Knock Factor and KF_KA_T_Komp

[samthejam]

I was able to get to look at a tune file from someone considered reputable on here.

Before loading it into my car, I decided to look through it to see what gets changed when these tunes are modified. I’ve got a few questions I’d like to get answered first.

Edited 4/10/25:
Removed pictures of these exact values for these table, as they were not needed for the relevant questions I had. Answers are only posted here now.

Knock Detection_KNOCK FACTOR / KF_KD_KFAKT_1

If you edit this value this will, edit the sensitivity of the knock sensors.

Going higher means the sensor is LESS sensitive.
Going lower means the sensor is MORE sensitive.





KF_KA_T_KOMP :
The values from a CSL can be substituted to make the DME less aggressive at pulling timing in relation to IAT and coolant temp.

[Slideways]

For knock factor, my understanding is a higher value lowers sensitivity. The values in the custom tune are ~20% greater.

[samthejam]

According to the tuner (document attached) the CSL has a Coolant Temp and IAT temp axis map that changes knock. The reasoning for using the CSL values, is it will just help it from pulling timing. I believe it is fair to say that is KF_KA_T_KOMP. Probably translates to Knock Temperature Compensation?

I do wonder how BMW was able to make this map less sensitive, were they just removing some safety they left on the table or with the airbox/cams it is just less likely to knock at higher temps for whatever reason. Or maybe it is because the IAT sensor is relocated so it's compensating for that?


Video is from an OE Calibrator describing how a table like that would usually be set.

https://www.youtube.com/watch?v=YudIx8Ux6OU&t=5696s


https://nam3forum.com/forums/forum/main-forum/e46-2001-2006/733-tuning-vanos-timing-and-ignition-timing-from-old-forum-full-txt-pdf

[samthejam]

For knock factor, my understanding is a higher value lowers sensitivity. The values in the custom tune are ~20% greater.

Thank You for clarifying!

[Bry5on]

Maybe it’s just me but I find it pretty uncool to 1) publish someone’s work online without permission and 2) flash a tune that you intend to use to your car that you didn’t pay the author for, and I guess also 3) publish someone’s work that you didn’t purchase.

You could easily ask these questions without publishing work, I’d recommend doing that at the very least.

[samthejam]

Maybe it’s just me but I find it pretty uncool to 1) publish someone’s work online without permission and 2) flash a tune that you intend to use to your car that you didn’t pay the author for, and I guess also 3) publish someone’s work that you didn’t purchase.

You could easily ask these questions without publishing work, I’d recommend doing that at the very least.

1. For a safety feature like this I felt it was okay to ask and get others opinions using the exact values. However you are correct it wasn’t needed to post the exact values. Cam timing, fuel and ignition I would not share.

2. This is fair.

3. I still have not said whose work it is explicitly to avoid it from being searched. The document is there, so if you want to dig it can be found. I wanted to share the source of where I got the information for the intension of using the CSL compensation settings.

I do see your point and apologize. I will edit original post to exclude the exact data and just inform what the maps are now that I know.

I spent a lot of time developing an eprom tune for my E28, and that did start with trying different tunes being unhappy. I was sold quite a few poor chips. I learned by seeing what they changed and then making my own changes. I understand how there is a lot of time editing these values to make a complete package to sell to the end user. Let alone the support side

[Bry5on]

1. For a safety feature like this I felt it was okay to ask and get others opinions using the exact values. However you are correct it wasn’t needed to post the exact values. Cam timing, fuel and ignition I would not share.

2. This is fair.

3. I still have not said whose work it is explicitly to avoid it from being searched. The document is there, so if you want to dig it can be found. I wanted to share the source of where I got the information for the intension of using the CSL compensation settings.

I do see your point and apologize. I will edit original post to exclude the exact data and just inform what the maps are now that I know.

I spent a lot of time developing an eprom tune for my E28, and that did start with trying different tunes being unhappy. I was sold quite a few poor chips. I learned by seeing what they changed and then making my own changes. I understand how there is a lot of time editing these values to make a complete package to sell to the end user. Let alone the support side

Thanks! Not knocking your process, I too have learned from other tunes in my journey. Glad to have folks here that are digging in to the details and self teaching. Get after it!

[R3VM3UP]

Couple thoughts on this:
1. When looking at something like KF_KA_T_KOMP, make sure you are looking at the total picture. In the non-CSL bin that I'm looking at, the base WOT ignition timing looks like it's earlier than the CSL. I'm quite sure that the result of KF_KA_T_KOMP is additive with the result of the base WOT ignition timing.

In the CSL bin, it looks like KF_KA_T_KOMP is equal to zero at 84degC coolant temp and 30degC intake air temp. I would interpret that as indicating that 84degC coolant temp and 30degC IAT were the setpoints at which the base spark table was calibrated. In the non-CSL bin, there isn't a cell where the table is exactly zero due to the chosen breakpoints, but it's calibrated such that the zero point is at a slightly lower coolant temp and/or IAT. If someone cared to interpolate the table further, that exact point could be determined pretty easily. To me this would suggest that the base ignition table in the non-CSL variant was calibrated at slightly lower temps, which I think explains at least part of the difference.

