I did that once. Used the spark plug in the tailpipe and hooked up an extra windshield washer pump/tank to dump fuel into the exhaust system just behind the mufflers 'Twas on a '68 Impalla with a punched out 350..'Twas also a big mistake, I think about it and begin to shake all over again!
At a stage in my life where we had WAY too much time on our hands.
When that hot fuel hit that spark plug and then escaped from the tailpipe, well to say the least it was both fearful and wonderous!
It was pretty.... for a second. you really need to meter the fuel down! Thank god we were not within 50 feet of a building, I almost wish that everyone had cell phone cameras back then like we do now, but then again if might be better that there is no evidence.
The fireball engulfed the back of the car and sort of held together and rose into the sky! Probably only 30 to 50 feet but it seemed like hundreds!
In the end there was no damaged done. I guess god takes care of idiots sometimes.
Definitely falls under the "kids do not try this at home" catagory.
Then there was the time we put a 50/50 Oxygen and Acetyline into one of those big punch balls (balloon on an elastic tether) and set it off, but I am still dening that episode so I cannot talk about it here......