Skyhawk 172/Cutlass 172
Flight Crew Instrument; Flight Crew Private
Flight Crew Last 90 Days 20; Flight Crew Total 270; Flight Crew Type 100
Situational Awareness
Aircraft Equipment Problem Critical
Flight Crew Diverted; Flight Crew Landed As Precaution
Human Factors; Aircraft
I was flying VFR in VMC conditions with a safety pilot in the right seat. I was flying at 3;000ft under an overlying Class Bravo airspace shelf at 5;000ft. In my mind I had intended to stay at 3;000ft for the relatively short flight but had never verbalized it to the safety pilot. The safety pilot prompted me to start a climb to a higher altitude. I went ahead and initiated the unplanned climb in a now overlying 6;000ft Class Bravo shelf and started a turn to the South/Southwest at the safety pilot's suggestion as well. Shortly thereafter; I identified a lower Class Bravo shelf of 3;600 ft between us and our direction of flight. I initiated an immediate descent and began a 180 degree turn to remain within the overlying 6;000ft Class Bravo shelf. As soon as I initiated the descent I heard a very loud bang come from the engine. I had never heard anything like the loud bang before. I identified an uncontrolled airport to the west of my position and what I thought was within potential gliding distance. I stopped my initial turn and continued my descent heading towards the uncontrolled airport. As I descended; the engine made continuous banging noises; but the noises were quieter than the initial loud bang. I was concerned the engine was going to quit functioning and continued my descent to the uncontrolled airport where I made a precautionary landing. The uncontrolled airport was underneath the 3;600ft Class Bravo shelf. In the future it will be important to assure I discuss plans; routes; altitudes; etc. with the safety pilot before the flight as well as requesting VFR flight following near Bravo airspace.
[Report narrative contained no additional information.]
C172 pilot and safety pilot reported diverting to a nearby alternate airport when the engine began to backfire.