Has Anyone Used these Plugs?


Mr. Dull
Oct 4, 2005
Can anyone tell be about their performace gains with these plugs. I have always used AC R42TS. Kenny Duttweiler uses these Denso Iridiums gapped at 28.


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I used Denso plugs in my 2nd Gen DSM and in my Honda. They worked great and are actually prefered in high perf. hondas...or so I have been told. So I bought them, and was happy. As far as the Buicks go, I have been told to just use stock...but then again your new set-up is far from stock ;).
I agree. Ive used them in several N/A cars with great results, namely improved idle quality and smoothness of engine under wider operating conditions (lean burn, cold engine, etc.) These are OEM in most cars produced over the last few years by GM and many Japanese manufacturers.

However, I see a problem with using them in any DIS system, and ive seen unusual plug wear patterns over long periods of use to support my claim. As you know the DIS system, utilizing 3 coil packs to fire 6 cylinders, will fire 3 spark plugs "backwards" from your typical distributor equiped ignition system. Now, if youve studied electrostatics or electricity much, some basic knowledge about electrodes states that in bridging a gap, the sharper and smaller the point the less voltage will be required to create an arc. That means, that the smaller iridium(for reduced wear, not conductivity) will require less voltage to bridge the gap, thus allowing for larger gaps and a better spark projection. If you turn that situation around however, as in the case of the DIS system, it turns out that it is much much harder for a spark to jump a gap from a large wide electrode, to a nearly non-existent center electrode. It will require a tighter gap, will be more suceptible to blowing out under extreme load, or misfiring, and will result in wear characteristics not unlike traditional plugs on 3 cylinders. That is to say, only 3 of your expensive irridium plugs will last longer than a traditional style plug on a DIS car.

The idea of a small electrode is a fantastic principle for a spark plug, but it isnt the best in this design configuration for a DIS equipped vehicle. Double platinum spark plugs however, with small thin pieces of platinum serving as the ion transfering electrode surface, will result in very long life, better ignition on all cylinders, proper wear characteristics on a DIS system, and it appears the same benefits of the irridium plug.

If your using a distributor go for the irridiums, they will be nice. If your still using the DIS, forget it and run regular A/Cs gapped tight or try some double platinum plugs for fun/less strain on your ignition system.