Just thought I would share my experience and perhaps assist others going the same route.
Aircraft: RANS S6 with Jabiru 2200A engine.
I had a slight "crackle" when receiving and transmitting on my radio (ATR500), so I decided to fit resistor type spark plugs. The 2200A engine calls for NGK D9EA plugs and I decided to fit NGK DR9EA plugs. The engine ran fine until full throttle for takeoff where the engine showed a distinct lack of power. As I had a nice long runway there was no problem getting airborne but nevertheless decided to circle rouind and land.
I then changed back to the original plugs and full power was attained for takeoff.
I can only surmize that the extra resistance in the DR9EA plugs was just too much for the ignition system.
I've added this to the RANS S6 section aswell.
Richard
Hampshire
UK