There's much more to a plug than meet's the eye's as I have learned!
You are correct the plugs job is mainly to deliver spark but you think a Top Racer would spend $130 for one Denso Plug if it didn't matter. The truth is it does. The Core, Heat Range, Electrode and Ground Electrode all play a major factor in optimizing the efficiency of an ignition system. Realize this when referring to Denso, spark plugs is like a tax write off for them really when you consider all the more advanced products they provide for nearly all Car Manufacters that circle this Globe! Fortunately Denso didn't just design another Plug, they advanced the Technology from the Core, the .4mm Electrode, the patented Tapered Ground Electrode and U-Groove plus there 5rib design. I hate to make these plugs seem like heavansent, but I will say that when it comes to Iridium, Denso TOP's!!!
I will vouch for the Performance Difference I have seen including a major KICK in the A*S at about 5500rpm that I never felt previously with the Autolites.
