[DeaneG]

I went ahead and installed eight Denso Iridium spark plugs in my car last night, replacing the stock NGK's with 6000 miles on them.

Anyway, in my car, they made absolutely no difference over the stock NGK's in any way I could detect. I was hoping they'd help clean up a little tremble at idle because of their slightly wider gap, but that didn't change at all.

I thought the NGK's center electrode construction looked better, a tapered pin rather than a straight wire.

I was surprised how clean the old NGK's looked, like they could go another 20K miles or more.

 

[DeaneG]

That's what I think - cars that experienced noticeable performance improvement with Denso plugs probably just needed new plugs.

It's hard to imagine that Denso would keep secret a real performance advantage from engineers at Ferrari, etc.