JB4 logging question: Target boost data unit convention

[i3igpete]

Why don't your boost targets in the log match your Map 6 settings? (shown below)

map6_15	map6_20	map6_25	map6_30	map6_35	map6_40	map6_45	map6_50	map6_55	map6_60	map6_65	map6_70
14​	14​	15.1​	19​	19​	19​	19​	19​	19​	19​	19​	19​

These won't work anyway. you need to taper boost targets on either end.

Try something like this:

map6_15	map6_20	map6_25	map6_30	map6_35	map6_40	map6_45	map6_50	map6_55	map6_60	map6_65	map6_70
13​	14​	15​	16​	17​	18​	19​	20​	20​	19​	18​	17​

Auto boost redux only needs to be changed if your gear changes aren't smooth and quick. higher number there = more boost dumped out the wastegate during upshift.

Ah, I was trying to force the jb4 to start a new log grouping by changing settings, but it wouldn't let me and kept throwing everything into the same CSV. Is there a way to do that manually? I suppose I could just delete the existing CSV.

I thought I was going nuts, the boost kept tapering no matter what I did with duty bias at the high end (that's why the bias is a crazy value at redline, something like 65). Maybe a new downpipe will help VolEff at the top end?

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[ColonelAdama]

Ah, I was trying to force the jb4 to start a new log grouping by changing settings, but it wouldn't let me and kept throwing everything into the same CSV. Is there a way to do that manually? I suppose I could just delete the existing CSV.

I thought I was going nuts, the boost kept tapering no matter what I did with duty bias at the high end (that's why the bias is a crazy value at redline, something like 65). Maybe a new downpipe will help VolEff at the top end?

It's pretty normal to need to raise Duty bias values for 5k rpm+ to get near target. That's why BMS recommends the EWG cable when running higher boost.

Adding the downpipe usually requires dropping duty bias below 4500 as well since it makes more boost than intended with stock wastegate mapping.

for reference, here are mine (catless):

duty_15	duty_20	duty_25	duty_30	duty_35	duty_40	duty_45	duty_50	duty_55	duty_60	duty_65	duty_70
38​	38​	38​	38​	41​	45​	47​	52​	54​	56​	56​	54​

I don't group logs because I'm constantly changing my map 6 settings, and I want to know the exact setting used for the run in the log.

 

[i3igpete]

Hahha, my roots are Apexi S-AFC's on DSMs, I know this all too well.

What I would give for just a single-knob mechanical boost controller right about now...

were you around for the days of using a crappy palm pilot to log knock and timing? I remember my buddy coughed up the money for a scan master and it was like he was living in the future. don't miss that part ...

 

[ColonelAdama]

What I would give for just a single-knob mechanical boost controller right about now...

Should have just bought a JB+ then

not really though

 

[i3igpete]

Try something like this:

After your suggestion i looked more closely at my logs on my desktop. I now see the turbo is only capable of generating 15 psi at 3000 during my 4th gear pulls. that request of 18/19 psi at 3000 is probably contributing some wonky behavior too.

Using the upper-bound of this 5-pull scatter plot, I wonder if something like this would minimize PID windup.

map6_15	map6_20	map6_25	map6_30
4	8	16	17

 

[ColonelAdama]

After your suggestion i looked more closely at my logs on my desktop. I now see the turbo is only capable of generating 15 psi at 3000 during my 4th gear pulls. that request of 18/19 psi at 3000 is probably contributing some wonky behavior too.

Using the upper-bound of this 5-pull scatter plot, I wonder if something like this would minimize PID windup.

map6_15	map6_20	map6_25	map6_30
4	8	16	17

I honestly don't pay much attention to any of the values below 3000 since you should rarely go WOT there anyway. I would recommend just putting whatever DME_BT reads for any RPM below 3000 to run stock targets. To make it a passthrough basically. Your log suggests that value is about 14-15 psi.

And just for future reference, no point in starting logs before 2500. Nothing to learn about your map below the boost threshold.

 

[i3igpete]

And just for future reference, no point in starting logs before 2500. Nothing to learn about your map below the boost threshold.

true, but with a quick spooling turbo like this, it seems the control logic and transients have a significant effect. I figure if I start below boost threshold, it would at least knock out pedal-related variables.

