The first article describes the methodology and results of an experimental study of the effect of temperature and humidity on intake on the effective performance of diesel fuel YMZ-236. As a result of the work carried out, the recommendedcoefficients for adjusting the power of the YAMZ-236 diesel engine according to the temperature and humidity of the air at the intake . The second article describes the method of choosing the modes of operation of the hydrotransformer, based on the technical and economic analysis of the impact of these modes on the cost of transport operation of the car. As a result of the work done, recommendations were given for the selection of optimal modes of operation of the hydrotransformatoran bus of urban type . The third article discusses the fundamentals of achieving high strength during induction quenching. Described a new method of hardeningthe method of contour-induction hardening of the gears of steel of reduced stonyness with through heating of the tooth crown. The results of the study of mechanical properties of steels and the fine crystal structure of martensite after quenching are presented . in. h. The different modes....................................... It is established that the new method of contour induction quenching provides optimal properties of the quenched layer with the correct choice of heating temperature of the quenching . Recommendations are given for choosing the optimal mode of tightening t. in. h.