The article shows that in comparison with hydraulic and electric auxiliary braking systems, the engine brake has a simpler design, several times lower weight and cost. It can be installed in the exhaust pipe of almost any car, and its application gives a significant socio-economic effect. A mathematical model has been developed for the theoretical study of the power of motor brakes with a constant choke and with an electro-magnetic valve. A theoretical study of the ZMZ-406 engine with a motor brake with a constant choke and an electromagnetic valve has been carried out. The analysis of the research results showed that a motor brake with an electromagnetic valve provides a greater braking power of the internal combustion engine, and, consequently, a better vehicle braking efficiency. Keywords: research, car, engine brake, throttle, solenoid valve, power