In the last month I have gone through about 50 more tunes trying to sort the issue of controlling the boost with the throttle while the boost pressure is under the waste gate cracking pressure. I have had limited success.

WOT is great, car is fast and runs as expected. Less than 50% throttle up to 7,000rpm is good. It isn't "butter smooth", but it is fairly smooth and totally reasonable to daily drive. It is 60%-80% throttle at above 4,000rpm where everything goes wrong and I get the horrible "kangaroo-ing" throttle/boost.

Kangaroo-ing -> https://drive.google.com/open?id=1E6USTu7CwxQg5MGBVDAwTqEszm3N8jLZ

KFVPDKSD ->https://drive.google.com/open?id=11qR5cZURsyw3TWhiqz-ZQUMmJZqiKZEX

WDKUGDN -> https://drive.google.com/open?id=19HPbVIqw8H-5UvlYQh5WQTAlIFI9JiVe

KFVPDKSD/E

I agree with prj that the only rational way to define this map is by taking logs at 0% WGDC and 100% throttle to see where you need to close the throttle to control the boost (i.e, requested pressure ratio can be achieved and exceeded at a given RPM) and where the throttle should be 100% open (i.e, requested pressure ratio cannot be achieved at a given RPM). This map is fairly trivial to rough in, much more difficult to fine tune when you consider what WDKUGDN has to look like.

One of the issues I ran across was that I have these logs in 30 degree F ambient temperatures and 90 degree F ambient temperatures an there is a big difference in what pressure ratios can be achieved for a given RPM. The difference between 30 degrees and 90 degrees might be a pressure ratio that varies as much as 0.5 for the same given RPM and that can shift you a few columns to the left or right in KFVPDKSD/E. I opted to take the most aggressive logs (cold weather) and use those. Worst case is I am over throttled in hot weather.

WDKUGDN

To actually control the boost with the throttle (especially at high RPM) WDKUGDN has to close down the throttle aggressively. A throttle position of somewhere between 16-22% seems to be the sweet spot. Closing the throttle more than 16% seems to put the engine close enough to vacuum that the DV's will release in a rapid cycling manner, or maybe it is a surging issue...  However, even at 20% you will see the boost creep up as the RPMs increase.

Log -> https://drive.google.com/open?id=1QREWRBu_SXp0FObmGIPpV1okiY_K9lXM.

Because the difference between WDKUGDN and the requested throttle angle at a high throttle/high rpm is so large, even a small change in the Z-values in KFVPDKSD/E have a huge effect on the throttle angle. Another issue I see is that the MAP sensor is upstream of the throttle body and the compressor wheels of the Tial's 770's can have a lot of angular momentum. This means a big change in throttle position at high rpm can cause a big pressure wave back upstream towards the turbos. The result is pvdkds spikes (MAP is pre-throttle body) but the pressure in the intake manifold can drop to near vacuum which causes the DV's to dump followed by a series neck snapping kangaroos. Also, this can't be good for the turbos.

The Point:

I have basically exhausted every reasonable set of values for KFVPDKSD/E and WDKUGDN. Because of the differences in PR for ambient temperatures, the low resolution of the maps, the basically infinite number of ways a pair of X and Y values can be interpolated for in the maps, the transience of the turbos, the pre-throttle body MAP and the throttle angle required to control boost at high RPM... it is extremely difficult (maybe impossible) to get this right. I know others have claimed they have nailed this with similar setups, I am skeptical.

The Future:

I think prj is onto something with inverted DV's and the DV's needing to dump excess boost. I have seen AMD cars with inverted DV's and wondered for a long time what the reasoning behind them was. It would be reasonable to assume the issues I have been seeing are why the DV's have been inverted. So, next step is to try that. Feel free to explain why I am totally wrong and everyone else has "butter smooth" big turbos.

Update: First try with inverted Forge DV's with a stiff spring is a failure. I can't get over 2-3psi of boost. Obviously a big pressure differential, I am thinking I can't get the engine completely out of vacuum, but I'll trouble shoot and give it another go if I can find something wrong.

Thanks, Nye. Unfortunately, at this point I can go on and on about what hasn't worked and all of the many reasons why it probably didn't work, but I don't have much to say on what has worked or ideas I have left that might make it work.

