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Author Topic: Acceptable limits for knock voltage  (Read 94577 times)
britishturbo
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« Reply #60 on: January 23, 2013, 11:28:39 AM »

They all do, just before they melt the engine.
Every engine will make the most power with some knock, it just won't live very long.
And you have verified this using headphones on a load bearing dyno?

Haha that is very true.
No to the use of a load bearing dyno... I don't have easy access to one, that sure would be nice though!
The ecu is still pulling timing, and I have also reduced the requested timing in the areas that would start the knock retard anyway, I forgot to mention that.
The biggest change between the stock knock regulation and how it is behaving now is that the retard gets limited on the top end more which helps with top end power.

I'm actually planning on making a DIY DetCan this weekend and checking things out.
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nyet
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« Reply #61 on: January 23, 2013, 11:39:39 AM »

The biggest change between the stock knock regulation and how it is behaving now is that the retard gets limited on the top end more which helps with top end power.

That sounds very bad. Request less timing, don't numb KR.
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« Reply #62 on: January 23, 2013, 11:44:22 AM »

Haha that is very true.
No to the use of a load bearing dyno... I don't have easy access to one, that sure would be nice though!
The ecu is still pulling timing, and I have also reduced the requested timing in the areas that would start the knock retard anyway, I forgot to mention that.
The biggest change between the stock knock regulation and how it is behaving now is that the retard gets limited on the top end more which helps with top end power.

I'm actually planning on making a DIY DetCan this weekend and checking things out.

So the answer is no then. You are basically just randomly +20%-ing maps without really understanding what you are doing.
Turning off knock adaptation I also do not see the point in.
If you read about how the knock control works in these, you will see that it has a reference level. In fact two reference levels, one for the louder cylinders and one for the quieter cylinders. And knock is detected based on deviation.
The knock control is calibrated from factory using in-cylinder pressure sensors. In fact the FR lists the pressure spikes in bar that need to be recognized by the knock control.

Calibration might be needed when changing pistons and so on, but with stock pistons, especially at the upper level of the range, the factory knock control can usually hear the knock before, or at the very edge of where you can due to the engine being very noisy.
Of course this can no longer be correct if the engine has forged internals for example, but just +ing up the maps like you are just means that your engine is most likely running with some knock in the upper rev range. And yes, of course that will make more power...
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britishturbo
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« Reply #63 on: January 23, 2013, 11:54:26 AM »

Wow relax guys... more than anything I have been experimenting with the knock control... the numbers I posted above are my latest test.
I HAVE been reducing the timing requested and tweaking AFR in the areas that would cause the knock retard in the first place.
But what I have found from many many logs is that even though the knock voltages would then drop way down after that at higher rpms the ecu would still keep the retard that it got at first through the wot pull. The result was numb timing values at high rpms.

I've been experimenting with the different settings to try and reduce this effect.
I plan to also experiment with DetCans as well.

I was trying to stir up some debate on this matter because there is very little info out there.
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britishturbo
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« Reply #64 on: January 23, 2013, 12:01:16 PM »

Oh and the adaption was turned off after much discussion on the matter with phila_dot, he was actually the one who suggested it.
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prj
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« Reply #65 on: January 23, 2013, 04:39:03 PM »

But what I have found from many many logs is that even though the knock voltages would then drop way down after that at higher rpms the ecu would still keep the retard that it got at first through the wot pull.
Knock voltages are not relevant at all.
They only show you how noisy your engine is, they have little to do with the ECU detecting knock.

I don't think you quite understand the theory behind how an engine control unit detects knock...
Looking at absolute values is a complete waste of time, you are looking for a spike within the measuring window, a deviation from the normal levels.
There is a reason why these data acquisition devices with pressure sensors cost a fortune.
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britishturbo
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« Reply #66 on: January 23, 2013, 04:41:48 PM »

Knock voltages are not relevant at all.
They only show you how noisy your engine is, they have little to do with the ECU detecting knock.

I don't think you quite understand the theory behind how an engine control unit detects knock...
Looking at absolute values is a complete waste of time, you are looking for a spike within the measuring window.
There is a reason why these data acquisition devices with pressure sensors cost a fortune.

I've been tuning turbo cars for over 10 years and was involved in megasquirt code development so I know a thing about two about knock...

Just because I'm new here doesn't mean I'm an idiot.
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prj
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« Reply #67 on: January 23, 2013, 04:51:34 PM »

I've been tuning turbo cars for over 10 years and was involved in megasquirt code development so I know a thing about two about knock...

Just because I'm new here doesn't mean I'm an idiot.

I am not saying you are an idiot, I am pointing out that your reasoning shows lack of understanding.
Reducing or advancing timing and so on is not too relevant to calibrating knock control. Knock control calibration is going to first and foremost depend on the engine hardware, engine revolutions and cylinder charge.

As for ECU maintaining timing retard - there are variables for how soon it steps timing out and back in.
You are blindly adjusting thresholds instead.

Fact is, you are now running up top with some knock. You can reduce the time after which the ECU will phase timing back in, but if you phase timing back in too soon, then the cylinder temps will still be high from previous knock events and you are going to go right back into knock.
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ddillenger
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« Reply #68 on: January 23, 2013, 04:55:30 PM »

I really love nefmoto.

That is all.
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britishturbo
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« Reply #69 on: January 23, 2013, 06:13:56 PM »

I defined these maps in my xdf some time ago.  I'm looking at tuning them soon, as I think the ECU is too sensitive to knock from what i have found listening through det cans.

