Generally speaking, a straight piped exhaust has had the muffler(s), H-pipe, catalytic converter(s), and resonator(s) removed. This is considered to be the original (muscle car era) straight pipe ...

Then, as you run the vehicle, the additive cycles through the fuel system and out the exhaust pipes, traveling through the catalytic converter and, hopefully, removing any excess gunk and carbon ...

Car owners sometimes find, to their dismay, that their catalytic converters have been stolen because of the platinum inside.

Car exhaust flame throwers work by interrupting ... It would foul the O2 sensors and catalytic converter. Never the less, our fascination with electricity will live on.