Torque Management Advance – one more source slain?

For today’s test I increased the pressure delta. One test (pictured) had no TMA at all (yay)

Boost comes right up, and torque is pretty flat. Cooler day, so almost SAE1349 conditions with a small correction factor of 0.2%.

The other test sample for today does show some TMA.

The rate of increase may be addressed now, but I note that the new TMA happens when Cylinder airmass exceeds 1.32. More study is needed; that is below the current tune knock airmass table. I suspect this is a 3rd source of TMA however.

This chart compares total cylinder airmass with boost and TMA

Cyl Airmass to Boost to TMA

Torque Management Advance to Pressure Delta

I have made progress in reducing the torque management advance (TMA) by RPM Limit Accel Thresh vs. Accel. However, there is still some TMA remaining. I suspect there were multiple sources for the TMA — we solved one. My next hypothesis is that there is some torque management advance coming from boost rate of increase exceeding the allowed pressure delta.

I see in the prior graphs that when there is torque management advance there is also rapid boost increase. I assumed that this was due to the TMA, but it got me wondering if the rapid boost increase was actually a causal factor for the TMA.

I am not clear how Cadillac calculates rate of boost increase. To try to model the rate, in the graph above I first graphed the limit in blue. Then I considered a rate of increase per 0.1 seconds from my log 1E. In other words, what was the % of increase in boost over 0.1 seconds? I graphed that in red. Finally, where do we see TMA on the same run? I graphed that in gray. I can see that the TMA correlates with the boost increase rate. Correlation does not equate to causation, but it is a clue.

My next test will be to increase the Pressure Delta Factor to determine if that has an impact on torque management advance.

Less Torque Management Advance is better Torque Management Advance

This tune had a couple of fixes to try to eliminate the torque management advance. They were partially successful.

Previous run showed two spikes with up to 12 degrees of torque management advance; this run had one spike with only 4.2 degrees. Although there is still some TMA, this was progress.

I have been showing the graphs as xy graphs, hp to rpm for example, which is the way a dyno might show similar data. However, this does not consider the time aspect — it takes much less time for the engine to get to 4500 rpm than from 4500 to 6500 for example.

This shows time offset from hptuners scan along the X axis instead of RPM. My impression is that they are time in seconds of the scan. It is time correct, and RPM builds from left to right but I have not discerned a best way to show both the HP vs RPM and HP vs TIME on one chart yet.

This second chart is useful however for understanding when events occur in time — go WOT, tip-in and boost, torque, and RPM build rapidly. A largely flat torque curve that matches the boost curve.

The remaining TMA retard appears to coincide with rapid boost development. My next test will be to see if that is a limiter.