Usually performance plugs last "around 30k". The Denso Long Life is the one that last 100k.

 

you guys belive what you want but gaining 5hp from a plug on Naturally aspirated bone stock v8 is just bogus, in teh time the guy dynoed his car and changed plugs alot could of happend. I've seen alot of time when the engine temps are down 20 degrees and you get a few hp more, or the air ges cooler/less humid. Theres just too many things that can cause a dyno to read slightly higher, i would def not count that these plugs give more power, if so the engine would run leaner. My SC plugs were original BTW with 180k miles along with plugs,wires,cap and rotor when i bought the car. I did the work to the car not because it ran bad(it ran great) but because i had to remove the intake manifold to change leaking valve cover gaskets and i was right there so i just did them.