Asking for a friend… What happens if a high-performance engine, modified or tuned for unleaded avgas like G100UL or UL94, suddenly has to run on 100LL again? Could this lead to detonation issues, increased lead deposits, or unexpected maintenance problems? With unleaded avgas burning cleaner and some engines being adjusted with advanced timing or mixture settings, I wonder if reverting to 100LL could pose safety risks or damage critical engine components. If so, how should pilots, mechanics, and aircraft owners prepare for this possibility?