Turbo Commander 840 pilot reported aircraft did not accelerate normally during takeoff roll. Pilot retracted landing gear during rotation resulting in aircraft belly contacting runway before aircraft began climbing.

Narrative

Date / Location / Time: On Day 0; at ZZZ around XA:00 I was landing Turbo Commander 840 on runway XX on a VFR flight. The conditions of the airport environment were dry; low wind with low traffic.Purpose: This purpose of this flight was to transport the aircraft; post maintenance. I was PIC and the only occupant of the aircraft. Preflight Factors: The aircraft owner had consistently reported and advised of a low horsepower issue; particularly noticeable during landing. However; this issue could not be replicated during multiple test flights conducted at Service Center in ZZZ1.Upon leaving the service center; the flaps were also noted inoperative due to an asymmetric deployment condition; resolving this would require a cable replacement. Conversation regarding no flaps flight in the aircraft with the Commander Service Center indicated a ferry flight would not be required. The aircraft was released from the service center maintenance on Day 0 and subsequently flown by me to ZZZ on the flight in issue on Day 0.First Landing at ZZZ on Runway XY: The horsepower on both engines; particularly the left engine; remained unusually high during the approach; with the left engine indicating between 200 and 230 HP. This residual power made it difficult to slow the aircraft; a challenge further compounded by the inability to deploy flaps for additional drag. As a result; touchdown occurred above blue line airspeed. This landing was otherwise normal and was to a full stop and taxi back to runway XY. Second Takeoff From Runway XY: A second takeoff was conducted to verify the potential engine power issues in a controlled manner. The goal was to accurately identify and document the abnormality to communicate this to maintenance staff ahead of scheduled owner training in the coming weeks.Lower Power: During the takeoff roll; engine and airspeed seemed to advance normally. However; at rotation; it appeared the aircraft engines were not producing the expected power output and acceleration. In the moment; I needed to make a timely decision whether to abort or continue the takeoff. All factors considered and remaining runway length; I opted to continue the takeoff. In an effort to assist with potential lower power; decided to retract the gear right at that moment; earlier than normal; to reduce drag and aid climbout.Event: However; due to the low energy state and normal motion of flight; the aircraft belly briefly contacted the runway on the belly before managing a climbout. The pattern flight continued without incident; and I landed normally back on runway XY.