spark plugs

[Kurt in NJ]

I got 2 sets of 3X plugs from people that say they get fouled and don’t run right, after 20 minutes of driving in my car they are clean, I used to try different spark plugs “ saving the 3X for show, left them in after a show and other than swapping in the free “bad” 3X to clean them it has been 40 years on the same plugs, still get over 20 mpg I
I would say it’s the car not the plugs