On a related note, I overlaid a 3rd gear pull from another user running map 2, and it showed a boost threshold right-shifted by ~1000rpm. I certainly didn't expect that. How much of that is due to JB4 logic vs gearing, not sure - but interesting to see. Going to try and paste a couple more in and find a pattern.

https://www.supramkv.com/threads/jb4-hitting-25-7-psi.13613/

 

[ColonelAdama]

true, but with a quick spooling turbo like this, it seems the control logic and transients have a significant effect. i overlayed a 3rd gear pull from another user running map 2, and it showed a boost threshold right-shifted 1000rpm. i certainly didn't expect that.

Hm, well let us know what you find out. I feel like if you set the targets to what you said, you may just introduce some throttle closures on spool up. Who knows!

 

[i3igpete]

Merged a bunch of logs from here as well as jb4 forums. Boost thresholds seem to be +/-500 rpm even though everyone seems to be using 3rd and has an automatic (2 quick upshifts upon lift gives it away). I'm guessing it's probably software-related rather than gearing, assuming zf8's aren't drastically different from car to car.

One fellow with an m340 (yellow dots) found out that in 2nd gear the engine outruns the turbo and it doesn't spool up until 4500. But on the other hand, it looks like his transient had a maximum spoolup time of about ~5 timesteps from 5psi to max boost.

 

[razorlab]

What I would give for just a single-knob mechanical boost controller right about now...

were you around for the days of using a crappy palm pilot to log knock and timing? I remember my buddy coughed up the money for a scan master and it was like he was living in the future. don't miss that part ...

I still have my palm pilot with the logging software. lmao.

 

[i3igpete]

I would recommend just putting whatever DME_BT reads for any RPM below 3000 to run stock targets. To make it a passthrough basically.

Ah, good call. Thought about it a bit and the DME might freak out if the JB4 sends back a massive vacuum signal.

 

[ColonelAdama]

Merged a bunch of logs from here as well as jb4 forums. Boost thresholds seem to be +/-500 rpm even though everyone seems to be using 3rd and has an automatic (2 quick upshifts upon lift gives it away). I'm guessing it's probably software-related rather than gearing, assuming zf8's aren't drastically different from car to car.

One fellow with an m340 (yellow dots) found out that in 2nd gear the engine outruns the turbo and it doesn't spool up until 4500. But on the other hand, it looks like his transient had a maximum spoolup time of about ~5 timesteps from 5psi to max boost.

Pretty fascinating scatterplot. Thanks for sharing.

 

[i3igpete]

Adding the downpipe usually requires dropping duty bias below 4500 as well since it makes more boost than intended with stock wastegate mapping.

So to follow up on this, the downpipe had very little effect on top end VolEff, so the cylinder head or hotside appears to be the bottleneck there. However, the JB4 got quite confused on that first drive. Out of curiosity, I ran map 1 with default duty bias table, and still no go. The ECU was hunting with the throttle, even after a few pulls to auto-tune the WG adaption.

Anywho, duty bias had to be turned down quite a bit in the low and midrange. Adam and I went back and forth a bit, and here's the delta in duty bias that we settled on until I have time to get some more logs. (Note that the logs posted earlier is NOT the baseline for this delta.)

1500​

2000​

2500​

3000​

3500​

4000​

4500​

5000​

5500​

6000​

6500​

7000​

Duty Bias delta

-6​

-6​

-8​

-10​

-12​

-12​

-8​

-4​

-6​

-2​

-1​

-1​

We also smoothed and tapered the boost curve slightly, but still within ~1 psi or so.

This is purely to illustrate that a downpipe will necessitate a drop in duty bias by 5-10 across the midrange.

 

[ColonelAdama]

So to follow up on this, the downpipe had very little effect on top end VolEff, so the cylinder head or hotside appears to be the bottleneck there. However, the JB4 got quite confused on that first drive. Out of curiosity, I ran map 1 with default duty bias table, and still no go. The ECU was hunting with the throttle, even after a few pulls to auto-tune the WG adaption.

Anywho, duty bias had to be turned down quite a bit in the low and midrange. Adam and I went back and forth a bit, and here's the delta in duty bias that we settled on until I have time to get some more logs. (Note that the logs posted earlier is NOT the baseline for this delta.)

1500​

2000​

2500​

3000​

3500​

4000​

4500​

5000​

5500​

6000​

6500​

7000​

Duty Bias delta

-6​

-6​

-8​

-10​

-12​

-12​

-8​

-4​

-6​

-2​

-1​

-1​

We also smoothed and tapered the boost curve slightly, but still within ~1 psi or so.

This is purely to illustrate that a downpipe will necessitate a drop in duty bias by 5-10 across the midrange.

Glad you were able to do this comparison. I never had JB4 with stock downpipe to test.

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