In the 50's we used to melt the tops off pistons with HOT plugs. I would stick to the manf. recom. with these engines. You might drive the O2 sensor nuts. Hot plugs cause nitrates and nitrides to skyrocket. Not to mention the spark sensor.
The great thing about the I6 is its easy to change the plugs! He** I can do it. So if you like to change plugs and needlessly spend money give it a try maybe you would have better luck getting them to perform. Lol
I would stay with the OEM iridium delcos, they are good plugs and seem to be the best for the I6. Pricey though! check the gap before you put them in. "factory gapped my a**" mine were all jacked up
I know that you're looking for performance increases, and I'm definitely not against playing around to see what happens, but in the case of the 4.2 I-6 engine, Chevy did their homework pretty well. I doubt that there is much in the way of improvement via something like spark plugs.
If a simple heat range change would or could have made a drastic difference, I suspect that Chevy would have jumped on it. the main things plugs need to do is to burn up every atom of fuel introduced into the combustion chamber -- and from the power numbers these engines produce, I'd say they are doing that very well.
Let's face it, they are already pumping out 275/275 hp/torque from an engine that is only 242 cubic inches! That is pretty hot, right out of the box. With computer mods, a tad better breathing (even exhaust is good), synthetic oil, and a fan delete, we can see in the 300 hp range (at the crank) on these engines.
Is there more? Perhaps, but not easily found, and probably not via spark plugs. BTW, I agree with running the factory-style irridium plugs. That Chevy spec'd a plug that expensive means something beside lower dealer calls for service.
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