I have seen 3 instances where a Bosch Platinum plug porcelain insulator has broken dropping bits of porcelain into the cylinder. All three were engines that had an internal coolant leak, bad head gasket etc. I figured the larger porcelain of the platinum plug couldn't stand the thermal shock. All three also had pretty severe scoring of the cylinder walls in the effected cylinders.
I have seen 4 electrode plugs firing on test fixtures and it's true that if the spark will jump from one electrode to another in a random pattern but my impression was that the reason they developed them was to be able to get 100,000 miles out of a set of plugs.The center electrode wears in 4 spots as opposed to just one.
Back in the seventies I used to race 250cc open Mod snowmobiles. We ran a ton of oil through the engines at 13,000RPM so we were a good test bed for new plug development. I did a dyno sessions with a spark plug company testing many electrode designs and we found the best electrode for power was the tried and true symetrical single electrode. The feeling was that multi electrode plugs had too much in the way of the flame front and actually contributed to an incomplete or uneven burn of fuel. It a fairly common racing trick to index the spark plugs so the ground electrode is as close to the cylinder wall as possible to keep it out of the flame path.
If anyone likes Champion resistor plugs I suggest measuring the resistance from the terminal nut to bottom of the center electrode of a new set and one that has been run awhile. Usually around 8,000 ohms new and I have seen 30,000 to 50,000 ohms on plugs with miles on them. They drop a resistor "Pill" between the terminal nut and the center electrode with no actual connection and over time the resistance builds.
