Predetonation can be initiated in a number of ways.
The easiest is have the whole stratified charge too lean and having the charge explode before it's time.
Next, you can push a properly rich charge too fast and excite it too hard (too little squish clearance and/or compression too high for the given fuel quality) causing the properly rich and stratified charge to explode prematurely due to heat and friction.
Third, you can overheat the engine causing a properly rich charge to de-stratify so there are lean pockets near the cylinder wall which can explode prematurely.
Fourth, you can have carbon build-up or cylinder head damage which can become a "hot-spot" causing a properly rich and stratified charge to ignite using the "hot-spot" as the ignition source before the spark plug fires.
If you have a little carbon build-up and an airleak combined, at lower temperatures (not WOT for a few seconds) the carbon isn't hot enough to ignite the slightly lean charge. Once the engine is run hard for a few seconds (1st thru 3rd perhaps) the carbon gets hot enough to ignite the lean charge.
