The S55 crankshaft hub (harmonic balancer) is a press-fit design that can slip under high load, losing timing correlation between the crank and cam. More common on tracked or tuned cars. When it slips, the engine can jump timing and bend valves.
Symptoms
Sudden loss of timing, rough running, check engine light, metallic debris in oil pan. Often occurs during high-RPM events.
Fix / Remedy
Preventive crank hub pin/key upgrade kits available (IRP, VAC Motorsports). Requires engine removal. Pins the hub to the crank so it physically cannot slip.