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      02-12-2013, 02:56 PM   #1
M3takesNYC
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Factors inducing knock and reading it with BT

A related data-logging thread for those more knowledable than me on this s65 or even the s85 engine regarding which value on the BT tool are we using to identify knock? Quite literally there are about 5 or 6 parameters relating to knock in some fashion and the units are not making sense to me. Often in the KW and giving numbers in the 6000 range when knock does register. A good reliable value with the BT tool and the meaning of the value would be greatly appreciated.

Also I was wondering what else determines knock. I tried to do some more structured testing and used 100 octane to do some runs, IAT's were low and yet there is still some knock in the 7900-8200 range that shows up. However I have no idea how much timing its pulling as the values do not make sense to me. The road was consistently on incline which may have put the load on the engine and caused knock but the timing was hitting its targets for the tune.

So essentially if you are hitting timing targets and IAT's are cool, are these engines that sensitive to still be riding along the knock sensor and intervening even at low rates?

I realized now after logging how bmw was able to be so aggressive with timing targets as the ability of this system to register minute changes is so fast that it can constantly test the max timing to get as close as possible.
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      02-12-2013, 03:00 PM   #2
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I'll participate in this. Would be great to see data from a cross section of cars.
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      02-12-2013, 04:00 PM   #3
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PencilGeek has a BT Tool config file you can download from his web
site that will log timing and IAT.
http://www.rcollins.org/public/Bavar...estWithIAT.xml
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      02-12-2013, 04:06 PM   #4
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Timing and IAT are not a problem. Those are straightforward and labeled. Same with AFR and everything else. It is knock that is not clearly labeled or atleast to me.
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      02-12-2013, 04:34 PM   #5
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Quote:
Originally Posted by m33 View Post
PencilGeek has a BT Tool config file you can download from his web
site that will log timing and IAT.
http://www.rcollins.org/public/Bavar...estWithIAT.xml
Thank you! Looking forward to using this.
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      02-12-2013, 04:58 PM   #6
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Quote:
Originally Posted by signes View Post
Thank you! Looking forward to using this.
no problem ! It's cool and
Useful and if you do it enough you'll be able to generate a graph in 5 min..

Robert is a helpful great guy!
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      02-12-2013, 05:00 PM   #7
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The problem with the BT tool is it only data logs one cylinder at a time..so your are only able to see a partial picture of what is going with detonation in the engine.
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      02-12-2013, 05:13 PM   #8
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My understanding is that it does it by bank?
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      02-12-2013, 06:09 PM   #9
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Quote:
Originally Posted by signes
My understanding is that it does it by bank?
Timing retard is done per individual cylinder.
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      02-12-2013, 10:45 PM   #10
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Mike do you know which value to use to identify knock? So many variations.

Any thoughts on causes of knock.

For example, even if you have ample octane, and good IAT but have a high load like a decent size hill, is the mapping automatically pulling timing simply because measured load is X even if no detonation is occuring because octane is high and IAT's are low enough? That doesn't pertain to my knocking question but rather what reasons would you not hit your timing targets if your IAT and octane are good (meaning 100 octane or something)?

Related is given good IAT and octane fuel, what other than perhaps load would cause knock to show up?
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      02-12-2013, 11:33 PM   #11
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Since this is an Ionic knock sensor system it's hard to see what outside contributing factors are seeing/allowing knock sums to be detected. This is a very advanced/complex design that has the ability to pul timing per cyliner (I believe).

Traditional knock sensors sometimes hear "phantom" knock which is not actually knocking but (example: something rattling against engine block) a outside factor that makes the engine think it's knocking and thus pull timing.

You really need to see how much knock the car is seeing and then how much timing is being pulled. IMO the car will see a few knock counts as the car can/does have aggressive mapping and can do so due to the advanced knock sensor design. While the car runs very aggresive targets the result is small knock sums that may pull timing a few degrees but IMO this wouldn't be harmful at all. If the car really starts pulling timing there is def an issue. I would really rather see 0 knock though.
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      02-12-2013, 11:54 PM   #12
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That is my point that although a few runs had virtually no knock, there were several runs which hit timing targets roughly 33-34 around 7500 plus RPMS, IATs were ice cold and a cold night and 100 octane in the tank. All of the possible controllable factors yet knock still showed up. Clearly since timing was still close to the targets with a tune (although I don't know the exact targets with this tune) I figure the knock was very subtle. It also was only for the 7500-8k range and than 8k-8500 had no knock, which also seemed strange until I realized maybe the VE above 8k is better and perhaps that has something to do with less knock.

Very complex engines indeed!

By the way AFR's were spot on. So my point is if knock still happens in these ideal conditions, I hate to see what kind of knock is actually going on in the dead of summer on 91 octane. Almost scares me! Sometimes too much information is not a good thing!
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      02-13-2013, 02:41 AM   #13
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Ummmm .... what are we supposed to be scared of? to sum it up for the rest of us?
What about all those guys running boost and heatsoaking in the summer? If this is something serious then we should have heard something by now.
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      02-13-2013, 11:01 AM   #14
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There is nothing to be scared of! I was just explaining there is something psychological about seeing data on a screen showing a car is knocking even under "prime" conditions. Makes me think of the hot summer days and how much knock must be working over time!

In the end it is simply not relevent, not dangerous and that is what the engine is made for, to compensate for any conditions with no damage to the engine. It was more of a situation where actually SEEING it is a bit different than just knowing it probably happens.

Not dangerous, just was interesting to see the sensitivity. Nobody has anything to worry about!!
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      02-13-2013, 11:27 AM   #15
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Quote:
Originally Posted by Superfly_M3 View Post
Ummmm .... what are we supposed to be scared of? to sum it up for the rest of us?
What about all those guys running boost and heatsoaking in the summer? If this is something serious then we should have heard something by now.
WTF? Who said anything about being scared? It is an interesting topic to understand how the engine management system work (or for those like me trying to get better data around variances in power figures for different dyno runs.)
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