Ailing engine (Updated after teardown)

Food for thought... My daily driver 2000 Buick has the 3.8L V-6 with an Eaton M-90 Roots supercharger from the factory. It has a pretty sophisticated (for the late '90s) ignition timing control and knock sensor system. The knock sensors can tell the severity of detonation and the computer will retard the timing accordingly then slowly (over the course of a few seconds) advance the timing back to the base value spec'd in the tuning map. I have a connector and tuning software on my laptop for that car. I've run live data scans monitoring the knock retard and total timing advance and when first getting into boost (around 1/3 throttle) it gets momentary knock and I've seen it retard the timing as much as 12°. Never once have I ever actually heard pinging from the engine, and it's a very quiet engine with stock exhaust so I would hear it if it was there.

The max advance I can run under WOT before the knock retard pulls timing back out is only about 18°, granted it's a smaller-bore engine than a 360 SBM but still. That engine has 8.5:1 compression and runs 6 psi of boost, ramping up to 8 psi from about 5000-5800 RPM as the airflow efficiency of the engine goes down. Running 93-octane premium gas too.