Different tasks and problems have to be solved during the design of screw machines; they cover the search for the most effective and reliable design solutions, connected with organizing the working process, the choice of flow path design variations, strength calculation of mechanical parts and choice of constructional materials. We have considered increasing the effectiveness of the suction process by means of sucked in gas kinetic head. To achieve this, the time span, during which the suction window connects the suction chamber with the twin cavity when the twin screw tooth has completely left it, has to be equal to shock wave duration running from discharge face to suction face. The influence of the rotor length to rotor diameter ratio and of the opening angle of the suction window on the integrated characteristics of the compressor are studied. The calculation of the working process in the compressor was performed by means of mathematical modeling. The obtained results show that the coefficient of capacity variation could reach 5 %. Increasing the opening angle of the suction window causes leakages to grow between the compression cavity and the suction chamber, which could reach 20 %.