Experiments were carried out by using a new modified header modification made on CLAAS Dominator 68™ harvesting combine. This work done to minimize header losses for soybean harvesting and to trace the effects of combine forward speeds of 1.92, 2.25, 2.41 and 3.11km/h; reel speeds of 0.94, 1.06, 1.30m/s (17, 20 and 24rpm) and crop moisture content of 18, 15 and 12% while, area of plates of seed collection was kept constant at 4.5m² during experiments on productivity of the machine, losses rate of combine header, percentage of seed damage due to threshing process, proportion of total losses of combine, power required, cost analysis and criterion function cost. Surveys before modification at experiment limit indicated that, the rate of header losses were ranged from 4.6 to 11.9%. However, the rate of total losses were ranged from 6.3 to 16.5%. While, results after modification indicated that, the machine productivity was 1.735ton/fed. Also, the minimum header losses, rate of threshing damage and total losses were 1.6, 1.3 and 3.1%, respectively. On the other hand, the minimum values of power consumed and energy required were 67.4kW and 31.45kW.h/fed, respectively. In addition to, the minimum operating cost required was 96.8LE/fed while, the minimum criterion function cost was 375.7LE/fed.