Originally Posted by Brian Carlton

Just so you fellows are aware, an engine can have what we would call "spark knock" and be just fine with it. When I worked for Chrysler, they would deliberately let an engine knock for many thousands of miles and there is no detriment to the engine in any way.

The generally accepted theory that spark knock will cause damage to an engine is false. You can use regular gas in an engine designed for premium and it might knock a bit, but will never damage itself.

To proceed to damage requires significantly more timing advance or lower grade fuel until true detonation occurs and damages the piston tops.

The main reason that the manufacturers don't want the engine to knock is that fuel economy drops off as soon as this occurs. Some of the fuel is not burning at a proper rate in the cylinder.