8) usually spark knock happens at low rpm under load when cylinder pressures and heat are at their highest. when you get a spark knock at higher rpms, you have what is known as preignition. they sound about the same, and have the same end result, engine damage if left unchecked, but they have different causes. detonation is usually caused by higher cylinder pressures and the extra heat that results from those higher pressures. this can also cause a hot spot in the normal carbon build up on the pistons to glow, but not cause a preignition condition until the cylinder pressures rise to a high enough point to allow it.
high rpm preignition is usually caused by a plug that is too high of a heat range for the engine. what happens is that the high heat range plugs retain heat, and the tip will glow hot enough to light the fuel mixture prematurely. sometimes it can get real bad and light the mixture off as soon as it enters the cylinder causing a high rpm backfire(ever see a blower pop off a top fuel motor at the track? that is severe preignition.). in your case i suggest trying a plug one heat range colder, or use an extended nose plug as that will allow the incoming fuel mixture to cool the plug without lighting off.
