I had an exhaust valve stick open in a Cessna 150 (O-200, 4 cylinder) cruise
and it resulted in a dead miss that nothing helped. I was able to maintain
altitude at full throttle and made it to a grass field about 10 miles away
(thank you ATC for the suggested heading) - seemed like a half hour, waiting
for something to crater completely.

"They" say a 6 cylinder engine will fly on 5, but it gets iffy with only 3
working in a 4 cylider engine.