2. As you mentioned, another potential factor is that the CSL uses a different temp sensor in a different location. This inevitably results in slight differences in measured air temps which also seems like it could be playing a role here. Additionally, the CSL has slightly longer duration cams. All else being equal, later IVC means lower effective compression ratio. The longer exhaust duration may also help reduce exhaust residual on subsequent cycles which is beneficial for knock reduction. I would generally expect any impact from the cams to show up in the base tables though, not the temp modifiers.

3. I don't know much about the KF_KD_KFAKT_ maps so I can't comment much on those. Is this some sort of threshold for what amplitude of knock sensor activity is categorized as 'true knock'?


On the topic of intellectual property, I honestly think that tuning on this platform has been held back a bit by people being a bit overly concerned about this. I don't believe there is a single tuner in the game on any platform that is not guilty of copying someone else's tune at some point or another. Additionally, tuners are in a way, monetizing intellectual property of the OE and I think it could be argued that they don't have the right to do that in the first place. I'm no lawyer, but this sounds sorta like if someone were to change a few character names in a popular book and resell it as their own. Granted, there is no copywrite on the OE calibration, but it is protected by NDAs signed by anyone who worked on it or had access to related documentation. In almost every case, aftermarket tuning is made possible by someone breaching their contract and leaking OE intellectual property. Anyhow, I don't mean to derail this thread with a debate over who owns what IP, and I'm not advocating for anyone to post tune files purchased from 'pro' tuners, but it would be nice to see people delve a bit more into topics like this one, about actually calibrating the engine, not just the reverse engineering aspects.

[karter16]

Couple thoughts on this:
1. When looking at something like KF_KA_T_KOMP, make sure you are looking at the total picture. In the non-CSL bin that I'm looking at, the base WOT ignition timing looks like it's earlier than the CSL. I'm quite sure that the result of KF_KA_T_KOMP is additive with the result of the base WOT ignition timing.

In the CSL bin, it looks like KF_KA_T_KOMP is equal to zero at 84degC coolant temp and 30degC intake air temp. I would interpret that as indicating that 84degC coolant temp and 30degC IAT were the setpoints at which the base spark table was calibrated. In the non-CSL bin, there isn't a cell where the table is exactly zero due to the chosen breakpoints, but it's calibrated such that the zero point is at a slightly lower coolant temp and/or IAT. If someone cared to interpolate the table further, that exact point could be determined pretty easily. To me this would suggest that the base ignition table in the non-CSL variant was calibrated at slightly lower temps, which I think explains at least part of the difference.

2. As you mentioned, another potential factor is that the CSL uses a different temp sensor in a different location. This inevitably results in slight differences in measured air temps which also seems like it could be playing a role here. Additionally, the CSL has slightly longer duration cams. All else being equal, later IVC means lower effective compression ratio. The longer exhaust duration may also help reduce exhaust residual on subsequent cycles which is beneficial for knock reduction. I would generally expect any impact from the cams to show up in the base tables though, not the temp modifiers.

3. I don't know much about the KF_KD_KFAKT_ maps so I can't comment much on those. Is this some sort of threshold for what amplitude of knock sensor activity is categorized as 'true knock'?


On the topic of intellectual property, I honestly think that tuning on this platform has been held back a bit by people being a bit overly concerned about this. I don't believe there is a single tuner in the game on any platform that is not guilty of copying someone else's tune at some point or another. Additionally, tuners are in a way, monetizing intellectual property of the OE and I think it could be argued that they don't have the right to do that in the first place. I'm no lawyer, but this sounds sorta like if someone were to change a few character names in a popular book and resell it as their own. Granted, there is no copywrite on the OE calibration, but it is protected by NDAs signed by anyone who worked on it or had access to related documentation. In almost every case, aftermarket tuning is made possible by someone breaching their contract and leaking OE intellectual property. Anyhow, I don't mean to derail this thread with a debate over who owns what IP, and I'm not advocating for anyone to post tune files purchased from 'pro' tuners, but it would be nice to see people delve a bit more into topics like this one, about actually calibrating the engine, not just the reverse engineering aspects.

FYI base WOT ignition timing is only one of a number of maps that goes into calculating ignition timing (and that's before dynamic advance and all that comes in) it is selectively used based on operating mode. Not saying your reasoning re the cause for the difference between CSL and non-CSL is wrong - I haven't looked at it in enough detail to be able to say - but it's certainly not as simple as KF_KA_T_KOMP being added on top of the WOT map. KF_KA_T_KOMP is one of six or so maps that feeds into generating KA_DTZ on a per-cylinder basis and this in turn is one of the factors that feeds into retarding the calculated ignition angle (of which the base WOT map is again one input of many).

As always with much caution that the funktionsrahmen is incomplete and outdated in numerous ways, 8.1 Ignition and 8.02 Dynamic Lead here: https://github.com/karter16/CSL_0401...ted%20(English) are worth a read to get a feel for the key building blocks to how the ignition timing is built out.


Sent from my iPhone using Tapatalk