If you're looking for short flames, like you see on some of the old hot rods, you will need to remove your cat. no need to unplug your o2 sensor. the trick is to rev your engine and activate your flame as you let off the gas. Suddenly closing your throttle will cause your engine to run rich momentarily. adding spark in your exhaust should givew you a 1-3 ft blue flame as your engine slows back down. this will probably work better on a carbureted engine, but you should be able to get some results from fuel injection with no catalytic converter.
remember you have to have some means of creating multiple repeated sparks. if you hook up a coil and spark plug it will only spark once for each time the coil is energized.
if you aren't planning on removing your cat, or you want 10+ft flames you will need some kind of propane system. and I don't have any good advice for that.
good luck and be careful.
! .
