The paper deals with the analysis of capacity, fuel specific expenses and price dependence on a combine harvester engine capacity.  The optimum capacity relevant for minimum expenses in grain crops harvesting is determined on the basis of the results obtained.

The article deals with the regression analysis of dependence of bandwidth, specific fuel consumption and the price on combine harvesters motor power. We applied the results of testing combine harvesters produced in the CIS and the EU and the U.S., as well as scientific works of domestic and foreign scholars in the field of technical support of agriculture. Options of curvilinear regressions were determined by the method of least squares, by their transforming into linear equations (by logarithming regression equation and the corresponding change of the variables).

Nominal performance of a combine has been considered proportional to the bandwidth. The proportionality factor (Pf) depends on the humidity, the ratio of the grain and straw yields mass, crop debris. For standard conditions, harvesting grain in Ukraine and CIS countries (humidity 14-16 %, mass ratio of grain and straw 1:1.5, straw volume factor of 0.6, weight of 1000 seeds equal 40 g , yield 40 t/ha crop infestation no more than 5% grain loss 1.1%) Pf = 1.44.

Considering the price for diesel fuel (7200 UAH / t) , machine operators payment (20 € / h), the nominal annual work hours (170 hours) and the NBU exchange rate ( 7.99 ), we have found out with curvilinear regression for  generalized combine harvester made in  CIS, the cost of gathering one ton of grain yield with minimal power output ~ 175 kW. This means that the power harvesting for "Don - 1500", "Slavutych", "Skiff " are close to the optimum value. For the capacities of  more than 175 kW costs of gathering 1t of grain gradually increases, thus the gain by increasing the bandwidth overlaps increases costs for fuel and lubricants, current and capital repairs and depreciation costs of reproduction techniques. To combine the generalized production of the EU and the U.S. minimal costs for harvesting grain correspond to engine power ~ 140 kW.

From the comparative analysis we found out that the cost of gathering one ton of grain at a nominal seasonal load is 1.7 times lower for combine harvesters produced in the CIS. With the increased seasonal loading for one combine harvester the costs are reduced significantly for both combine harvesters produced in the CIS and the EU and the U.S. , and in more recent ones. It is concluded that the use of these combine harvesting machines in the EU and the U.S. is cost-effective only if their maximum load during process in the entire period of harvesting in large size grain acreage farms and machine-tractor stations.

Key words: machine park, combine harvester optimum engine capacity, costs of one ton of grain cleaning.