U really dont need any kind of spark plugs. What you basically need to do is get rid of your catalitic converter. The purpose of the catalytic converter is to burn up all unburned fuel that comes out of the engine. Thus if you have fuel burning in the exhaust. If you have lots of excess fuel such as at shift poits or hi rpm where cars tend to be tuned a little richer to prevent knock the excess fuel coming off the engine will continue out the tailpipe thus you get flames.
I know I get it cuz im runnin a full 3" exhaust
its kinda cool especially when blowin someone away and all they see is a ball of fire and you pullin away.