fire from exaust?
 

can someone explain to me how that works?

Fuel + air + spark = fire.

Questions?

do you mean on purpose or by accident?

if on accident, most a backfire.

no. i mean like how do you do it intentionally?

i've seen them plumb a line into the exhaust from a small propane bottle and have a sparkplug behind it. then in the cab you push a button to release the propane and ignite it with the sparkplug.

when i was spraying my wet shot i shot flames :) iv seen someone put a spark plug in the tip and had it hooked up some how to a coil...anyways he was running pretty damn rich and it worked lol...

Bee-R rev limiter/Gizzmo launch controller will do it.

tl;dr unburnt gas igniting in your exhaust.

Build a high c/R motor with some major overlap and make it run rich on deccel, or throw a carb on it and make it a little rich at idle.