On October 19, 1996, at 1700 central daylight time, an Aero Commander 685, N58RG, piloted by a private pilot, was destroyed during a collision with terrain, shortly after takeoff from a private airstrip (1400' X 90' dry/turf) in Eden, Wisconsin. A witness said he heard one of the engines sputter. The airplane then entered a left bank prior to impact. The private pilot reported serious injuries. The 14 CFR Part 91 flight was not operating on a flight plan. Visual meteorological conditions prevailed at the time of the accident. The flight departed a private airstrip in Eden, Wisconsin, at 1700 cdt. According to the pilot's written statement, he departed his private airstrip and indicated he lost boost or RPM on the left engine shortly after liftoff. The pilot applied right rudder but the airplane continued to the left. The left wing struck a tree approximately 20 feet high. The airplane started to roll towards the left and impacted the ground with the left wing first and cartwheeled. The pilot reported that both engines were running after impact and had to be shut down. According to the pilot's written statement to the FAA, he stated that on the day of the accident he noticed fuel flow was not reaching a minimum 290 lbs/hr on the left engine. The pilot, who is not an A&P mechanic, adjusted the fuel pump by-pass to achieve minimum requirements. On takeoff, the pilot stated that the left engine seemed like it lost boost pressure for a second and came right back. This happened twice on takeoff roll. The pilot stated, "At decision point, 1100', I [pilot] elected to take off. I [pilot] recall engine losing a little power again and was unable to totally correct for the drift to the left. Thus striking the top of the trees, resulting in forced landing in the neighbor's field." On December 3, 1996, during a telephone interview conducted by the IIC with the pilot, he said, "...I [pilot] pulled back too much on the yoke and stalled the airplane trying to get over the trees on the left side... ." "...I [pilot] should have push the yoke forward instead, to gain my airspeed back... ." The IIC calculated the takeoff roll using the Pilot's Operating Handbook (POH), to be 2,500 feet needed on a dry paved runway. The POH dos not have any performance charts for turf runway conditions. The left engine turbocharger and the related systems were tested by Allied Signal Aerospace under the supervision of a NTSB Investigator. Examination of the turbocharger revealed corrosion on the turbine side. The internal squirt hole that directs oil to the turbine end of the center housing for cooling was plugged shut with a coke and corrosion like material. The compressor end of the turbine shaft had a bead blasted finish. The controller, pressure relief valve, and poppet type wastegate were tested, and found to be acceptable. Nothing was found, that would preclude operation of the turbocharger and components prior to impact.