I have been told that backfires are really tough on the exhaust valve. Back before locking steering wheels, I had a '66 Ford pickup. I used to turn the key off for a couple seconds while coasting past someone, then turn it back on. The backfires were spectacular and it was fun to watch the people jump. My dad, from whom I learned that reprehensible behavior
, once blew his muffler right off doing that.