I posted below on the issues I am having tuning a customer's 2010 GT500, with VMP 2.3 supercharger. We had it on the dyno again today, and I have more data to report on the problem. We made three WOT pulls on the dyno. None was as good as the clean WOT runs we'd seen with this car before, and each successive run was worse. Looking at the logs (attached), what stands out is that the timing gets dramatically lower with each successive run. By the third run, we're down to 6 degrees max!
The engine had at least 5 min to cool between each run, and the IAT and ECT are very close between them. Looking at the timing logs, the timing plots look quite smooth, just very low. The timing plunges to a low level as soon as the throttle is floored, and stays down the whole way up. It's as though the ECU is "learning" from run to run, and pulling more timing each time, kind of like a GM low-octane/high-octane learning.
I think the power issues are pretty much strictly timing related. The MAF voltage vs. RPM is very similar through all 3 pulls, which would tend to eliminate belt slippage or ETC issues.
I've attached a JPEG of three dyno pulls: a clean high power run, and the last two low power pulls from today. I've also attached the current tune file, a log from a clean pull, the 3 logs from today's sessions, and the config file.
If somebody could make some suggestions, I'd be grateful. The time and frustration are mounting up!
Edit: One oddity I noted is that the Barometric pressure varies as much as 9 KPA between (and within) the pulls?