The helicopter pilot reported that he was being evaluated for a pilot position with a perspective employer, who was a pilot-rated passenger who occupied the right front seat. The pilot in the left seat was asked to perform an autorotation as part of the evaluation, and he complied. During the autorotation entry phase, the pilot noticed that the rotor and engine needles split, and the engine tachometer indicated 0 RPM, and the pilot believed that the engine had failed. The airplane pilot-rated passenger in the right seat, remarked that it was a, "helluva (needle) split." The pilot maintained the rotor RPM in the green and entered the flare about 40ft above the ground. He attempted to cushion the landing, but the helicopter landed hard. When asked during an interview with FAA Aviation Safety Inspectors, the pilot reported that he could not hear if the engine was running because he was wearing a noise canceling headset. The FAA Inspector that performed the post-accident helicopter examination reported that the throttle linkage functioned normally. All spark plugs were removed and examined with indications of normal combustion. A fuel sample was obtained through the sump valve and revealed no indication of water or particulate contamination. According to the FAA Inspector, the wreckage examination failed to identify any discrepancy or malfunction of the airframe, or its components, that would have contributed to the mishap." The helicopter sustained substantial damage to the horizontal airframe tube cross-member.