Rick

Rick and others here have previously said what I am saying. That the factory setup is too sensitive.
In my experience this is always the case with factory tunes. They tend to be on the safe side of knock, pulling timing at the very first time.
Just my experience and my observations. You don't have to agree with them...

But let me ask this. Who here has put set cans or sensors on the engine and compared the factory knock tune to audible knock that they could detect? Its one thing to say leave it stock and dong mess with it... but its entirely different to say that based on testing and data.

Thoughts?
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ddillenger
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« Reply #70 on: January 23, 2013, 06:19:30 PM »

I think PRJ is probably the best possible person to have answer that BT.
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britishturbo
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« Reply #71 on: January 23, 2013, 06:22:13 PM »

I think PRJ is probably the best possible person to have answer that BT.

I'm hoping prj will answer that without yelling at me haha :-)
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prj
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« Reply #72 on: January 23, 2013, 07:37:12 PM »

Rick and others here have previously said what I am saying. That the factory setup is too sensitive.
In my experience this is always the case with factory tunes. They tend to be on the safe side of knock, pulling timing at the very first time.
Just my experience and my observations. You don't have to agree with them...
You can adjust the amount of timing it pulls, but you are not adjusting that.
What you are messing with is the ECU's definition of knock.
The maps you are changing are not timing pull or amount to pull. The maps you are changing tell the ECU whether knock has occurred in a cylinder or not.
Either the flame front propagates through the cylinder uniformly or it doesn't.
If you want to modify how the ECU reacts to detected knock, then you are tuning the wrong maps! This is my point from the start.
I don't see how it's possible to dial in these maps cautiously or not cautiously - the OEM has pressure transducers hooked up to each cylinder, and they can exactly see when a spike occurs, and this is what they calibrate them to. If a reasonably sized spike occurs you are probably not going to make more power, because the peak is likely going to be before TDC.

Quote
But let me ask this. Who here has put set cans or sensors on the engine and compared the factory knock tune to audible knock that they could detect? Its one thing to say leave it stock and dong mess with it... but its entirely different to say that based on testing and data.
I've done this plenty of times on many different engines. And there are different factory calibrations as well.
I have experienced sometimes that the ECU detects knock when none is present, but that is usually on tunes where the engine block is not even the same...

I think what you want to tune in your case is the way it reacts to knock, not how it detects knock.
KFKEF are coefficients which basically tell the maximum permissible deviation from the base levels. The only right way to tune those is with in-cylinder pressure transducers.
You can do headphones and a multiplicative addition in a pinch, but I would not touch those until you verify that the ECU is seeing knock where there is none.

Look at the KRRA module, specifically KRFKN/KRFKLN, which tells how much to retard on a single knock event, as well as KRVFN/KRLVFN/KRVFSN, which is the speed at which the ignition angle is phased back in.
You can try to reduce the amount if pulls right off the bat, but if the amount you pull is not enough the first time, and you end up pulling more the 2nd time, you will lose power. As the cylinder heats up more and more due to knocking combustion, the fuel will be more and more prone to detonation.
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britishturbo
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« Reply #73 on: January 23, 2013, 09:11:03 PM »

You can adjust the amount of timing it pulls, but you are not adjusting that.
What you are messing with is the ECU's definition of knock.
The maps you are changing are not timing pull or amount to pull. The maps you are changing tell the ECU whether knock has occurred in a cylinder or not.
Either the flame front propagates through the cylinder uniformly or it doesn't.
If you want to modify how the ECU reacts to detected knock, then you are tuning the wrong maps! This is my point from the start.
I don't see how it's possible to dial in these maps cautiously or not cautiously - the OEM has pressure transducers hooked up to each cylinder, and they can exactly see when a spike occurs, and this is what they calibrate them to. If a reasonably sized spike occurs you are probably not going to make more power, because the peak is likely going to be before TDC.
I've done this plenty of times on many different engines. And there are different factory calibrations as well.
I have experienced sometimes that the ECU detects knock when none is present, but that is usually on tunes where the engine block is not even the same...

I think what you want to tune in your case is the way it reacts to knock, not how it detects knock.
KFKEF are coefficients which basically tell the maximum permissible deviation from the base levels. The only right way to tune those is with in-cylinder pressure transducers.
You can do headphones and a multiplicative addition in a pinch, but I would not touch those until you verify that the ECU is seeing knock where there is none.

Look at the KRRA module, specifically KRFKN/KRFKLN, which tells how much to retard on a single knock event, as well as KRVFN/KRLVFN/KRVFSN, which is the speed at which the ignition angle is phased back in.
You can try to reduce the amount if pulls right off the bat, but if the amount you pull is not enough the first time, and you end up pulling more the 2nd time, you will lose power. As the cylinder heats up more and more due to knocking combustion, the fuel will be more and more prone to detonation.

I have been doing extensive testing over the last week or two adjusting all of the standard knock variables including KRFKLN etc.
I've probably made about 15 tunes in the last week trying various things.
I'm always open to more information and others opinions but I do have quite a lot of experience tuning high boost engines... i've been flown across the country to help people tune... I'm not totally new at this.

I'm not sure I have any of KRVFN/KRLVFN/KRVFSN defined for the M Box though... Anyone have those locations handy?

But having said that I plan to make a detcan and use that for testing alone with a knocksense unit that I have laying around from a Megasquirt install I tore down.
I'll let you know what I find...
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britishturbo
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« Reply #74 on: January 23, 2013, 09:24:09 PM »

OK I've found all but KRLVFN now I think.
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