How to calculate overboost on map 3

[StingerScott]

When looking for over boost in a log, am I adding the ecu psi(say 13), and target(6.0) and then aligning it with the actual boost I had like in the log I attached? Or am I way off, is this log ok in that sense? Thnx

 

[StingerScott]

here is what I found if anyone new to this is wondering how to calculate overboost,

1. Look at “ECU_PSI” (real boost) in your log.

2. Find “DME_BT” (target boost) for the same RPM.

3. If ECU_PSI is more than 2 psi above DME_BT, it’s overboost.


Example: If DME_BT is 17 psi and ECU_PSI is 20 psi, that’s 3 psi over—overboost.

 

[Plakchup]

Very handy thanks for sharing.

I was looking at my recent log with the wastegate adaptations to near 50 and it looks like its about 1-1.2 psi difference at most and it gets real close as revs go higher.

Gets closer when i bring the adaptations to about 45 or even 48. Was curious to see how the car was after the bms chargepipes were installed with the bms intercooler. Car definitely liked it!

 

[Thomby]

1. Look at “ECU_PSI” (real boost) in your log.
2. Find “DME_BT” (target boost) for the same RPM.
3. If ECU_PSI is more than 2 psi above DME_BT, it’s overboost.

I don't think this is right, have you run this by Terry or the BMS forums? My understanding is:
- ECU_PSI is what the Stinger's (stock) computer wants
- DME_BT is not relevant as the DME is a BMW-specific computer (unless this value has been repurposed)
- Boost (and Boost2) are what's present in front of (and behind) the throttle plate...should basically match at WOT
So if you want to compare what's the JB4 wants to what's physically happening, you should compare ECU_PSI + Target to Boost/Boost2.

Here's the BMS link to Stinger-specific parameters. It's from 2019, so it's possible things have changed:

JB4 Logging Parameters - JB4tech.com - International Turbo Tuning Discussion

Hey guys, We’ll use this thread for details and discussions on Kia specific JB4 logging parameters. Fuel trims and wideband o2 sensor control explained here...

www.jb4tech.com

DME_BT: This would represent how much boost the ECU is requesting at an given moment but is not enabled on the Kia platform yet. Instead we use an internal algorithm to estimate what the factory boost target should be.

 

[Plakchup]

From what I've gathered and unless I am mistaken, if you see a too high of a WGDC spike and sudden drop in boost as the rpms are climbing, then that's considered overboost. So I guess ideally you want less of an WGDC spike and smooth boost curve, and HPFP not going below 10.

 

[Thomby]

if you see a too high of a WGDC spike and sudden drop in boost as the rpms are climbing, then that's considered overboost

WGDC as displayed in JB4 logs is not the duty cycle itself (ie how closed or open the WG is), but the scaling the JB4 is applying to the stock signal. 50 means it's just passing the ECU's signal unmodified, and a higher number means it's scaling up the stock signal to build boost faster.

So in an overboost scenario, I would expect to see the WGDC drop well below 50, scaling back the signal the car is sending, to open the WGs further/faster. And a WGDC spike would be the JB4 seeing that actual boost is lagging requested boost, and telling the WGs to close more than the stock ECU wants.

(If you don't have EWG connectors, I think the value is just what the JB4 wants to do, given boost target and actual boost.)

 

[Plakchup]

Appreciate the explanation. I have the ewg wires and they are really awesome. So when you lower the wastegate adaptations number, does that mean the jb4 is modifying the wastegates signal to open more and faster?

Can't wait do the BEF soon once January comes around. Probably wil leave the ewg wires hooked up but disabled in jb4 since the bef will handle it better. I believe same applies to the fuel wires which i am using the adapters for. No need to disconnect them I assume.

 

[Thomby]

So when you lower the wastegate adaptations number, does that mean the jb4 is modifying the wastegates signal to open more and faster?

The first time I read through the explanation of the settings, I didn't fully follow it, but I think FF (Feed Forward) controls the initial duty cycle as the car attempts to make requested boost, and the PID value is how much it can stray from that base value.

So bumping FF up or down is the recommended way to change overall wastegate movement, and I think PID Gain changes would be for second order issues, like boost surge/oscillation. An FF decrease should reduce your starting point, before the closed loop PID logic kicks in, so less closed wastegate, less responsive, and less likely to overboost. I think.

Probably wil leave the ewg wires hooked up but disabled in jb4 since the bef will handle it better. I believe same applies to the fuel wires which i am using the adapters for

If the flash remaps the duty cycle the computer calls for, that should make EWG scaling by the JB4 less important. And if it also leans out up top, you wouldn't need the JB4 to manipulate the AFR value going to the ECU.

But I don't remember changing any settings when I installed my O2 wires, so it may just always try to adjust regardless of whether they're connected. I'm not sure how it would react on top of a flashed ECU...maybe the JB4 would just see AFR where it wants it, and not try to provide any adjustment.

 

[Plakchup]

Great information! I guess I will find out soon around january once I do the BEF with KJT E30 tune and BMS TCU tune. Luckily I live pretty close by BMS and cmbuildz who will set it up for me so it will be a fun learning curve. I think I remember him (cmbuildz) telling me that I will not need the ewg and fuel wires anymore once we go BEF. Pretty excited to see the difference especially for the TCU since I sometimes really hate it's shifting behavior. From the very positive feedback I've received from those running KJT BEF and BMS TCU tune it should make a nice difference from just running JB4 on it's own.