Aaron, I paid about 100$ for 4 spark plugs + 37$ shipping. That is much! I wont build any pressure chambers or anything like that, instead I will test if and how much the torque and fuel economy I can get using those spark plugs in a small 1KW diesel generator. This will be much easier.
Aaron, who is Robert Krupas? Any links?
Karl, did you make any other tests than only a visual spark comparison?
Thanks,
Jetijs