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Discussion Starter #1
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.
 

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Actually, I felt a very smooth power delivery with the new Densos. I could feel a tad bit more torque and top end power too.

I was also surprised about the cleanliness of the NGKs... The threads were "lubricated" with a dirty liquid... but the plug itself was very clean.
 

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I replaced the NGK's with Denso Iridiums as well, along with an oil change and tranny fluid replacement, and there was a definite improvement in a vibration around 4K RPM (it's gone). Not sure if it was the plugs or the tranny fluid though....
 

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Very interesting feedback guys... mixed results as expected, but in the worst case (DeaneG) it meant business-as-usual relative to the NGKs... MaserBoy account seems much more in line with Mark's and my experience, and bet CGs vibration issue has more to do with the lube change than the plugs (or maybe a combination of both...)

The state in which the plugs came out speak volumes about the engine, rather than the plugs themselves, I think...

Keep 'em coming...
 

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i even put them in my

toyota... i noticed better performance and smoother idle... it might be that you only had six thousand miles on your plugs.... plugs degrade with use.
 

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Deane you will see a consistant performance from the Densos the NGK at 6k would not have degraded enough for it to be perceptable the guys on here with 18 to 20 k that are changing will notice an improvement because the NGKs will be worn
 

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Discussion Starter #8
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.
 

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the denso plugs will last longer without degredation and are really only slated to give better performance gains in boosted engines...(usually a 1-2hp gain on turbo/supercharged cars)
 

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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.
Well, in my case I have changed plugs every 5 or 6K miles on the annual service, as a routine. Don't forget there is certainly a deal involving NGK to be OEM supplier...
 
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