I've done this during my mis-spent youth. In the pre-cat days, we'd pull one plug wire off the engine, and extend it to near the end of the tailpipe. The unburnt charge from the the unplugged cylinder would catch fire at the rear of the tailpipe plug and blow out a good 3' flame, pulsating, freq dependent on engine speed.

I'd tune the added oxygen amount with a sleeve on the exh pipe with slots = to the tailpipe slots, and turn the sleeve to adjust the pipe opening and thus the air pulled in. You gotta hit close to stoichiometric mix to get ignition.

Not responsible for advice not taken...