Dear Gents (and Ladies of course). I'm starting a discussion about.... you guessed it, knock! More importantly, tuning strategy to avoid knock and what levels of knock are considered acceptable.
I want to start out by stating some points and hopefully we can all pitch in information and clarify based on real world experience, some tuning strategies and how to keep our engines running safe and strong.
I will keep updating this thread as new information/experience comes in.
Please, only contribute if you have real world experience. Let's try to refrain from re-posting other things that are commonly said on the internet because I want to avoid the broken telephone effect and shatter some common myths and bring clarity about the subject.
1). A lot of tuners and big OTS map companies (Such as COBB) suggest that Fine Learning knock is completely acceptable and recommend their users to basically ignore it unless it's over x... amount (As long as DAM/IAM doesn't decrease)
-Although Feedback Knock is a response to a single knock event and catches false knock all the time, Fine Learning Knock, registers due to persistent knocking in a specific region of the map.
-Once a fine learning value is "learned" by our ECU, the Timing is pulled for that area of the map and stays there until it is unlearned, slowly over a period of time, unless knocking in that area of the map persists in which case it will go back up.
-Fine learning of say -2.81 degrees means -2.81 degrees will ALWAYS be pulled from that area of the map UNTIL that area of the map is unlearned. My understanding is that if the car is always over 2 degrees (for example) of timing, that's a HUGE power tax on that cell.
-FLK affects LARGE areas of the map. By that I mean, each cell in learning view is nearly 1k in RPM range, and varies in load, but anywhere from .2 to 1 unit of load.
-FLK can be fixed in said cell by pulling only -.5 degree of timing a lot of the time (or even less). -.5 degrees of timing is significantly better than 1.4 or 2.8 or even 4.2 degrees of FLK.
2). DAM/IAM What is it? Is it a good indicator of a healthy motor?
(Copied from RomRaider website)
"Ignition Advance Multiplier (Dynamic Advance Multiplier on AP)
The ECU can adjust IAM in response to knock, and this value is used to scale the entire timing advance map. Because it effectively adjusts the entire timing map at once (as opposed to adjusting for a single RPM/load cell), it is presumed to be intended to compensate for varying fuel quality (e.g. if the owner fills up with low-octane fuel).
IAM is just one of several variables that contribute to the total ignition timing.
On 16-bit Subaru ECUs, IAM is an integer that varies between 0 and 16.
On 32-bit Subaru ECUs, IAM is a floating-point value that varies between 0 and 1."
3). Fine Learning Knock in low load cells VS full throttle cells
-FLK in lower load cells occurs during weird types of knock, such as tip-in knock (rapid changes in gas pedal position), EGR, false knock.
-It is safe to say (please correct me) that seeing any FLK in low load areas, is not anywhere as bad as high load (WOT) areas of learning view.
-(to me) it seems safe to also assume that ANY Fine Learning... OR persistent and regular Feedback knock (during smooth operation and gradually introducing WOT, rather than just pounding on the car) is not a good thing.
I will add more as it comes! Thanks for participating!