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.

Traction off, Torque Management Continues

Scan D5B

Today’s scan was with traction control disabled, to determine if the Torque Management Advance (retard) (TMAR) was originating from TCS. I observe that we still have TMAR with us, so I conclude it is not, and further study will be required.

Comparing today’s D5SB with prior D5SA, today’s peak was 468.9 whp vs prior peak 476.8 whp, or 8 less. Prior was a warmer day with somewhat higher humidity and earned a larger dyno correction of 2.4% vs 1% today. I am looking for repeatability here, and under 2% may be par for this type of testing.

I have added relative humidity to my scan table, so that the resulting scans can be self-correcting for conditions via dyno correction factor. The car tracks barometric pressure, relative humidity, and ambient temperature. With those figures an SAE 1349 dyno correction can be applied, and is figured in prior to graphing. I am also using a 400/464 ratio here for crank to wheels; I find this matches precisely with stock results.

Stock vs GM Dyno

This graph takes the GM LF4 engine dyno, converts it to wheel torque/hp, and compares it (dotted lines) to a scan from a stock ATS-V also converted to wheel hp (solid lines). They appear to overlay nicely.