Cadillac XLR LH2 Tuning – Tune 6D Better is not always better

Today’s test Tune 6D was to keep the early VVT changes from Tune 6C with some late changes back from Tune 6B.

I have also slightly modified my Virtual Dyno settings.  Virtual Dyno uses barometer and intake temperature inputs to correct to an SAE standard.  Each test run captures the local baro and intake temps as the XLR sees them, but they tend to vary slightly across the run.  The new change is to take a mathematical average of the baro and intake temps for each run and use that average value in the Virtual Dyno for that run.  Previously I had settled on a fixed 29.83 for baro and did a simple 2-point average of the intake temp at the beginning of the run and the intake temp at the end of the run.

I have restated 6B, 6C, and 6D in the graph below with the new methodology:

XLR 6D comparison to 6B and 6C


This graph is only today’s test and the 6B test:

XLR Tune 6D and compare to 6B

Although 6D kept the earlier 4800 RPM VVT changes from 6C and the 5200+ RPM changes from 6B, it also had some lower advance around 5200 based on KR (knock retard) from the 6B run and some clean up and corrections.  I am not sure if the KR on that run needed less timing in the file or was unique to that run.  Another solution would be to go a little richer at that point, which is what I will try on follow-up if the next baselines show the same KR.

Next I plan to return to a duplicated of Tune 6B, (as Tune 6E), reset the baseline, and then modify from there.


I have re-visited all of my tune logs, and I suspect that the adjustments to the MAF in Tune 4 were good outside of WOT, but not in the WOT range.  I have extrapolated from the pre-WOT range to correct the WOT range of frequencies.  This would have effected everything from Tune 4 (right after Volant install) to now.

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