This was going to be my next point - I guess the suggested heat range was wrong for your set-up? Cos surely you get a plug that'll draw the heat away from the tip better? (colder range) preventing it from breaking up?
Cheers for the info - I'll keep that up my sleeve for the next time anyone is raving about them over another brand.
P.S. ShaunyBoy - Have a search for Flame Propagation/ Flame front in internal cumbustion engines. There's much information and many studies into exactly how flames propagate from the spark plug! and how this affects performance!
for sure, the IK22's I used did not suit the spec.. my bad, and @ my cost
Denso's tech help, and refusal to guarantee the plug they spec'd for my actual spec however is what nailed it to NGK tho. If they cant guarantee their product but advise it, its time to walk away.
Since heard of several IK22 users suffer failures.
No performance drop, and blissfully unaware the ceramics had indeed fallen apart inside the engine. Only as a consequence of the headgasket going and me needing to remove the head, did the damage reveal itself.