I believe there is an injector used in the exhaust putting fresh fuel in with the plug also. Or maybe thats just for the ones that shoot big flames...
Actually flamethrower kits use a spark plug in the tailpipe that gets wired to your coil. When you activate it it cuts the spark to one plug on each bank of the engine. The compression forces the unburned air/fuel mixture back out through the exhaust to be ignited by the spark plug in your tailpipes. Thats why you usually hear those guys rev up the engine before activating it because forces more fuel through the system as well as causes it to run on only 6 cylinders for a few seconds. At least thats how mine used to do it. Its hard on rings and you have to change your oil often becuse you get fuel in your oil pan.
They may have other kits on the market now though.
