If you were to take out timing to the point where there is never FLKC, you would need to detune the engine immensely and it would defeat the point of having a system that ensures we can run the optimum timing most of the time.