K03's have a low cracking pressure, they spool very fast and they have a relatively small amount of angular momentum. That is to say with K03's, you don't spend much time in areas of KFVPDKSD where vpsspls_w << 1 and even if it is, the K03's are more responsive to throttle inputs and overall it is more of a 'smoothing' effect rather than an outright 'control' effect. That is to say, I am fairly confident the throttle control was never intended to be used as full form boost control.

At this point I would take moderately smooth even if the throttle/power delivery is very non-linear at high RPM's (just no kangaroo-ing), but that is going to take some serious tweaking to the load maps to get requested load up to the point that the turbos are going to make and I just have to deal with not having full control over (which takes me back to the original point of this post after all of that...).

There is no desired vs. actual boost in this last log, but to me it looks like over-boost throttle interventions, I see them on my stock ME7.9.10 setup from time to time. So perhaps a separate issue from WDKUGDN / KFVPDKS tuning?

Another thing - on the mentioned ECU of mine there is no WDKUGDN (well, there is, but it is turned off with a code word), and the values are calculated from KFWDKMSNVP. If anything, this tells me that these two have to stay in close relation for the whole thing to work. So perhaps it is unwise to touch WDKUGDN as long as the throttle body is stock?

Edit: not untouched but checked to be in sync with the other one.
 

I tried this approach. I think it gave me the "smoothest" results so far, but the actual boost was much higher than desired and I went back to closing the throttle more aggressively to keep actual boost more in-line with desired. The other option would be to raise KFMIRL in areas above 4,000rpm/50% throttle to something that better resembles the boost I see when MSHFM ~= MSDK , but I haven't had great results with that so far because of the mysterious torque interventions.

v101 - MSHFM vs MSDK -> https://drive.google.com/open?id=1HbIspqY1jUT7qpWPuegWl0awcIYoxUMo
v101 - PVDKS vs PLSOL -> https://drive.google.com/open?id=1nM08ceuV2m_PBBN8Rh5ZiWq63VGGrXIo
v101 - Logs -> https://drive.google.com/open?id=1_xrOgcrv_61DFtuPHSkNuiAAdEsS3XPK

The approach where I try to keep the throttle angle small to keep PVDKS != PLSOL results in MSDK << MSHFM.

v121 - MSHFM vs MSDK -> https://drive.google.com/open?id=17wzhhWmbcH6GUpT1IhP5iu-i_dKmRH8o

It is odd that msdk is increasing while the throttle angle is decreasing. Modifying KFWDKMSN/WDK to get MSHFM ~= MSDK might help fix the throttle cuts, but that seems questionable.


v121 - PVDKS vs PLSOL -> https://drive.google.com/open?id=1rNogbvzKOQw0dSLqdGnE0hcHT2N8jMPS
v121 - Logs -> https://drive.google.com/open?id=1ZtC6FUZCcMWlrIANaQlxHNTeWONrayGm

So yes, it looks like over-boost throttle interventions could be the cause (although I thought I had disabled them). I think decreasing WDKUGDN above 4000rpm to prevent overboost and trying to get KFWDKMSN/WDK to output something more reasonable for msdk are the next steps to take. Maybe increase KFMIRL in places I can without hitting the mysterious torque interventions.

This is my understanding of it as well, but it is not what I am experiencing. I still see overboost codes, throttle cut, etc.. presumably because of pvdk since ps_w is always less than pssol_w. What am I missing here?


To be clear, my DV springs are comparable to what is in the 710P. I have inverted them as you suggested and I couldn't make any boost, even with the most stiff springs in the DV's. I see no reason that 710P would perform any better in this orientation.

In general I agree with what you are saying, I am just not seeing good results when I take that approach. Could you provide some logs from a BT car so I can see your approach to ps_w vs pssol_w and pvdks vs plsol?

It is by ~25%. It would be right at the limit if it were not.

And here's the problem. DUH. What limit are you on about?

Overboost codes specifically can be removed by adjusting KFDLULS.
Throttle doesn't give a damn about your boost, it's only about manifold filling.

Tune the ECU like the FR says and you won't have issues. Rather than "scaling this" "scaling that" "doing this" "doing that" - of course when you screw up all the models your throttle control goes nuts, what do you expect?

Also I've not had issues making boost with DV's inverted. Maybe something is not fitted right?