On Tue, 17 Mar 2015 10:43:01 -0400, wrote:


You have 2 kinds of things that might be called backfire. It can pop
back through the carburetor and that might actually indicate a bad
intake valve or you can have a muffler explosion and that is usually a
cessation or failure of ignition (how your buddy made it happen,
flipping the key off and on)
Raw gas builds up in the exhaust and the next time a valve opens on a
burning cylinder, kaboom.
It can split a muffler open.


I did that once when I was young. It just blew the muffler wide open.
Needless to say, that was the LAST time I did it!

A fairly common practice among "gear heads" back in the 50's and 60's
was to connect a spark plug right near the tip of the tailpipe. Somehow
they would use a part often called a "vibrator", which was used in old
vacuum tube car radios to convert DC to AC. That was fed to a capacitor
and a spare ignition coil, which then provided a spark in the spark plug
at the tail pipe outlet. The cars back then, had no catalytic
converters and allowed raw heated gas to exit the exhaust system. That
spark plug ignited those raw gasses and would blow a fairly large flame
out of the tailpipe. It looked "COOL". It was pretty harmless, unless
someone got too close and set their pants or dress on fire!

I suppose you might still be able to make it happen but it is probably
tougher on an EFI with all of the emission controls.