The SC is increasing compression, and with increased compression you are seeing detonation aka pinging. Diesels use high compression to cause the fuel to detonate as soon as it is injected, you are injecting fuel with the intake stroke, and using the spark plugs to light it. The pinging is the fuel lighting up before the spark fires, as in before it is suposto. The fuel is burning & causing the pressure in the cylinder to climb before it is at top dead center (tdc). This makes the crankshaft push the piston up into high pressure expanding gasses.. If it pings to earily, and at a high enough throttle, you can bend the connecting rods between the piston & crank.. then you get a new engine, as the crank is usually damaged, the piston moves farther down then it is designed to, and the bent rod can / will contact the inside of the bore, putting shavings in the oil, and dropping them on everthing, destroying the oilpump, which will cause you to loose all oil pressure in a few seconds, let alone the giant dent in the side of the bore itself.