basic common sense......and a ton of horror stories.
Copper is a soft metal....and will burn in combustion.
Platinum is a precious metal and resistant to wear....
Iridium is even harder than platinum and resistant to wear...
The big question is......when you run into detonation....and you will, somehow one day,.....
Which spark plug....if detonated on excessively...would cause cylinder and even turbo damage?
Either the Platinum or Iridium......because the copper would burn up in the combustion as it left the cylinder.
Plus COPPER plugs are cheaper.....which means you can change them out, for less, anytime.
:farao:
* My recommendation for SBM and Boost is NGK - BPR7ES, BPR8ES, or BPR9ES......you'll find the sweet one with trial/boost level.
A stock 318/340 with 8.5:1, NGK recommended plug is a GR4 or GR5......