Being pointed by admin to this thread, all I can point to is that you've been running the FRS engine without a recirculating valve, standard or uprated, nor a basic twin piston dump valve. To get the chatter you did in those videos you posted, I'm assuming you've been nailing it around quite a bit with those key parts all blanked up. Wasn't a good idea seeing as how its a pretty tempremental engine anyway.

Basically, it runs temps of around 96C-101C before the fan kicks in, the first plug you killed (which really should have been Denso's and not crappy NGK's) was probably due to overheating