SR-20 instructor pilot reported an engine malfunction during climb with a student on a training flight. The instructor took over the flight controls and diverted to an alternate airport under partial engine power and landed safely.

Narrative

The student and I were at Location X at 3500 ft climbing to 4000 ft and noticed that at full power we only had 50% and low manifold pressure roughly 10-12 manifold pressure. I took over controls and tried to adjust to full power and max power was only 48% so I immediately decided to head towards ZZZ and try to maintain altitude as I felt like it was unsafe to try to attempt to go back to ZZZ1. I tried to trouble shoot putting fuel pump on and enriched the mixture. This did not resolve the problem so I made a call to ZZZ traffic to get priority to land at the airport. I entered the right downwind for [Runway] XX and tried to come in fast and high as full power was no roughly 35-40%. I ran through my landing checklist and was able to landings safely. When I taxied off the runway I went to the run up to attempt to do full power and still max power was only at 35-45% with low manifold pressure below the green; RPM max was 2650. I decided to park and squawk the aircraft as I felt it was unsafe and we wouldn't have made it to ZZZ1. No CAS message displayed.