Originally Posted by mecinoid

Well a lot of cars mfgs. will tell you that you don't have to replace your spark plugs until 100K. However, I replaced my stock Platinum spark plugs with NGK Iradiums about 6 years ago now and what a difference. Them darn things are $6 however. The car ran a lot smoother and I ran slightly better times at the track. I figure $50 for better plugs and smoother idle was worth it alone.

I figure I'll replace my spark plugs with Iradiums in my 350Z now. I just forgot how nice a improvement it was on my Firebird. Now that this has been brought up I'll change them in the next couple of days and see if I notice a improvement. I'll post back here if I get a chance to do this.
Below is the info I found on the NGK site.

NGK IRADIUMS = Iridium IX LFR5AIX-11 gap at .044

The Spark Plug Serious Enthusiasts Rely On

Iridium IX Spark Plugs are the most technologically advanced high performance plugs available. Featuring a 0.6 mm iridium center electrode tip, they offer superior ignitability without sacrificing durability. The tapered ground electrode increases flame kernel expansion, while the superior heat range design is ideally suited to the demands of high performance environments. Specially designed to meet the needs of serious enthusiasts, Iridium IX Spark Plugs offer outstanding acceleration, high fuel efficiency and long life. When you demand the most from your engine, rely on the proven performance of NGK Iridium IX Spark Plugs.

NGK's new Iridium IX is the personification of these qualities and takes premium performance spark plugs to a new level. A level that is expected from the world leader in spark plugs.

The future has never looked so good.