Cessna 400 pilot reported diverting to a nearby airport after experiencing engine power loss.

Narrative

On Day 6; Pilot in Command; Person A; and I conducted a test flight in my Cessna 400 as standard protocol after an annual. Person A would fly while I monitored the engine gauges. The plane was returned to service on Day 0 by Company located at ZZZ. The mechanic provided me with the requirements and spec sheets established by Continental on what specs to fly at including speed; temperatures; etc. Person A and I reviewed the requirements with the mechanic several days prior to departure. He emphasized the importance of keeping the CHT below 400 as per the Continental manual.We planned our flight path to ZZZ1. We left ZZZ at XA00. We had a normal climb out in VFR conditions to 4500 ft. We asked for flight following from ZZZ Approach. All engine parameters were normal. We monitored gauges and at approximately XA15 we noticed the #4 cylinder was running hotter than all the other cylinders. We attempted to enrich the fuel to cool that cylinder. We then noticed our oil pressure was fluctuating. A few minutes later we noticed the oil pressure drop further. We discussed returning to ZZZ. Then we heard a loud bang in the engine area. We started losing power. We enriched full in prop and mixture. I pressed 'nearest airport' on my GPS. ZZZ2 was 3 miles away and we made a call to ZZZ1. We made a safe landing at XA25 and could not determine the cause of the issue at that time. On the ground; we contacted ZZZ1 and let them know we had a safe landing with no injuries.